The first and second cytoplasmic loops of the G-protein receptor, rhodopsin, independently form beta-turns.
The cytoplasmic face of the transmembrane protein, rhodopsin, is made up of one carboxyl terminal and three cytoplasmic loops connecting six of the seven transmembrane helices. Neither the high-resolution, three-dimensional structure of this G-protein receptor nor any other cell surface receptor is known. In this work, the structures of peptides containing the amino acid sequence of the first and second cytoplasmic loops of rhodopsin have been determined. Both loops show ordered structures in solution. In both loops, the ends of the transmembrane helices unwind and form a beta-turn. The conformations of the two loops are remarkably similar, even though their sequences are not. These data suggest a structural motif for short loops in transmembrane proteins. The well-ordered structures of these loops, in the absence of the transmembrane helices, indicate that the primary sequences of these loops stabilize the beta-turn. These data further suggest that the loops may contribute to the folding of such membrane proteins during their synthesis and insertion into membranes.
Yeagle
P L
PL
Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo 14214, USA.
Alderfer
J L
JL
Salloum
A C
AC
Ali
L
L
Albert
A D
AD
D000818:Animals; D002417:Cattle; D019204:GTP-Binding Proteins / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D017433:Protein Structure, Secondary; D011956:Receptors, Cell Surface / Q000737:chemistry; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism; D015293:Transducin / Q000037:antagonists & inhibitors
D008565:Membrane Proteins; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; D012243:Rhodopsin; D019204:GTP-Binding Proteins; D015293:Transducin