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K. Cho, M.R. Guruju, P.A. Ferreira; Molecular Dissection of RPGRIP1 Interactome . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3747.
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© ARVO (1962-2015); The Authors (2016-present)
The RPGRIP1 locus encodes several isoforms of the Retinitis Pigmentosa GTPase Regulator–Interacting Protein 1 (RPGRIP1). Mutations in RPGRIP1 cause Leber congenital amaurosis (LCA). RPGRIP1α1 isoform is a multimodular and scaffold protein, which contains four structural/functional modules. Human and bovine photoreceptors express only RPGRIP1α1. The Retinitis Pigmentosa GTPase Regulator (RPGR) protein, which causes XlRP3, interacts with the RPGR–interacting domain (RID) of RPGRIP1, while nephrocystin–4 (NPHP4), which causes Senior–Løken syndrome, associates with the C2 domain of RPGRIP1. The concert action of these domains strongly modulates the dynamic subcellular localization of RPGRIP1 and domains thereof, and the limited proteolytic processing of RPGRIP1α1. Yet, the role of the N–terminal domain of RPGRIP1 and the impact of human mutations in RPGR isoforms on RPGRIP1α1 processing and targeting remain elusive. The current study aims at i) characterizing all XlRP3–missense mutations in RPGR, ii) their impact on RPGRIP1 activity and iii) the function of the N–terminal domain of RPGRIP1α1.
We employed a combination of yeast interaction–trap screens, mutagenesis analysis, immuno– and cell–culture assays, and mouse genetics to evaluate the previously described aims.
We found that mutations in RPGR isoforms can be classified in five different classes based, among other factors, on the severity of the impairment of the interaction between RPGR and RPGRIP1, location of the mutations, and phenotypes observed. Four novel partners of RPGRIP1 were identified and these interact with its N–terminal domain. These partners mediate protein targeting and stabilization, protein processing and modulation of RNA processing. Structure–function analysis is underway to delimit the boundary domains of the interaction between these partners and RPGRIP1.
The data support that the C–terminal domains of RPGRIP1 behave as a tissue–selective effector and scaffold for RPGR and NPHP4, they determine the dynamic subcellular localization of RPGRIP1 and likely suppress the pathobiological properties of RPGRIP1. In contrast, the N–terminal domain links tissue–selective pathways with ubiquitous cellular functions that are mediated by the novel partners identified and these may confer the pathophysiological properties to the RPGRIP1 interactome upon mutations in RPGRIP1, NPHP–4 and RPGR.
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