title: Molecular characterization of peripherin-2 and rom-1 mutants responsible for digenic retinitis pigmentosa.
abstract: Peripherin-2 and Rom-1 are homologous tetraspanning membrane proteins that assemble into noncovalent tetramers and higher order disulfide-linked oligomers implicated in photoreceptor disc morphogenesis. Individuals who coinherit a L185P peripherin-2 mutation and a null or G113E rom-1 mutation are afflicted with retinitis pigmentosa, whereas individuals who inherit only one defective gene are normal. We examined the expression, subunit assembly, and disulfide-mediated oligomerization of L185P and L185A peripherin-2 and L188P Rom-1 by velocity sedimentation, co-immunoprecipitation, and cross-linking. These mutants formed noncovalent dimers under disulfide-reducing conditions but failed to assemble into core tetramers. Under nonreducing conditions, L185P dimers formed disulfide-linked tetramers but not higher order oligomers. L185P coassembled with wild-type peripherin-2 and Rom-1 to form tetramers and higher order disulfide-linked oligomers characteristic of the wild-type proteins. The G113E Rom-1 mutant expressed 20-fold lower than wild-type Rom-1, indicating that it behaves mechanistically as a null allele. We conclude that Leu(185) of peripherin-2 (Leu(188) of Rom-1) is critical for tetramer but not dimer formation and that the core tetramer has 2-fold symmetry. Peripherin-2-containing tetramers are required for higher order disulfide-linked oligomer formation. The level of these oligomers is critical for stable photoreceptor disc formation and the digenic retinitis pigmentosa disease phenotype.
authors: Department of Biochemistry and Molecular Biology and Department of Ophthalmology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors: C J
authors: CJ
authors: Loewen
authors: O L
authors: OL
authors: Moritz
authors: R S
authors: RS
authors: Molday
mesh_terms: D000818:Animals; D019556:COS Cells; D005136:Eye Proteins / Q000235:genetics / Q000502:physiology*; D005799:Genes, Dominant; D006720:Homozygote; D006801:Humans; D007381:Intermediate Filament Proteins / Q000235:genetics / Q000502:physiology*; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008970:Molecular Weight; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D064531:Peripherins; D012174:Retinitis Pigmentosa / Q000235:genetics*; D059470:Tetraspanins
chemical_list: D005136:Eye Proteins; D007381:Intermediate Filament Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C578994:PRPH protein, human; D064531:Peripherins; C513106:ROM1 protein, human; D059470:Tetraspanins