1.A.38 The Golgi pH Regulator (GPHR) Family
The organelles within secretory and endocytotic pathways in mammalian cells have acidified lumens, and regulation of their acidic pH is critical for the trafficking, processing and glycosylation of cargo proteins and lipids, as well as the morphological integrity of the organelles. Maeda et al. (2008) described a novel protein involved in Golgi acidification. Mutant cells defective in Golgi acidification exhibited delayed protein transport, impaired glycosylation and Golgi disorganization. Using expression cloning, a novel Golgi-resident multi-transmembrane protein, named Golgi pH regulator (GPHR), was identified. After reconstitution in planar lipid bilayers, GPHR exhibited voltage-dependent anion-channel activity that may function in counterion conductance. Thus, GPHR modulates Golgi functions through regulation of acidification. It is reported to be homologous to the G-protein coupled receptor 89B of humans (NP_057418). Its function is reviewed by Edwards and Kahl (2010). It has a central DUF3735 domain, a C-terminal ABA_GREP domain, and 9 putative TMSs.