title: [Study of the molecular organization of visual rhodopsin in photoreceptor membranes by limited proteolysis].
abstract: Proteolysis of rhodopsin in disc membranes of right-side out orientation by thermolysin, papain and St. aureus V8 protease allowed to identify two highly exposed regions of polypeptide chain located on the cytoplasmic membrane surface: carboxyl terminal sequence 321-348 and the fragment 236-241. Incubation with chymotrypsin reveals the third site on the cytoplasmic surface, 146-147, accessible to proteolytic enzymes. Frozen-thawed membranes comprise a mixture of vesicles with normal and inverted orientation. Both thermolytic and chymotryptic digests of rhodopsin in these membranes contain the polypeptide which represents the amino terminal sequence lacking the first 30 amino acid residues. Thus at least 30 amino acids from the N-terminus must protrude into the intradiscal space. One additional site was located on the intradiscal surface: papain digests rhodopsin in the inverted membranes at the position 186-187. Localization of the proteolytic cleavage sites allowed to propose a model for rhodopsin topography in disc membrane: the polypeptide chain traverses the bilayer thickness seven times; each of seven transmembrane segments containing approximately 40 amino acid residues includes a sequence of approximately 30 hydrophobic amino acids; which are probably in close contact with hydrocarbon matrix of the membrane. Hydrophobic sequences are terminated with fragments containing clusters of hydrophilic amino acids, possibly interacting with lipid polar head groups and orienting each segment in the bilayer.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002462:Cell Membrane; D002918:Chymotrypsin; D006868:Hydrolysis; D010786:Photoreceptor Cells / Q000648:ultrastructure; D011487:Protein Conformation; D012168:Retinal Pigments; D012243:Rhodopsin; D012374:Rod Cell Outer Segment / Q000648:ultrastructure
chemical_list: D012168:Retinal Pigments; D012243:Rhodopsin; D002918:Chymotrypsin
vernacular_title: Issledovanie molekuliarnoĭ organizatsii zritel'nogo rodopsina v fotoretseptornykh membranakh metodom ogranichennogo proteinoliza.