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Andrew F X Goldberg, Linda M. Ritter, Nidhi Khattree; Structure-function analysis of the peripherin-2/rds cytoplasmic C-terminal domain. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4659.
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© ARVO (1962-2015); The Authors (2016-present)
<br /> A variety of inherited retinal diseases are caused by defects in peripherin-2/rds (P/rds), an integral membrane protein essential for proper formation of the outer segment (OS) membranes of rod and cone photoreceptors. Although a variety of pathogenic mutations are located within the protein's C-terminus, the normal function of this domain is not known and the means by which mutations cause retinal degenerations are not understood. The current study investigates the importance of an inducible amphipathic helix (AH) located within this critical region.
Expression vectors for WT P/rds and a mutant lacking the inducible AH (P/rdsΔAH) were constructed and used to obtain moderately expressing clonal HEK293 cell lines and transgenic X. laevis, using antibiotic selection and I-SceI transgenesis respectively. Western blotting, ICC, IHC, LSCM, and TEM, were applied to the HEK293 lines and transgenic frog retinas to characterize biosynthesis, subunit assembly, localization, and membrane shaping activity of the P/rdsΔAH mutant relative to WT P/rds.
The P/rdsΔAH deletion mutant is properly folded and assembled into non-covalent tetrameric complexes and polymeric chains of disulfide-bonded tetramers in HEK293. This mutant, like WT P/rds, is largely released from the cellular secretory pathway and accumulates within a distinct set of intracellular membranes. TEM analysis finds that the P/rdsΔAH mutant, like WT P/rds, induces networks of high curvature tubulo-vesicular membrane in stably expressing HEK293 cells. When expressed in transgenic X. laevis, the P/rdsΔAH mutant is efficiently trafficked from its inner segment site of biosynthesis to its OS site of function in a manner similar to WT.
We find that the inducible AH in the P/rds C-terminus is not required for protein biosynthesis, subunit assembly, disulfide-mediated tetramer polymerization, generation of high curvature membranes, or trafficking to rod OSs in vivo. Since we previously found that a peptide mimetic of the AH alone can induce high curvature membranes in vitro, but current results show that this feature is not essential for P/rds induction of highly curved membranes in celluo, the new findings raise the question of whether this AH functions in concert with other protein domains for generating membrane curvature, or whether it plays an alternative primary role.
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