The role of subunit assembly in peripherin-2 targeting to rod photoreceptor disk membranes and retinitis pigmentosa.
Peripherin-2 is a member of the tetraspanin family of membrane proteins that plays a critical role in photoreceptor outer segment disk morphogenesis. Mutations in peripherin-2 are responsible for various retinal degenerative diseases including autosomal dominant retinitis pigmentosa (ADRP). To identify determinants required for peripherin-2 targeting to disk membranes and elucidate mechanisms underlying ADRP, we have generated transgenic Xenopus tadpoles expressing wild-type and ADRP-linked peripherin-2 mutants as green fluorescent fusion proteins in rod photoreceptors. Wild-type peripherin-2 and P216L and C150S mutants, which assemble as tetramers, targeted to disk membranes as visualized by confocal and electron microscopy. In contrast the C214S and L185P mutants, which form homodimers, but not tetramers, were retained in the rod inner segment. Only the P216L disease mutant induced photoreceptor degeneration. These results indicate that tetramerization is required for peripherin-2 targeting and incorporation into disk membranes. Tetramerization-defective mutants cause ADRP through a deficiency in wild-type peripherin-2, whereas tetramerization-competent P216L peripherin-2 causes ADRP through a dominant negative effect, possibly arising from the introduction of a new oligosaccharide chain that destabilizes disks. Our results further indicate that a checkpoint between the photoreceptor inner and outer segments allows only correctly assembled peripherin-2 tetramers to be incorporated into nascent disk membranes.
Loewen
Christopher J R
CJ
Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3.
Moritz
Orson L
OL
Tam
Beatrice M
BM
Papermaster
David S
DS
Molday
Robert S
RS
D000818:Animals; D030801:Animals, Genetically Modified; D019556:COS Cells; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D049452:Green Fluorescent Proteins; D007381:Intermediate Filament Proteins / Q000378:metabolism*; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D064531:Peripherins; D021122:Protein Subunits / Q000378:metabolism; D012174:Retinitis Pigmentosa / Q000235:genetics / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D029867:Xenopus Proteins; D014982:Xenopus laevis
D007381:Intermediate Filament Proteins; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C578995:PRPH protein, Xenopus; D064531:Peripherins; D021122:Protein Subunits; D029867:Xenopus Proteins; D049452:Green Fluorescent Proteins