Small G-protein signalling modulator 1/2 (also known as RUTBC2/1) bind to Rab9A via their Pleckstrin homology (PH) domain [, ]. RUTBC1 stimulates GTP hydrolysis by Rab32 and Rab33B [], while RUTBC2 appears to be a GAP for Rab36, Rab9A and associated proteins controling the recycling of mannose-6-phosphate receptors from late endosomes to the trans-Golgi [, , ]. This entry represents the PH domain of RUTBC1/2.
This domain adopts a PH-like fold. It has been called the Rab-binding domain (RBD) []. Small G-protein signalling modulator 1/2 (also known as RUTBC2/1) bind to Rab9A via their Pleckstrin homology (PH) domain [, ]. RUTBC1 stimulates GTP hydrolysis by Rab32 and Rab33B [], while RUTBC2 appears to be a GAP for Rab36, Rab9A and associated proteins controling the recycling of mannose-6-phosphate receptors from late endosomes to the trans-Golgi [, , ].
Ras-related protein Rab33 is a member of the large Rab GTPase family. Rab33B is ubiquitously expressed in mouse tissues and cells, where it is localized to the medial Golgi cisternae. It colocalizes with alpha-mannose II. Together with the other cisternal Rabs, Rab6A and Rab6A', it is believed to regulate the Golgi response to stress and is likely a molecular target in stress-activated signaling pathways []. Rab33A (previously known as S10) is expressed primarily in the brain and immune system cells. In humans, it is located on the X chromosome at Xq26 and its expression is down-regulated in tuberculosis patients. Experimental evidence suggests that Rab33A is a novel CD8+ T cell factor that likely plays a role in tuberculosis disease processes []. Rabs are regulated by GTPase activating proteins (GAPs), which interact with GTP-bound Rab and accelerate the hydrolysis of GTP to GDP. Guanine nucleotide exchange factors (GEFs) interact with GDP-bound Rabs to promote the formation of the GTP-bound state. Rabs are further regulated by guanine nucleotide dissociation inhibitors (GDIs), which facilitate Rab recycling by masking C-terminal lipid binding and promoting cytosolic localization. Most Rab GTPases contain a lipid modification site at the C terminus, with sequence motifs CC, CXC, or CCX. Lipid binding is essential for membrane attachment, a key feature of most Rab proteins [, ].
