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(Received for publication, August 14, 1995) From the
Streptococcus suis causes meningitis, sepsis, and other
serious infections in newborn and young pigs and in adult humans. The
Gal
The first event in the establishment of infectious diseases is
the adhesion of bacteria to the surface of host cells(1) .
Adhesins mediating this interaction are thus essential factors in
bacterial pathogenesis and important virulence
factors(2, 3) . Many adhesins act as lectins,
recognizing specific carbohydrate moieties on host cell surface
glycoconjugates. Most of the knowledge on bacterial
carbohydrate-binding adhesins is derived from studies on Gram-negative
bacteria (reviewed in (4) ), whereas only little information
exists on the molecular identity and detailed binding properties of
such adhesins in Gram-positive bacteria. Streptococcus suis is an important Gram-positive pathogen which causes meningitis,
sepsis, and other serious infections in piglets (5, 6, 7) and meningitis in humans who have
been in contact with pigs(8, 9) . The identification
and characterization of the molecules responsible for the interaction
of the bacteria with host cells would give valuable information for the
understanding of the pathogenesis of the infection and is a key factor
in the development of new antibacterial agents and vaccines. In
previous studies, the binding of S. suis bacteria to host
cells was found to be mediated by an adhesion activity which recognizes
the disaccharide
galactosyl-
Todd-Hewitt broth and a Gas-Pak
anaerobic system were purchased from Becton Dickinson and Co.,
Cockeysville, MD. Microwell Microtiter Plates were from Dako, Roskilde,
Denmark, and polystyrene flat bottom Microstrips from Labsystems,
Helsinki, Finland. IODOBEADS were purchased from Pierce. Bio-Gel P-6DG
Desalting Gel was from Bio-Rad. Nitrocellulose sheets were from
Schleicher & Schuell, Dassel, Germany and PVDF-P membrane from
Millipore.
Nonspecific binding sites were saturated by incubation of the
membranes for 1.5 h in phosphate buffer C (0.1 M sodium
phosphate buffer, 0.5% Tween 20, 150 mM NaCl, pH 5.3). The
membranes were incubated with the
Latex hemagglutination and hemagglutination
inhibition assays were performed as described before(14) .
Adhesin-covered latex particles (5, 10, or 25 µl) were mixed with a
4% suspension of sialidase-treated human erythrocytes (5, 10, or 25
µl, respectively) on a ceramic slide and incubated on ice for 10
min. In agglutination inhibition assays, 10 µl of adhesin-covered
latex particles were mixed with 10 µl of the inhibitory compounds
on a slide and incubated on ice. After 15 min, 20 µl of
sialidase-treated 4% human erythrocytes were added, and the mixture was
incubated for 15 min on ice. Similar agglutination reactions were
obtained in volumes of 5 to 25 µl of latex with 5 to 25 µl of
sialidase-treated erythrocytes, respectively. Bovine serum
albumin-coated latex particles (0-0.1 mg/1.25
Figure 1:
Binding of pigeon ovomucoid to S. suis bacterial cells in a dot assay. Two strains of S.
suis cells having different hemagglutinating activity (628, 1:64
and 836, 1:8) and a strain with no hemagglutinating activity (598) were
pipetted onto nitrocellulose membrane at the dilutions of 1:1, 1:10,
and 1:50 in a volume of 1 µl. After blocking nonspecific binding
sites, the membranes were incubated for 1 h with
In fractional ammonium sulfate precipitation of the
sonicate (50 mg of protein/16 ml of sonicate), the adhesin activity was
precipitated with ammonium sulfate with a saturation degree of 70% (Fig. 2). Ammonium sulfate having a saturation degree of 60%
precipitated the contaminating proteins running near the adhesin, as
analyzed by polyacrylamide gel electrophoresis in the absence of SDS
and Western blotting with radiolabeled pigeon ovomucoid.
Figure 2:
Purification of the adhesin protein by
fractional ammonium sulfate precipitation. The sonication supernatant
of S. suis strain 628 was subjected to fractional ammonium
sulfate precipitation, and the precipitates of the 60, 70, and 80%
ammonium sulfate saturation precipitates and the starting sonication
supernatant (S) were subjected to electrophoresis in 6%
polyacrylamide gels in the absence of SDS. The gel was stained for
protein (A), or the proteins were transferred to PVDF-P
membrane which was probed for adhesin activity with
The adhesin
was finally purified to homogeneity from the 70% ammonium sulfate
precipitate (1 mg of protein/16 ml of sonicate) by preparative gel
electrophoresis. Fractions from the preparative gel were collected and
analyzed by gel electrophoresis. The adhesin was eluted as a single
band (Fig. 3). Usually about 150 µg of pure adhesin was
isolated from 16 ml of a bacterial suspension of S. suis strain 628 with a hemagglutination titer of 1:32.
Figure 3:
Purification of the adhesin by preparative
gel electrophoresis. The 70% ammonium sulfate precipitate was subjected
to preparative electrophoresis in a 6% polyacrylamide gel in the
absence of SDS. Fractions of 4 ml were collected and analyzed by
analytical gel electrophoresis in a 6% gel stained for protein. The
numbers of the fractions are given. The pure adhesin was eluted in
fractions 78-83.
Figure 4:
Polyacrylamide gel electrophoresis and
isoelectric focusing of purified S. suis adhesin. A,
the purified adhesin was run in 15% polyacrylamide gel electrophoresis
in the presence of SDS which was stained with Serva Blue. The molecular
masses of the standard proteins (St1 and St2) are
indicated in kDa. B, isoelectric focusing of the adhesin by
the Phast Gel system. The gel was stained with silver. The isoelectric
points of the standard proteins (St) and the sample
application point (S) are
indicated.
The P
adhesin activity of S. suis was previously shown to occur as
two variant activities P
Figure 5:
Binding of pigeon ovomucoid to adhesin in S. suis strains with different hemagglutinating activities.
Sonicated extracts of the S. suis strains indicated (top) with differing hemagglutinating activity were separated
by electrophoresis in 6% polyacrylamide gels in the absence of SDS and
transferred to PVDF-P membrane which was probed for adhesin activity
with
The intensity of
the band correlated with the hemagglutination titers of the
corresponding strain. Like in many other bacteria(24) , the P
hemagglutination of S. suis undergoes spontaneous phase
variation. Also in bacteria extracted in the highly agglutinating or
low agglutinating phases, the intensity of the adhesin bands correlated
with the agglutinating titer (Fig. 5, strain 628).
In previous studies, we found that pigeon ovomucoid, due to
the presence of the Gal Two variant P adhesion specificities
are present in Gal Recently, a 110-kDa protein of S. suis serotype 2 has been
identified as a virulence marker(25) . Also, the capsular
polysaccharides, occurring as at least 29 serotypes, have been
suggested to play a role in the pathogenesis of infections caused by S. suis(26, 27) . The contribution of these
factors to the pathogenic mechanisms of S. suis are at present
not known. Only few adhesins have been identified and isolated from
Gram-positive bacteria. Some of these are oral strains and are related
to the binding of the bacteria to hydroxyapatite(28) ,
saliva(29) , or other bacteria (30) , or bind to
extracellular components such as fibronectin (31) or
fibrinogen(32) . These adhesins differ in molecular properties
from the P adhesin of S. suis, and their possible lectin and
cell-surface binding activities are in most cases not known or have not
been characterized in detail. In Gram-negative bacteria, adhesins from
bacteria associated with meningitis include the S-fimbrial adhesin from Escherichia coli(33, 34) and an adhesin from Neisseria meningitidis(35) . Interestingly, an N-acetylglucosamine-specific adhesin of 17 kDa has been
reported from type III group B streptococci associated with newborn
meningitis (36) but further details of the interaction and the
molecules involved are missing. The present report represents the
first isolation of Gal
Volume 270,
Number 48,
Issue of December 1, 1995 pp. 28874-28878
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
1
4-galactose-binding Adhesin from the
Gram-positive Meningitis-associated Bacterium Streptococcus suis(*)
ABSTRACT
INTRODUCTION
EXPERIMENTAL PROCEDURES
RESULTS
DISCUSSION
FOOTNOTES
ACKNOWLEDGEMENTS
REFERENCES
1-4Gal-binding adhesin of S. suis was purified
to homogeneity by ultrasonic treatment, fractional ammonium sulfate
precipitation, and preparative polyacrylamide gel electrophoresis.
Pigeon ovomucoid, a glycoprotein with Gal1-4Gal terminals,
was used to detect the adhesin by blotting. The purified adhesin
appeared as single band of an apparent size of 18 kDa and of a pI of
6.4; no disulfide bridges were present. The amount of adhesin as
revealed by pigeon ovomucoid binding correlated with the
hemagglutination activity of different S. suis strains. The
purified adhesin bound to latex particles induced hemagglutination
which was specifically inhibited with the same inhibitors as
hemagglutination by the intact bacteria, thus demonstrating that the
purified protein was the Gal1-4Gal-recognizing adhesin of S. suis. Two adhesin variants (P
and
P
) with differing Gal1-4Gal binding specificity
had the similar electrophoretic mobilities and the same N-terminal
peptide sequences, indicating that they were closely related. This
represents the first isolation of an adhesin with well-defined cell
surface carbohydrate binding activity from Gram-positive bacteria
associated with meningitis.
1-4-galactose(10, 11) . In the
present study, the adhesin was identified, purified to homogeneity, and
characterized and was found to retain the hemagglutination activity and
specificity of the intact bacteria.
Materials
Pigeon ovomucoid was purified as
described previously(12) . Hen ovomucoid, N-acetylgalactosamine, and N-acetylglucosamine were
obtained from Sigma. Galactose and mannose were obtained from Fluka,
Buchs, Switzerland. Sialidase (Vibrio cholerae) was obtained
from Behringwerke AG, Marburg, Germany. Phenylmethylsulfonyl fluoride
was obtained from Boehringer Mannheim, Germany. Bovine serum albumin
was obtained from Sigma, ammonium sulfate from Riedel-de
Haën, Seelze, Germany, and NaI from
Amersham, UK. Acrylamide, bisacrylamide, and N,N,N`,N`-tetramethylethylenediamine
(TEMED) were purchased from Bio-Rad, sodium dodecyl sulfate from Fluka.
Low molecular weight standards, isoelectric focusing standards (IEF
standard 3-10), and Phast Gel 3-9 were obtained from
Pharmacia, Sweden. Bacto-latex 0.81 standardized suspension of latex
particles was purchased from Difco.
Bacterial Strains
The S. suis strains
studied have been described before(13) . Strain 628 was
obtained from Dr H. C. Zanen, Academic Medical Centre, Amsterdam, the
Netherlands; strains TEW/2 and R75/L1 were obtained from Dr F.
Clifton-Hadley, Clinical Veterinary School, University of Cambridge,
UK, and strains 836, 825, 752, 3031, 598, 3027, and 1045 from Dr J.
Hommez, Regional Veterinary Investigation Laboratory, Torhout, Belgium.
The bacteria were maintained in Todd-Hewitt broth at -20 °C
and were grown on sheep blood agar plates overnight at 37 °C under
anaerobic conditions (Gas-Pak system). The bacteria were harvested from
the plates, washed twice, and suspended in phosphate buffer A (10
mM sodium phosphate, 0.15 M NaCl, pH 7.4) and
adjusted to a concentration that gave an A of
0.5 at 1:100 dilution.
Hemagglutination and Hemagglutination Inhibition
Assays
Erythrocytes obtained from healthy adults were washed and
treated by sialidase as described before (14) and used at 2%
concentration. The microtiter and slide hemagglutination assays were
done as described before (14) on microtiter plates using 25
µl of bacterial suspension prepared as described above.Protein Determination
Protein determination was
carried by an adaptation of the method described by Bradford (15) on polystyrene Microstrips using Bio-Rad Protein Assay Dye
Reagent Concentrate. The absorbance at A was
measured by SLT Labinstruments Easy Reader SF plus ELISA reader.
Radiolabeling of Pigeon Ovomucoid
Pigeon ovomucoid
was labeled with I using the IODOBEAD method according to
the instructions of the manufacturer. A total amount of 0.3 mCi of
Na
I was added to 250 µg of ovomucoid in 250 µl of
buffer A, and a bead was added. The reaction mixture was incubated for
30 min at room temperature with occasional shaking. The reaction
mixture was removed from the bead, and 0.5 M NaI was added to
a concentration of 10 mM. Nonincorporated iodine was separated
by chromatography on a desalting column (Bio Gel P-6DG, 1
3 cm)
equilibrated with distilled water. Bovine serum albumin was added to
the labeled pigeon ovomucoid to a concentration of 1 mg/ml, and the
preparation was stored at -80 °C and used within 2 weeks.Dot Assay and Blot Binding of Radiolabeled Pigeon
Ovomucoid
Adhesin activity was identified from whole bacterial
cells and electrophoretically separated proteins by dot and blot
binding, respectively, of radiolabeled pigeon ovomucoid. In dot assays,
1-µl dots of bacterial suspensions diluted 1:1, 1:10, and 1:50 in
phosphate buffer A were pipetted onto a gridded nitrocellulose paper.
For blot binding analyses, the polyacrylamide gel electrophoresis (16) was used without sodium dodecyl sulfate in order to retain
the pigeon ovomucoid binding activity of the adhesin. Proteins from the
bacterial sonicates were separated in a 6% polyacrylamide gel
electrophoresis in a Bio-Rad Mini Protean II device. The bacterial
extracts in a volume of 75 µl were mixed with 23 µl of sample
solution containing 0.65 M sucrose and 4 mM EDTA in
87 mM Tris-HCl, pH 8.0, and 2 µl of 0.1% bromphenol blue,
and 20 µl of the mixtures were layered into the sample wells. After
electrophoresis, the proteins were transferred electrophoretically to a
PVDF-P membrane (60 mA, 30 min) (17) by using 10 mM CAPS (
)buffer (pH 11):methanol (9:1, v/v). I-pigeon ovomucoid (6
10
cpm/15 cm
, specific activity about
2.5 10 cpm/µg) in phosphate buffer C for 1 h at
+8 °C. The membranes were washed three times for 10 min in
phosphate buffer C, dried between filter papers, and exposed to an
x-ray film with an intensifying screen at -80 °C for
5-48 h.Extraction of Adhesin
Adhesin protein was
extracted from the bacteria by sonicating the bacterial suspension with
an ultrasonic probe in phosphate buffer A five times for 15 s on ice
with a chilling interval of 1-2 min between the sonications.
After sonication, phenylmethylsulfonyl fluoride was added to 2
mM final concentration, and insoluble material was removed by
centrifugation at 15,800 g for 20 min at 8 °C.Ammonium Sulfate Precipitation
The sonication
supernatant (16 ml) was made 60% with respect to ammonium sulfate
saturation by the addition of cold saturated ammonium sulfate (24 ml)
in an ice bath. After 1 h, the resulting pellet was removed by
centrifugation at 15,800 g for 20 min, and the
supernatant was made 70% with respect to ammonium sulfate saturation by
the addition of cold saturated ammonium sulfate (13.3 ml). The pellet
was collected after 1 h by centrifugation and dissolved in 16 ml of
phosphate buffer B (3.3 mM sodium phosphate, 0.05 M
NaCl, pH 7.4), dialyzed overnight at +8 °C against water,
lyophilized, and dissolved in 4 ml of phosphate buffer A.Preparative Gel Electrophoresis
Preparative gel
electrophoresis was performed in the absence of SDS in a Bio-Rad 491
Prep Cell device. The heights of the cylindrical stacking and
separating polyacrylamide gels (6%) were 2 and 6 cm, respectively. The
dialyzed and lyophilized 70% ammonium sulfate pellet (3 ml) was mixed
with 920 µl of sample solution (920 µl) and bromphenol blue (80
µl) and pipetted onto the gel which was run at constant current of
40 mA. The elution buffer was 25 mM Tris-HCl, pH 8.3.
Fractions of 4 ml were collected and analyzed by analytical
electrophoresis in 6% polyacrylamide gels that were stained with Serva
Blue G. Fractions containing the adhesin protein were combined,
dialyzed overnight at +8 °C against phosphate buffer B,
lyophilized, and stored at -20 °C.SDS-Gel Electrophoresis and Isoelectric
Focusing
For gel electrophoresis in the presence of
SDS(16) , the purified adhesin was run in 15% polyacrylamide
gels under reducing and nonreducing conditions. Low Molecular Weight
Standards (Pharmacia, Sweden) were run parallel to the adhesin protein.
Isoelectric focusing was performed in a Phast Gel electrophoresis
device with the Phast isoelectric system (Pharmacia). The Phast Gel
3-9 and the isoelectric focusing standard 3-10 were used.
The gel was stained by using Silver IEF-Method 6 of the Phast
system(18) .Amino Acid Analysis
For the amino acid analysis, 7
nmol of purified adhesin was dissolved in 100 µl of 6 M
HCl. 60 nmol of norleucine was added as an internal standard. The
solution was hydrolyzed at 110 °C for 24 h, lyophilized, and
analyzed with an LKB 4151 Alpha Plus Amino Acid Analyzer according to
the instructions of the manufacturer.Amino Acid Sequencing
The N-terminal amino acid
sequence of the adhesin was determined by Applied Biosystems 477A
Pulsed Liquid Protein/Peptide Sequencer with 120A Amino Acid Analyzer
according to the instructions of the manufacturer. Purified adhesin or
sonicates were subjected to electrophoresis in 6% polyacrylamide gels
and transferred to PVDF-P membranes as described above. The membranes
were stained with Serva Blue for 10 min, and, after destaining of the
extra stain, the adhesin band was cut off for peptide sequencing. The
position of the adhesin was identified by pigeon ovomucoid blotting of
adjacent lanes.Latex-induced Hemagglutination
A suspension of 5
10
latex particles in a volume of 100 µl was
centrifuged at 8000 g for 2.5 min and washed twice
with phosphate buffer A. The particles were suspended into 90 µl of
phosphate buffer A, and 0.4 µg of either purified adhesin or bovine
serum albumin was added in a volume of 10 µl and the suspensions
were incubated for 2 h at room temperature on a tilting table. The
suspensions were centrifuged and washed twice as above. Phosphate
buffer A (45 µl) and bovine serum albumin (5 µl, 5 mg/ml) were
added, and the mixtures were incubated on a tilting table at room
temperature for 1 h. The suspensions were centrifuged and washed twice
as above, and the latex pellets were suspended into 50 µl of
phosphate buffer A. 10 particles) used as controls gave no hemagglutination reactions.
Detection of S. suis Adhesin Activity with Pigeon
Ovomucoid
Pigeon ovomucoid contains blood group P (Gal1-4Gal
1-4GlcNAc1-) terminals on
its glycans(19) . In hemagglutination inhibition studies,
pigeon ovomucoid was shown to be highly active as an inhibitor of the
hemagglutination induced by Gal1-4Gal-binding S. suis(10) . Pigeon ovomucoid was therefore tested as a ligand
for the detection of the adhesin activity in S. suis cells in
a dot binding assay. Radiolabeled pigeon ovomucoid was found to bind
efficiently to S. suis cells with hemagglutination activity,
whereas the nonhemagglutinating control strain did not bind pigeon
ovomucoid (Fig. 1). Furthermore, the binding correlated with the
hemagglutination activity of the strains. Pigeon ovomucoid binding was
subsequently used for the detection of the adhesin activity during
purification of the adhesin from the bacteria.
I-pigeon
ovomucoid and processed for
autoradiography.
Purification of the Adhesin
Several methods used
previously for the extraction of adhesins from bacteria were tried for
the extraction of the S. suis adhesin. These included heat
treatments with or without mechanical homogenization (20, 21) or extraction with lithium
3,5-diiodosalicylate (22) or alkali(23) . These methods
were, however, not suitable for the isolation of the S. suis adhesin. Among the methods tried, sonication with high energy was
the only successful method for detaching the adhesin from S. suis cells.
I-labeled pigeon ovomucoid (B).
Characterization of the Purified Adhesin
The
purified adhesin appeared in SDS-polyacrylamide gel electrophoresis as
a single homogeneous band of an apparent size of 18 kDa (Fig. 4A). The mobility was not changed by the use of a
reducing agent, which suggested the absence of disulfide bridges. This
was also confirmed by amino acid analysis which revealed the absence of
cysteine residues (Table 1). The amino acid composition indicated
that the adhesin is rich in glutamic acid and glycine and also contains
high concentrations of alanine and lysine. The adhesin contained
somewhat more acidic (21.7%) than basic (16.0%) residues and a
relatively high proportion of hybrofobic amino acids (40.3%). The
isoelectric point of the purified adhesin was 6.4 (Fig. 4B). The N-terminal amino acid sequence
Ala-Ser-Pro-Ala-Glu-Ile-Ala-Ser-Phe-Ser-Pro-Ala-Pro- was revealed by
sequencing of the purified adhesin. The sequence had no apparent
sequence similarity with other bacterial adhesins or surface proteins
of Gram-positive bacteria (The NCBI BLAST data base, 8/95).
and P differing in
their Gal1-4Gal binding specificity(11) . The N
termini of adhesins determined from electrophoretic blots of four other S. suis strains, two of type P (TEW/2, R75/L1) and
two of type P (752, 825), were identical with the purified
adhesin.Correlation of Amount of Adhesin with Hemagglutinating
Activity
In order to investigate whether the varying
hemagglutination activities of different S. suis strains could
be explained by the expression of variable amounts of the adhesin,
sonicates of these strains were subjected to nondenaturing gel
electrophoresis, and the presence of the adhesin was probed by blotting
with radiolabeled pigeon ovomucoid (Fig. 5). One single band
with a mobility corresponding to the purified adhesin was detected in
all strains. There was no apparent difference in the band mobilities of
P (strains 628, TEW/2, and R75/L1) and P (strains 836, 752, 825, and 3031) adhesins.
I-labeled pigeon ovomucoid. The hemagglutinating
activities are given as the reciprocal of the titer (bottom).
Bacteria of strain 628 extracted in high or low hemagglutination titer
phases were included in the analysis.
Agglutination Activity of the Purified Adhesin
The
purified adhesin expressed only weak hemagglutination activity,
presumably due to its monovalent nature. In order to make the adhesin
polyvalent, it was adsorbed onto latex particles. A strong
hemagglutination reaction was achieved with sialidase-erythrocytes on a
glass slide (Table 2). As compared to the free adhesin, 0.2
µg of which agglutinated sialidase-treated human erythrocytes on a
microtiter plate weakly with a titer of 1:1, 0.2 µg of the adhesin
adsorbed to latex particles hemagglutinated the erythrocytes with a
titer of 1:16. No agglutination was achieved with latex particles
coated with bovine serum albumin. On the other hand, the
hemagglutination induced by the adhesin-bound latex particles was
inhibited specifically with the same inhibitory compounds, galactose, N-acetylgalactosamine, and pigeon ovomucoid as
hemagglutination induced by whole bacteria(10, 11) .
1-4Gal-containing blood group P active glycans, is an effective inhibitor of the P adhesins of S. suis(10, 11) . This glycoprotein was
therefore used as an indicator for the presence of the adhesin in S. suis cells by dot binding assay and for the identification
of the adhesin protein during its purification. Different lines of
observations suggest that the protein isolated was indeed the adhesin
responsible for the hemagglutinating activity of the bacteria. The
hemagglutination activity correlated with pigeon ovomucoid binding both
in whole cells and in the sonication extracts of the cells. In the
latter, only one pigeon ovomucoid-binding component was present and
corresponded in mobility to the purified protein. Furthermore, the
purified protein adsorbed to latex particles induced hemagglutination,
which was inhibited by the same inhibitory compounds as agglutination
induced by the intact bacteria.1-Gal-binding S. suis, the adhesion
activity inhibitable by galactose and N-acetylgalactosamine
(type P) or by galactose only (type
P)(11) . In the present study, the adhesin was
isolated from strain 628 which is of type P. However,
pigeon ovomucoid also bound to whole bacteria and the adhesin band of
type P bacteria. Furthermore, the adhesin bands of
P and P had similar mobilities in gel
electrophoresis, and their N-terminal amino acid sequences were
identical. These findings indicate that the two variant P adhesins are
closely related. No homology to previously known adhesins was apparent. 1-4Gal-binding adhesins from
Gram-positive bacteria and from bacteria associated with meningitis.
Among Gram-negative bacteria, extraintestinal E. coli strains
that cause urinary tract infections frequently produce P-fimbrial
adhesins as virulence factors (37, 38) . These
adhesins interact with glycolipids containing the Gal1-4Gal
structure. On the other hand, E. coli isolates associated with
newborn meningitis contain S-fimbrial adhesins recognizing
Sia2-3Gal(33, 39) . Sia2-3Gal binding
has also been described in S. suis, but the adhesion activity
differs from that of E. coli in the recognition of the inner
sugars in the receptor oligosaccharide(40) . In pigs, many
tissues express Gal1-4Gal-containing
glycolipids(41) , and these are able to serve as binding
ligands for S. suis containing P adhesin to frozen sections of
pig pharyngeal tissue(10) . However, the in vivo roles
of the different adhesion specificities remain so far unresolved.
Identification and purification of the P adhesin of S. suis will now make possible the cloning of the corresponding gene and
thus facilitate studies designed to elucidate the molecular mechanism
of the binding interaction, the basis of the differential binding of
the variant adhesins, and the pathogenic role of the adhesin.
)
We thank Dr. H. C. Zanen, Dr. F. Clifton-Hadley, and
Dr. J. Hommez for bacterial strains and T. Taskinen for technical
assistance.
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
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