Three homologs of rds/peripherin in Xenopus laevis photoreceptors that exhibit covalent and non-covalent interactions.

We have isolated and characterized three homologs of mammalian rds/peripherin from Xenopus retinae. One (xrds38) is likely the Xenopus ortholog, while the other two (xrds36 and -35) are more distant relatives. By immunocytochemical analysis of retinal sections, xrds38 is distributed in both rod and cone photoreceptors, while xrds36 and xrds35 are present in rods only. At the EM level, xrds38 is present specifically in the rims and incisures of rod and cone outer segment discs. All are N-glycosylated and form covalent dimers. Immunoprecipitation analysis showed that in rods, these three proteins interact to form heterotetrameric or higher-order complexes. The pattern of sequence conservation among the xrds proteins, mammalian rds/peripherin, and mammalian rom-1 suggest that the central portion of the intradiscal D2 loop contains the interacting structural elements.