Multiprotein complexes of Retinitis Pigmentosa GTPase regulator (RPGR), a ciliary protein mutated in X-linked Retinitis Pigmentosa (XLRP)

Abstract

Mutations in Retinitis Pigmentosa GTPase Regulator (RPGR) are a frequent cause of X-linked Retinitis Pigmentosa (XLRP). The RPGR gene undergoes extensive alternative splicing and encodes for distinct protein isoforms in the retina. Extensive studies using isoform-specific antibodies and mouse mutants have revealed that RPGR predominantly localizes to the transition zone to primary cilia and associates with selected ciliary and microtubule-associated assemblies in photoreceptors. In this chapter, we have summarized recent advances on understanding the role of RPGR in photoreceptor protein trafficking. We also provide new evidence that suggests the existence of discrete RPGR multiprotein complexes in photoreceptors. Piecing together the RPGR-interactome in different subcellular compartments should provide critical insights into the role of alternative RPGR isoforms in associated orphan and syndromic retinal degenerative diseases.

Fig. 13.1

(a) Schematic representation of the strategy to dissect distinct RPGR-containing multiprotein complexes in photoreceptor cilia. IP: Immunoprecipitation; Ab: antibody, (b) Protein extract (~150 µg) was subjected to immunoprecipitation using indicated antibodies. The precipitated beads (Pellet) and supernatant (Sup) were analyzed by SDS-PAGE and immunoblotting (IB) using same antibodies. No signal in the supernatant indicates sufficient immunodepletion of the respective proteins from the extract. (c) and (d) CEP290 – or SMC1 – immunodepleted (ID) extract was subjected to IP using RPGR antibody or rabbit IgG (immunoglobulin) followed by SDS-PAGE and immunoblotting (IB) using indicated antibodies

Fig. 13.2

Schematic representation of the putative distinct RPGR complexes that can exist in photoreceptors. Proteins A and B represent as yet unidentified molecular partners that can be part of such complexes