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J Biol Chem, Vol. 274, Issue 30, 21437-21442, July 23, 1999
From the Center for Advanced Research in Biotechnology, National
Institute of Standards and Technology and the University of
Maryland Biotechnology Institute, Rockville, Maryland 20850
Previous studies on bovine opsin folding and
assembly have identified an amino-terminal fragment, EF(1-232), which
folds and inserts into a membrane only after coexpression with its
complementary carboxyl-terminal fragment, EF(233-348). To further
characterize this interaction, EF(1-232) production was examined upon
coexpression with carboxyl-terminal fragments of varying length and/or
amino acid composition. These included fragments with incremental
deletions of the third cytoplasmic loop (TH(241-348) and
EF(249-348)), a fragment composed of the third cytoplasmic loop and
sixth transmembrane helix (HF(233-280)), a fragment composed of the
sixth and seventh transmembrane helices (FG(249-312)), and
EF(233-348) and TH(241-348) fragments with Pro-267 or Trp-265
mutations. Although EF(1-232) production was independent of the third
cytoplasmic loop and carboxyl-terminal tail, both the sixth and seventh
transmembrane helices were essential. The effects of mutations in the
sixth transmembrane helix on EF(1-232) expression were dependent on
the length of the third cytoplasmic loop. Although Pro-267 mutations in
EF(233-348) failed to stabilize EF(1-232) expression, their
introduction into TH(241-348) was without discernible effects.
However, Trp-265 substitutions in the EF(233-348) and TH(241-348)
fragments conferred significant EF(1-232) production. Therefore, key
residues in the transmembrane helices may exert their effects on opsin
folding, assembly, and/or function by influencing the conformation of
the connecting loops.
Folding and Assembly in Rhodopsin
EFFECT OF MUTATIONS IN THE SIXTH TRANSMEMBRANE HELIX ON THE
CONFORMATION OF THE THIRD CYTOPLASMIC LOOP
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.
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