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From the Laboratory of Cell Biology, NHLBI, National Institutes of
Health, Bethesda, Maryland 20892
INTRODUCTION Myosins have been traditionally viewed as
mechanochemical, actin-activated MgATPases that convert the energy of
ATP hydrolysis into force between actin and myosin filaments exhibited
as either movement (isotonic contraction) or tension (isometric
contraction). ``Conventional'' myosins, i.e. myosins that
form filaments, consist of a pair of heavy chains (~200 kDa) and two
pairs of light chains, the regulatory light chain and the essential
light chain. Each heavy chain has an N-terminal, globular head, where
the actin-activated ATPase activity resides, and a C-terminal tail,
through which the two heavy chains interact to form an Ca2+ activates muscle actomyosins predominantly in one of
two general ways (1, 2): (i) actin-based regulation in which
Ca2+ binds to troponin C, a component of the
tropomyosin-troponin complex that lies in the groove of the For many years, myosin filaments, as well as actin filaments, were
thought to be essential for physiologically meaningful interactions of
actin and myosin. The discovery of monomeric Acanthamoeba
myosin I (3), however, proved that single-headed, nonfilamentous
myosins, i.e. ``unconventional'' myosins, could exert
force between, and translocate along, actin filaments. This expanded
the potential physiological roles for myosins beyond those that might
be performed by filamentous myosins and initiated a search for other
unconventional myosins. We now recognize the existence of a myosin
family presently comprising 11 classes defined by the extent of
sequence homology within the subfragment-1
(S-1)1 domain: 10 unconventional myosin
classes and 1 conventional (so named because it was the first to be
discovered) class. There are several excellent recent reviews of the
sequence, structural diversity, and possible biological functions of
the multiple members of this extended family (1, 4, 5, 6).
Most conventional (class II, by the current classification system)
nonmuscle myosins are regulated by phosphorylation of their regulatory
light chains, similarly to smooth muscle myosin (7). All unconventional
myosins contain at least one light chain which, with the notable
exception of the amoeba myosins, appears to be calmodulin (4, 8). In
some cases, calmodulin has been shown to be associated with the
purified myosin, but in many cases a calmodulin light chain is inferred
from the heavy chain sequence, which can contain from one to six
calmodulin-binding IQ motifs in the light chain-binding region (4, 8).
The IQ motifs and the regulation of unconventional myosins by
Ca2+ interacting with calmodulin, which is reminiscent even
if different in detail (e.g. in some cases Ca2+
causes calmodulin to dissociate from the heavy chain with loss of
actomyosin activities) of the regulation of molluscan myosins, were
reviewed recently (4, 8, 9) and will not be discussed here.
Early in the study of the Acanthamoeba myosins it became
clear that they were regulated exclusively by a heretofore unknown
mechanism: heavy chain phosphorylation (10). The phosphorylation occurs
in the S-1 domain of the unconventional, class I myosins, as one might
expect for a covalent modification that regulates MgATPase activity,
but, and quite unexpectedly, near or at the end of the C-terminal tail
of the conventional, class II myosin (6). The latter modification is
quite remote from the regulated ATPase site in the S-1 domain and
separated from it by a relatively rigid Thus far, only Acanthamoeba, Dictyostelium, and
Physarum myosins have been shown definitively to be
regulated by heavy chain phosphorylation. However, there are numerous
examples of heavy chain phosphorylation of vertebrate nonmuscle class
II myosins, in vivo as well as in vitro, with as
yet no known substantial biochemical or physiological consequences (6,
11). Heavy chain phosphorylation of vertebrate nonmuscle class II
myosins deserves more attention than it has received. Possibly this
review will stimulate interest in those systems.
In addition to novel mechanisms for regulation of actomyosin MgATPase
activity, an emerging feature from the study of unconventional myosins
is the probable role of their nonfilamentous tails in regulating
function. Tail domains may determine the intracellular localization of
the myosin and the physiological task for which the mechanochemical
activity of its S-1 domain is used. This aspect of unconventional
myosins will be briefly addressed.
Regulation of Class II Amoeba Myosins by Heavy Chain
Phosphorylation Three conventional amoeba myosins have been studied, two in
considerable detail. Acanthamoeba myosin II is regulated
only by heavy chain phosphorylation while Dictyostelium and
Physarum myosins II are regulated by phosphorylation of
light and heavy chains. Heavy chain phosphorylation inhibits the
activities of Acanthamoeba and Dictyostelium
myosins (but by different mechanisms) while heavy chain phosphorylation
activates Physarum myosin II. Because relatively little is
known about the details of regulation of Physarum class II
myosin by heavy chain phosphorylation (6), it will not be discussed
further.
The relatively short (171 kDa) heavy
chains of this conventional myosin (5) comprise a ~90-kDa S-1 domain
and an ~80-kDa
Phosphorylation of up to 3 serine residues at the tip of the nonhelical
tail almost totally inactivates actomyosin MgATPase activity in the S-1
head by reduction of Vmax with no effect on
Kapp (the actin concentration required for
half-maximal activity) (13). Heavy chain phosphorylation also inhibits
the in vitro motility activity of Acanthamoeba
myosin II (14), the ability of myosin fixed to a substrate to
translocate actin filaments. Under assay conditions in vitro
(14) (and almost certainly also in situ (15)),
Acanthamoeba myosin II is in short minifilaments (12) with
the phosphorylation sites at the tip of the tail far removed from the
S-1 domain of the same or other myosin molecules in the minifilament
(Fig. 1). However, the phosphorylation sites and the hinge regions of
most of the molecules in the filament are relatively tightly clustered
(Fig. 1). It was proposed, therefore, that the state of phosphorylation
of the tails regulates the actomyosin MgATPase activity of the heads of
all of the molecules in the filament by altering the conformation of
the hinge regions (16), i.e. the filament is regulated
cooperatively and not the myosin molecules individually. Experimental
observations consistent with this proposal include (16, 17, 18): (i)
phosphorylation does not affect the actomyosin MgATPase activity of
monomers (which can be monitored under special circumstances); (ii)
phosphorylated myosin inactivates unphosphorylated myosin in
copolymers; and (iii) phosphorylated LMM inactivates unphosphorylated
native myosin in copolymers (and, reciprocally, unphosphorylated LMM
activates phosphorylated native myosin).
Electric birefringence studies provide direct evidence that tail
phosphorylation affects the conformation of the hinge region (19). The
hinge regions of active, unphosphorylated minifilaments are much more
rigid than the hinge regions of inactive, phosphorylated minifilaments
with the maximal difference occurring at the optimum Mg2+
concentration for actomyosin MgATPase activity. Moreover, the
Mg2+ dependency curves of enzymatic activity and rod
flexibility are essentially identical (19). And, recently, binding
of nucleotide to the globular heads was shown to increase
substantially the flexibility of unphosphorylated minifilaments (20).
This leads to the suggestions that cyclical changes in the flexibility
of the HMM/LMM hinge are tightly coupled to the S-1 ATPase-cross-bridge
cycle of the F-actin-myosin II minifilament complex and that
actin-activated MgATPase of phosphorylated myosin II is inhibited
because the hinge is trapped in its maximally flexible state. The
possibility of analogous relationships between the rod and head of
other class II myosins, including muscle myosins, should be
considered.
While the effect of phosphorylation of the C-terminal tail on the
flexibility of the HMM/LMM hinge may be explained by the proximity of
tails and hinges in the minifilament, it is more difficult to
rationalize the profound effect of nucleotide bound to the S-1 domain
on the flexibility of the hinge region. It is as if
Mg-nucleotide-induced conformational changes in the head were
transmitted to the hinge region through the This conventional myosin is regulated
by phosphorylation of both its 18-kDa regulatory light chain and its
243-kDa heavy chain. The reader is referred to a recent review (24) of
some particularly interesting studies of the regulatory role of the
light chain that are beyond the scope of this article.
Two of the possibly four or more Dictyostelium myosin II
heavy chain kinases (6, 7) have been studied in some detail. MHCK-A, a
soluble kinase present in vegetative cells, is a multimer of a 130-kDa
subunit with no sequence similarity to any other known eukaryotic
kinase (25); its N-terminal ~500 residues are predicted to be in an
In direct contrast to the effect of heavy chain phosphorylation on
Acanthamoeba myosin II, heavy chain phosphorylation of
Dictyostelium myosin II has little or no effect on the
Vmax of its actomyosin MgATPase (25) but
markedly inhibits filament formation by stabilizing a
polymerization-incompetent bent dimer (30); this is reminiscent of the
effect of light chain phosphorylation on vertebrate myosin II (1, 2).
The biological relevance of this regulatory mechanism is evidenced by
elegant experiments (31) in which myosin II with the phosphorylatable
Thr residues replaced by either Ala or Asp residues was expressed in
myosin II null mutants. The Ala mutant (which polymerized in
vitro like unphosphorylated wild type myosin II) overassembled
in vivo and supported relatively normal cell morphology and
cell motility; the Asp mutant (which behaved in vitro like
phosphorylated wild type myosin II) underassembled in vivo
and did not support normal function or morphology of myosin II null
cells. Very similar results were obtained by disrupting or
overexpressing the MHCK-A gene (32). In analogous experiments (33),
elimination of the expression of MHC-PKC abolished phosphorylation of
the myosin II heavy chain in cAMP-stimulated cells resulting in
overassembly of myosin II filaments and abnormal cell morphology and
cell motility. Conversely, overexpression of MHC-PKC resulted in
abnormally high levels of heavy chain phosphorylation, impaired myosin
II localization, and blocked cell polarization and chemotaxis.
Regulation of Class I Amoeba Myosins by Heavy Chain
Phosphorylation Acanthamoeba myosin I (by current nomenclature (8), a
class I subclass-1 myosin) was the first unconventional myosin to be
discovered (3, 10). The three known Acanthamoeba myosin I
isozymes share the features illustrated in Fig. 2: a
single heavy chain with an ~80-kDa S-1 head and a short, non-helical
~50-kDa tail (10, 34). The tail of this monomeric myosin can be
divided into three regions (34): (i) a very basic, phospholipid- and
membrane-binding region near the head/tail junction (35); (ii) a
Gly/Ala/Pro-rich region that contains an ATP-insensitive, actin-binding
site (36); and (iii) a ~50-residue segment highly homologous to Src
homology region 3 (34). These myosins have one or two light chains
(different for each isozyme) of unknown function (10). Two of the five
Dictyostelium class I myosins have similar structures while
the other three are shorter, lacking the actin-binding region in the
tail (4, 8, 34). Long and short forms of myosin I also occur in many
other species including vertebrates (4, 8).
The very high actomyosin MgATPase activity of the three
Acanthamoeba myosin I isozymes (10) and their in
vitro motility activity (37, 38) require phosphorylation of a
single Ser or Thr residue (depending on the isozyme) in the heavy chain
(39). Actomyosin MgATPase activity is enhanced 30-50-fold,
entirely by an increase in Vmax. S-1 fragments
of Acanthamoeba myosin I also exhibit
phosphorylation-dependent actomyosin MgATPase
activity, which demonstrates that the tail domain is not required for
regulation of activity (40).
The phosphorylated residue of Acanthamoeba myosin I
corresponds to Glu-411 of chicken skeletal muscle myosin, which is
positioned at the tip of an actin-binding surface loop (residues
403-416 in chicken myosin (22)). Phosphorylation of
Acanthamoeba myosin I alters the conformation of this loop
when the myosin is associated with F-actin (41) so as to greatly
increase the rate of Pi release from the ATP site (42).
Actomyosin MgATPase activity probably requires a negative charge at
this site in the surface loop. A comparison of 80 myosins (43) revealed
that 66 (including 11 vertebrate class I myosins) have either an Asp or
Glu at this position while 9, in addition to the 3 Acanthamoeba class I myosins, have a Ser or Thr (5 Dictyostelium class I myosins, Aspergillus myosin
I (MyoA), yeast myosin I (MYO3), and class VI myosins from pig and
Drosophila (p95)) and, therefore, are presumptive substrates
for heavy chain phosphorylation (Fig. 3).
There is good evidence that phosphorylation of the heavy chain of the
Acanthamoeba myosin I isozymes is essential for their
activities in vivo as well as those assayed in
vitro. Studies with isozyme and phosphorylation
state-specific antibodies (44) demonstrate that (i) a substantial
fraction of the myosin I is phosphorylated in vivo (20-80%
depending on the isozyme), (ii) the phosphorylated forms are
preferentially enriched at motile regions of the cell such as
pseudopods and phagocytic cups, and (iii) phosphorylation of the myosin
IC associated with the contractile vacuole membrane correlates
temporally with vacuole contraction (and the presence of F-actin).
Acanthamoeba myosin I heavy
chain kinase (MIHCK) is a 97-kDa monomer that is 50-fold activated by
intermolecular autophosphorylation of 8 sites (45, 46). Association of
Acanthamoeba MIHCK with acidic phospholipids (or, to a
lesser extent, isolated plasma membranes) enhances the rates of
phosphorylation of myosin I and of kinase autophosphorylation
~20-fold (45, 47). The exact localizations of the phosphorylation
sites and whether all must be phosphorylated for maximal activation are
not known, but at least one is within the catalytic domain (48).
Ca2+/calmodulin competitively inhibits the binding of, and
activation by, acidic phospholipids (the N-terminal ~7-kDa region of
Acanthamoeba MIHCK is required for strong binding of both
phospholipid and Ca2+/calmodulin (49)). MIHCK binds to
plasma membranes in vitro and is partitioned between the
plasma membrane and the cytoplasm in vivo (50). The affinity
of MIHCK for acidic phospholipids2 and
membranes (50) is drastically inhibited by autophosphorylation
suggesting that autophosphorylation may regulate the membrane/cytoplasm
distribution of MIHCK as well as its catalytic activity.
The minimum consensus substrate sequence for Acanthamoeba
MIHCK, as determined by studies with synthetic peptides and in
agreement with the sequences around the phosphorylated residues in the
native substrates (51), is:
(K,R)X1-3(S,T)XY, where X
is a variable residue (Fig. 3). Although the position(s) of the
basic residues can vary, the position of the Tyr is critical, at least
for synthetic substrates. On the basis of this sequence specificity,
four of the Dictyostelium myosin I isozymes,
Aspergillus MyoA, and yeast MYO3 would be substrates for an
Acanthamoeba-like MIHCK, but the two class VI myosins and
one of the Dictyostelium myosin I isozymes would not, unless
tertiary folding of the native myosins compensates for the strict
sequence requirements of the synthetic peptide substrates. For example,
smooth muscle myosin regulatory light chain, which does not have Tyr at
the required position, is a good substrate for Acanthamoeba
MIHCK. As predicted, Acanthamoeba MIHCK does phosphorylate
Dictyostelium myosin I (52) and also phosphorylates a
synthetic peptide with the Aspergillus
sequence.2
Recently, a very similar MIHCK has been purified from
Dictyostelium (53). It phosphorylates and activates the
actomyosin MgATPase activity of Dictyostelium myosin ID (53)
and also phosphorylates synthetic peptides with sequences corresponding
to the phosphorylation sites of Dictyostelium and
Acanthamoeba class I myosins (54). The
Dictyostelium MIHCK is very similar to
Acanthamoeba MIHCK. It has a similar mass (110 kDa), is
activated 50-fold by autophosphorylation of up to 10 sites, and binds
to acidic phospholipids, which accelerates its autophosphorylation, and
enhancement of its autophosphorylation by phospholipids is inhibited by
Ca2+/calmodulin (54). The only significant biochemical
difference between the two kinases is that the Acanthamoeba
kinase can autophosphorylate maximally (although more slowly) in the
absence of phospholipid whereas the Dictyostelium kinase
incorporates only 1 phosphate in the absence of phospholipid.
Recent sequence data confirm the relationship between
Acanthamoeba and Dictyostelium MIHCK and show
that both are members of the PAK family. PAKs are activated by the
small GTP-binding proteins Rac and Cdc42 (55) and subsequently
autophosphorylate at multiple sites (56). The deduced amino acid
sequence of the 35-kDa catalytic domain of Acanthamoeba
MIHCK is 50% identical and 70% similar to the sequences of the
catalytic domains of vertebrate PAK and yeast STE20 and only about 25%
identical to protein kinase A, PKC, and
calmodulin-dependent kinases.3
Provocatively, the homologous sequence includes the consensus
phosphorylation sequence for Acanthamoeba
MIHCK.3 Equally exciting, the complete deduced amino acid
sequence of Dictyostelium MIHCK reveals a putative
Cdc42-binding site.4 More extensive
biochemical studies are required to establish if the amoeba kinases and
PAK are similarly regulated and have similar functions. Interestingly,
the small GTPases that activate PAK also induce plasma membrane
ruffling and reorganization of the cytoskeleton of mammalian cells in
culture (55). However, the effects of small GTPases on cell
morphology have not been shown to be the result of activation of PAK,
and the physiological substrates of PAK and STE20 are not known.
Speculatively, a myosin VI might be a substrate for vertebrate PAK, and
yeast MYO3 might be a substrate for STE20 as each has a potential
phosphorylation site (Fig. 3).
Regulation of Unconventional Myosins by Their Tails In contrast to muscle myosins, the intracellular localization of
most nonmuscle myosins is spatially and temporally regulated, and in
contrast to filamentous class II myosins, monomeric myosins must be
anchored to actin filaments or membranes to produce movement. The
myosin tails are likely to be responsible for most of these dynamic
interactions, and the conserved sequences within the tails,
e.g. the GAP (GTPase-activating protein) domain of a class
IX myosin (Myr5), the PH (pleckstrin homology) domain of a class X
myosin, and the SH3 domain of class I myosins (4, 8), are good
candidate sites for binding to structural and/or regulatory proteins.
Indeed, the exciting finding that the GAP domain of Myr5 stimulates GTP
hydrolysis by small GTP-binding proteins (57) suggests possible new
functions for myosins (it is not known how the properties of Myr5 are
affected by binding to small G-proteins), and the SH3 domain of long
class I Myr3 may regulate ATP-sensitive actin binding (58).
The membrane-binding site in the tail of both long and short
class I myosin allows them to associate with acidic phospholipids,
membranes, and vesicles in vitro and translocate them along
actin filaments (10). We do not know why the three
Acanthamoeba class I myosins localize to unique membrane
sites in vivo (44), but the recent discovery of a protein
that may bind specifically to the SH3 domain of one of the three
Acanthamoeba myosin I isozymes is a promising lead
(59). For some vertebrate class I myosins,
Ca2+-induced loss of the calmodulin light chain stimulates
binding to lipids (60, 61).
Concluding Remarks The detailed studies of the amoeba myosins briefly summarized in
this review have shown that myosins are regulated in diverse ways by
heavy chain phosphorylation. The active site of Acanthamoeba
myosin II is regulated at a distance through
phosphorylation-dependent conformational changes in the
supramolecular structure of the myosin filament,
Dictyostelium myosin II is regulated by
phosphorylation-dependent filament polymerization and
depolymerization, and the class I amoeba myosins are regulated by the
phosphorylation state of a serine or threonine in an actin-binding loop
in the myosin head. The regulatory kinases are very different than the
well studied Ca2+/calmodulin-dependent myosin
light chain kinase, and the same myosin can be regulated by more than
one kinase: PAK-like kinases for amoeba class-I myosins and an atypical
kinase (MHCK-A) and a PKC-like kinase for Dictyostelium
myosin II. Recent observations that PKC phosphorylates the tail
of the heavy chains of brain myosin II (62) and some vertebrate class I
myosins (61, 63) and that cell cycle-dependent Cdc2 kinase
phosphorylates Xenopus myosin IIB (but not myosin IIA)
near the ATP-binding site in the head (64) provide strong reasons for
believing that heavy chain phosphorylation will have as important a
regulatory role for vertebrate myosins as it does for amoeba
myosins.
FOOTNOTES REFERENCES5
Volume 271, Number 29,
Issue of July 19, 1996
pp. 16983-16986
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
MINIREVIEW:
INTRODUCTION
Regulation of Class II Amoeba Myosins by Heavy Chain
Phosphorylation
Regulation of Class I Amoeba Myosins by Heavy Chain
Phosphorylation
Regulation of Unconventional Myosins by Their Tails
Concluding Remarks
FOOTNOTES
REFERENCES5
-helical
coiled-coil rod. One of each pair of light chains is bound to the neck
region of the globular heads (subfragment-1) near the head-tail
junction. The tail also mediates the self-association of multiple
myosin molecules into bipolar thick filaments.
-helical
coiled-coil actin thin filament (skeletal muscle); (ii) myosin light
chain-based regulation in which either
Ca2+/calmodulin-dependent myosin light chain
kinase phosphorylates a serine in the regulatory light chain (smooth
muscle) or Ca2+ binds directly to the regulatory light
chain (molluscan muscle).
-helical coiled-coil, thus
posing some very interesting questions about the mechanism of signal
transduction between the phosphorylation site and the catalytic
site.
-helical coiled-coil rod separated by a hinge
region into a relatively long heavy meromyosin (HMM) domain and a short
light meromyosin (LMM) domain ending in a 29-residue nonhelical
C-terminal tail (Fig. 1). As for other conventional
myosins, there are two pairs of light chains, but their functions are
not known.
Fig. 1.
Schematic representation of a minifilament of
Acanthamoeba myosin II. The angles and directions of
the bends in the rods at the HMM/LMM junctions and the ``packing'' of
the molecules are arbitrary, and the two-dimensional display cannot, of
course, truly represent the three-dimensional structure. However, the
overlaps of the tails in the longitudinal direction (12) and the
positions of the hinge regions (6) are to scale, and, therefore, the
longitudinal relationships between the hinge regions and the
phosphorylation sites at the end of the tails are approximately
correct. Note that the hinge region of each of the 6 interior molecules
lies near the phosphorylation sites at the tip of the nonhelical tail
of an adjacent molecule. The light chains are not shown.
-helical coiled-coil of
the HMM segment. Perhaps even more remarkable, S-1-bound MgATP
increases the protease susceptibility of the C-terminal nonhelical
tails of phosphorylated minifilaments (21), and phosphorylation at the
tip of the tail shifts a predominant protease cleavage site in the S-1
head by 17 residues (21) from Lys-621 to Arg-638. From x-ray
crystallography, the corresponding residues of chicken skeletal muscle
myosin are in the second actin-binding surface loop (22). As measured
by analytical ultracentrifugation (21) and electric birefringence (20),
neither phosphorylation nor nucleotide binding affect the overall
structure of myosin II monomers or minifilaments, nor does
phosphorylation affect the critical concentration for polymerization
(23). Thus, we are left with an intriguing question. How are the
conformational changes caused by nucleotide binding to the S-1 domain
and the conformational changes caused by phosphorylation at the tip of
the tail transmitted to the opposite ends of the
Acanthamoeba myosin II molecule that are separated by an
~90-nm-long -helical coiled-coil?
-helical coiled coil, and its C-terminal ~300 residues are similar
in sequence to the 
-subunit of heterotrimeric G-proteins (26). This
kinase is activated 50-fold (Vmax) by
autophosphorylation of 3 of its 10 autophosphorylation sites (25).
MHC-PKC, a membrane-associated kinase that appears in developing cells
(27), is a multimer of an ~84-kDa subunit that contains all of the
protein kinase C-specific sequence domains (28) and 20 sites that are
autophosphorylated intramolecularly (27). MHCK-A phosphorylates three
identified Thr residues (29) in the C-terminal 25% of the -helical
coiled-coil rod (which is about twice the length of the rod of
Acanthamoeba myosin II), and MHC-PKC phosphorylates four as
yet unidentified Thr residues in the same region (27). Neither kinase
is regulated in vitro by either Ca2+/calmodulin
or cyclic nucleotides (25, 27). Although it seems logical that MHC-PKC
would be stimulated by effectors of PKC, such as diacylglycerol, these
seem not to have been tested.
Fig. 2.
Schematic representative of the structure of
an Acanthamoeba class I myosin. The locations of the
phosphorylation site (P) (39), the strongly basic,
membrane-binding site (35), the glycine/proline/alanine-rich
(G/P/A/-rich) actin-binding site (36), and the Src homology
region 3 (SH3) (34) are shown. Adapted from Ref. 34 with
permission.
Fig. 3.
Twelve myosins with a known or putative
phosphorylation site with similar sequence and at a similar position as
the phosphorylation sites of the class I myosins of Acanthamoeba
castellanii. At least 66 other myosins have either D or E at
the S/T position, and only 2 myosins are known to have neither S, T, D,
nor E at that position (43). The D in chicken skeletal muscle myosin is
at position 411 as numbered in Ref. 1. In every case, the consensus
sequence, DALAK, occurs 16 residues after the S, T, D, or E (1, 43).
The residue preceding A in Acanthamoeba myosin IA is not
known but must be either K or R as this is a trypsin-cleavage site
(41). Note that the amino acid 2 residues C-terminal to the
phosphorylation site is usually Y and occasionally I and that basic
residues are always near the phosphorylation site on the N-terminal
side. Adapted from Ref. 43 with permission.
To whom correspondence should be addressed: Bldg. 3, Rm. B1-22,
National Institutes of Health, Bethesda, MD 20892. Tel.: 301-496-2116 or 302-496-1616; Fax: 301-402-1519; E-mail: edk{at}nih.gov.
1
The abbreviations used are: S-1, subfragment-1;
HMM, heavy meromyosin; LMM, light meromyosin; MHC, myosin heavy chain;
PKC, protein kinase C; MIHCK, myosin I heavy chain kinase; MHCK, myosin
heavy chain kinase; PAK, p21-activated kinase.
2
H. Brzeska and E. D. Korn, unpublished
observation.
3
H. Brzeska, J. Szczepanowska, J. Hoey, and E. D. Korn, manuscript in preparation; presented at the 1996 annual meeting
of the Biophysical Society but not included in the published
abstract.
4
S. F. Lee, T. T. Egelhoff, A. Mahasneh, and G. P. C
té, personal communication; presented at the 1995 annual meeting of the American Society for Cell Biology but not
included in the published abstract.
5
Reviews and recent papers are sometimes cited
rather than the original paper.
té, G. P.,
Korn, E. D.
(1983)
J. Biol. Chem.
258,
6011-6014
té, G. P.
(1990)
Biochemistry
29,
8992-8997
[CrossRef][Medline]
[Order article via Infotrieve]
té, G. P.,
Egelhoff, T.
T.
(1995)
J. Biol. Chem.
270,
523-529
té, G. P.,
Albanesi, J. P.,
Ueno, T.,
Hammer, J. A., III,
Korn, E. D.
(1985)
J. Biol. Chem.
260,
4543-4546
té, G. P.
(1995)
J. Biol. Chem.
270,
11776-11782
té, G. P.
(1995)
Mol. Biol. Cell
6,
149
a
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 R. I. Ludowyke, Z. Elgundi, T. Kranenburg, J. R. Stehn, C. Schmitz-Peiffer, W. E. Hughes, and T. J. Biden Phosphorylation of Nonmuscle Myosin Heavy Chain IIA on Ser1917 Is Mediated by Protein Kinase CbetaII and Coincides with the Onset of Stimulated Degranulation of RBL-2H3 Mast Cells J. Immunol., August 1, 2006; 177(3): 1492 - 1499. [Abstract] [Full Text] [PDF]
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 U. Durrwang, S. Fujita-Becker, M. Erent, F. J. Kull, G. Tsiavaliaris, M. A. Geeves, and D. J. Manstein Dictyostelium myosin-IE is a fast molecular motor involved in phagocytosis J. Cell Sci., February 1, 2006; 119(3): 550 - 558. [Abstract] [Full Text] [PDF]
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K. Reville, J. K. Crean, S. Vivers, I. Dransfield, and C. Godson Lipoxin A4 Redistributes Myosin IIA and Cdc42 in Macrophages: Implications for Phagocytosis of Apoptotic Leukocytes J. Immunol., February 1, 2006; 176(3): 1878 - 1888. [Abstract] [Full Text] [PDF]
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 K. Kohlstedt, R. Kellner, R. Busse, and I. Fleming Signaling via the Angiotensin-Converting Enzyme Results in the Phosphorylation of the Nonmuscle Myosin Heavy Chain IIA Mol. Pharmacol., January 1, 2006; 69(1): 19 - 26. [Abstract] [Full Text] [PDF]
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X. Liu, S. Shu, M. Kovacs, and E. D. Korn Biological, Biochemical, and Kinetic Effects of Mutations of the Cardiomyopathy Loop of Dictyostelium Myosin II: IMPORTANCE OF ALA400 J. Biol. Chem., July 22, 2005; 280(29): 26974 - 26983. [Abstract] [Full Text] [PDF]
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 U. Oberholzer, T. L. Iouk, D. Y. Thomas, and M. Whiteway Functional Characterization of Myosin I Tail Regions in Candida albicans Eukaryot. Cell, October 1, 2004; 3(5): 1272 - 1286. [Abstract] [Full Text] [PDF]
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 T. Ishikawa, N. Cheng, X. Liu, E. D. Korn, and A. C. Steven Subdomain organization of the Acanthamoeba myosin IC tail from cryo-electron microscopy PNAS, August 17, 2004; 101(33): 12189 - 12194. [Abstract] [Full Text] [PDF]
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T. Gao, K. Ehrenman, L. Tang, M. Leippe, D. A. Brock, and R. H. Gomer Cells Respond to and Bind Countin, a Component of a Multisubunit Cell Number Counting Factor J. Biol. Chem., August 30, 2002; 277(36): 32596 - 32605. [Abstract] [Full Text] [PDF]
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U. Oberholzer, A. Marcil, E. Leberer, D. Y. Thomas, and M. Whiteway Myosin I Is Required for Hypha Formation in Candidaalbicans Eukaryot. Cell, April 1, 2002; 1(2): 213 - 228. [Abstract] [Full Text] [PDF]
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H. Brzeska, R. Young, C. Tan, J. Szczepanowska, and E. D. Korn Calmodulin-binding and Autoinhibitory Domains of Acanthamoeba Myosin I Heavy Chain Kinase, a p21-activated Kinase (PAK) J. Biol. Chem., December 7, 2001; 276(50): 47468 - 47473. [Abstract] [Full Text] [PDF]
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D. P. Mulvihill, C. Barretto, and J. S. Hyams Localization of Fission Yeast Type II Myosin, Myo2, to the Cytokinetic Actin Ring Is Regulated by Phosphorylation of a C-Terminal Coiled-Coil Domain and Requires a Functional Septation Initiation Network Mol. Biol. Cell, December 1, 2001; 12(12): 4044 - 4053. [Abstract] [Full Text] [PDF]
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X. Liu, N. Osherov, R. Yamashita, H. Brzeska, E. D. Korn, and G. S. May Myosin I mutants with only 1% of wild-type actin-activated MgATPase activity retain essential in vivo function(s) PNAS, July 13, 2001; (2001) 161285698. [Abstract] [Full Text] [PDF]
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B. Mayer SH3 domains: complexity in moderation J. Cell Sci., January 4, 2001; 114(7): 1253 - 1263. [Abstract] [PDF]
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 J. An, G. Zhao, L. M. Churgay, J. J. Osborne, J. E. Hale, G. W. Becker, G. Gold, L. E. Stramm, and Y. Shi Threonine phosphorylations induced by RX-871024 and insulin secretagogues in beta TC6-F7 cells Am J Physiol Endocrinol Metab, November 1, 1999; 277(5): E862 - E869. [Abstract] [Full Text] [PDF]
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D. M. Helfman, E. T. Levy, C. Berthier, M. Shtutman, D. Riveline, I. Grosheva, A. Lachish-Zalait, M. Elbaum, and A. D. Bershadsky Caldesmon Inhibits Nonmuscle Cell Contractility and Interferes with the Formation of Focal Adhesions Mol. Biol. Cell, October 1, 1999; 10(10): 3097 - 3112. [Abstract] [Full Text]
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 S. L. Rogers, R. L. Karcher, J. T. Roland, A. A. Minin, W. Steffen, and V. I. Gelfand Regulation of Melanosome Movement in the Cell Cycle by Reversible Association with Myosin V J. Cell Biol., September 20, 1999; 146(6): 1265 - 1276. [Abstract] [Full Text] [PDF]
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H. Brzeska, R. Young, U. Knaus, and E. D. Korn Myosin I heavy chain kinase: Cloning of the full-length gene and acidic lipid-dependent activation by Rac and Cdc42 PNAS, January 19, 1999; 96(2): 394 - 399. [Abstract] [Full Text] [PDF]
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Z.-Y. Wang, F. Wang, J. R. Sellers, E. D. Korn, and J. A. Hammer III Analysis of the regulatory phosphorylation site in Acanthamoeba myosin IC by using site-directed mutagenesis PNAS, December 22, 1998; 95(26): 15200 - 15205. [Abstract] [Full Text] [PDF]
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F. Buss, J. Kendrick-Jones, C. Lionne, A. E. Knight, G. P. Cote, and J. Paul Luzio The Localization of Myosin VI at the Golgi Complex and Leading Edge of Fibroblasts and Its Phosphorylation and Recruitment into Membrane Ruffles of A431 Cells after Growth Factor Stimulation J. Cell Biol., December 14, 1998; 143(6): 1535 - 1545. [Abstract] [Full Text] [PDF]
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X. Liu, K. Ito, S. Morimoto, A. Hikkoshi-Iwane, T. Yanagida, and T. Q. P. Uyeda Filament structure as an essential factor for regulation of Dictyostelium myosin by regulatory light chain phosphorylation PNAS, November 24, 1998; 95(24): 14124 - 14129. [Abstract] [Full Text] [PDF]
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S.-F. Lee, A. Mahasneh, M. de la Roche, and G. P. Cote Regulation of the p21-activated Kinase-related Dictyostelium Myosin I Heavy Chain Kinase by Autophosphorylation, Acidic Phospholipids, and Ca2+-Calmodulin J. Biol. Chem., October 23, 1998; 273(43): 27911 - 27917. [Abstract] [Full Text] [PDF]
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J. R. Wilson, R. I. Ludowyke, and T. J. Biden Nutrient Stimulation Results in a Rapid Ca2+-dependent Threonine Phosphorylation of Myosin Heavy Chain in Rat Pancreatic Islets and RINm5F Cells J. Biol. Chem., August 28, 1998; 273(35): 22729 - 22737. [Abstract] [Full Text] [PDF]
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 B.-A. Battelle, A. W. Andrews, B. G. Calman, J. R. Sellers, R. M. Greenberg, and W. C. Smith A Myosin III from Limulus Eyes Is a Clock-Regulated Phosphoprotein J. Neurosci., June 15, 1998; 18(12): 4548 - 4559. [Abstract] [Full Text] [PDF]
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L. Eichinger, M. Bahler, M. Dietz, C. Eckerskorn, and M. Schleicher Characterization and Cloning of a Dictyostelium Ste20-like Protein Kinase That Phosphorylates the Actin-binding Protein Severin J. Biol. Chem., May 22, 1998; 273(21): 12952 - 12959. [Abstract] [Full Text] [PDF]
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J. Szczepanowska, U. Ramachandran, C. J. Herring, J. M. Gruschus, J. Qin, E. D. Korn, and H. Brzeska Effect of mutating the regulatory phosphoserine and conserved threonine on the activity of the expressed catalytic domain of Acanthamoeba myosin I heavy chain kinase PNAS, April 14, 1998; 95(8): 4146 - 4151. [Abstract] [Full Text] [PDF]
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K. D. Novak and M. A. Titus The Myosin I SH3 Domain and TEDS Rule Phosphorylation Site are Required for In Vivo Function Mol. Biol. Cell, January 1, 1998; 9(1): 75 - 88. [Abstract] [Full Text]
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C. Wu, V. Lytvyn, D. Y. Thomas, and E. Leberer The Phosphorylation Site for Ste20p-like Protein Kinases Is Essential for the Function of Myosin-I in Yeast J. Biol. Chem., December 5, 1997; 272(49): 30623 - 30626. [Abstract] [Full Text] [PDF]
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H. Brzeska, U. G. Knaus, Z.-Y. Wang, G. M. Bokoch, and E. D. Korn p21-activated kinase has substrate specificity similar to Acanthamoeba myosin I heavy chain kinase and activates Acanthamoeba myosin I PNAS, February 18, 1997; 94(4): 1092 - 1095. [Abstract] [Full Text] [PDF]
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K. D. Novak and M. A. Titus Myosin I Overexpression Impairs Cell Migration J. Cell Biol., February 10, 1997; 136(3): 633 - 647. [Abstract] [Full Text] [PDF]
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C. Wu, S.-F. Lee, E. Furmaniak-Kazmierczak, G. P. Cote, D. Y. Thomas, and E. Leberer Activation of Myosin-I by Members of the Ste20p Protein Kinase Family J. Biol. Chem., December 13, 1996; 271(50): 31787 - 31790. [Abstract] [Full Text] [PDF]
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S.-F. Lee, T. T. Egelhoff, A. Mahasneh, and G. P. Cote Cloning and Characterization of a Dictyostelium Myosin I Heavy Chain Kinase Activated by Cdc42 and Rac J. Biol. Chem., October 25, 1996; 271(43): 27044 - 27048. [Abstract] [Full Text] [PDF]
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H. Brzeska, B. M. Martin, and E. D. Korn The Catalytic Domain of Acanthamoeba Myosin I Heavy Chain Kinase. I. IDENTIFICATION AND CHARACTERIZATION FOLLOWING TRYPTIC CLEAVAGE OF THE NATIVE ENZYME J. Biol. Chem., October 25, 1996; 271(43): 27049 - 27055. [Abstract] [Full Text] [PDF]
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H. Brzeska, J. Szczepanowska, J. Hoey, and E. D. Korn The Catalytic Domain of Acanthamoeba Myosin I Heavy Chain Kinase. II. EXPRESSION OF ACTIVE CATALYTIC DOMAIN AND SEQUENCE HOMOLOGY TO p21-ACTIVATED KINASE (PAK) J. Biol. Chem., October 25, 1996; 271(43): 27056 - 27062. [Abstract] [Full Text] [PDF]
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X. Liu, H. Brzeska, and E. D. Korn Functional Analysis of Tail Domains of Acanthamoeba Myosin IC by Characterization of Truncation and Deletion Mutants J. Biol. Chem., August 4, 2000; 275(32): 24886 - 24892. [Abstract] [Full Text] [PDF]
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X. Liu, N. Osherov, R. Yamashita, H. Brzeska, E. D. Korn, and G. S. May Myosin I mutants with only 1% of wild-type actin-activated MgATPase activity retain essential in vivo function(s) PNAS, July 31, 2001; 98(16): 9122 - 9127. [Abstract] [Full Text] [PDF]
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