9.A.78. The Retinal Degeneration B Protein (RdgB) Family
RdgB catalyzes the transfer of phosphatidylinositol (PI) and phosphatidic acid (PA) between membranes (Garner et al. 2012). It may control the phosphatidylinositol concentration in transport vesicles from the subrhabdomeric cisternae (SRC) to the rhabdomere (Vihtelic et al. 1991) and may also function as a calcium transporter (Vihtelic et al. 1991). Eukaryotic proteins containing a phosphatidylinositol transfer (PITP) domain can be divided into two groups, one consisting of small soluble 35-kDa proteins and the other that are membrane- associated and show sequence similarities to the Drosophila retinal degeneration B (rdgB) protein. The rdgB protein consists of four domains, an amino terminal PITP domain, a Ca2+-binding domain, a transmembrane domain and a carboxyl terminal domain that interacts with the protein tyrosine kinase, PYK2. Three mammalian phosphatidylinositol transfer protein membrane-associated genes (PITPNM1, 2 and 3) with homology to Drosophila rdgB have been described and are expressed in the mammalian retina. The rdgB gene plays a critical role in the invertebrate phototransduction pathway, and homologous genes are considered as candidate genes for human eye diseases. Phylogenetic analysis indicates that the human genes arose by gene duplication that occurred very early in animal evolution (Ocaka et al. 2005).