Photoreceptor Synaptic Protein HRG4(UNC119) Interacts With ARL2 via a Putative Conserved Domain

Abstract

Abstract: : Purpose: HRG4(UNC119) is a photoreceptor synaptic protein of unknown function, shown when mutated to cause retinal degeneration in a patient and in a confirmatory transgenic model. ADP-ribosylation factor-like protein 2 (ARL2) was identified as an interactor of HRG4 by the yeast two-hybrid strategy. Phosphodiesterase δ (PDEδ) is homologous to HRG4 and also interacts with ARL2. In this study, we subjected HRG4 to further studies to confirm its interaction with ARL2 and to assess its similarity to PDEδ in regard to its possible function. Methods: The presence of ARL2 in the retina and co-localization with HRG4 was investigated by Western blot and double immunofluorescence analysis, respectively. The interaction of ARL2 with HRG4 was confirmed by co-immunoprecipitation and direct binding analysis. The structural features of PDEδ shown to be important for its interaction with ARL2 were compared to that present in HRG4. Results: The presence of ARL2 in the retina and co-localization with HRG4 was confirmed by Western blot and double immunofluorescence analysis, respectively. The interaction of ARL2 with HRG4 was further confirmed by co-immunoprecipitation and direct binding analysis. Amino acid residues of PDEδ involved in binding ARL2 and forming a hydrophobic pocket were shown to be highly conserved in HRG4. Conclusions: The interaction of ARL2 with HRG4 and their co-localization in the appropriate layers of the retina were confirmed, supporting their functional significance in the retina. The significant structural similarity between HRG4 and PDEδ in the regions involved in ARL2 binding and hydrophobic pocket formation suggested similarity in binding mechanism and function.

Keywords: molecular biology • retina • protein structure/function