Identification and subcellular localization of human rab5b, a new member of the ras-related superfamily of GTPases.

Abstract

Members of the mammalian rab family of GTPases are associated with specific subcellular compartments, where these proteins are postulated to function in vesicular transport. By screening a human umbilical vein endothelial cell library with degenerate oligonucleotide probes, we have isolated a 1.6-kb cDNA clone encoding a 215-amino-acid protein belonging to the rab family of GTPases. This newly identified rab protein is 81% identical to human rab5, the canine counterpart of which has been localized to the plasma membrane and early endosomes. In light of this homology, we have named this new member of the GTPase superfamily "rab5b." Northern analysis using the rab5b cDNA as a probe revealed a 3.6-kb mRNA in a variety of cell types, including human umbilical vein endothelial cells, K562 erythroleukemia cells, U937 monoblastic cells, and HeLa cells. A fusion protein between glutathione-Stransferase (GST) and rab5b was expressed in bacteria and purified to homogeneity. The recombinant protein was shown to bind GTP and GDP. As is typical of other recombinant rab proteins, the rab5b-GST fusion protein displayed a low intrinsic rate of GTP hydrolysis (0.005/min). An antiserum to rab5b was prepared and used to determine the apparent molecular size and subcellular distribution of the protein. Western blotting with this antibody revealed a 25-kD protein in COS cells transfected with rab5b and in nontransfected HeLa cells. Indirect immunofluorescence and subcellular fractionation showed that rab5b localizes to the plasma membrane. We speculate that rab5b plays a role in vesicular trafficking at the plasma membrane in various cell types. (J. Clin. Invest. 1992Invest. .89:996-1005

A Novel Susceptibility Locus for Type 1 Diabetes on Chr12q13 Identified by a Genome-Wide Association Study

“…3). RAB5B (MIM:179514) encodes a member of the RAS oncogene family that may be involved in vesicular trafficking at the plasma membrane (17). SUOX (MIM:606887) encodes a liver-specific sulfite oxidase involved in the degradation of sulfur-containing amino acids.…”

Co‐operative regulation of endocytosis by three RAB5 isoforms

“…The amplification products of the second PCR were subcloned into pGEM1. The amino acid sequence of mouse Rab5b was found to be 100% identical to human Rab5b [22].…”

“…The protein is essential for in vitro homotypic fusion of early endosomes and is able to increase the rate of endocytosis in vivo when overexpressed [19,20]. It has recently being renamed Rab5a since the discovery of two partial cDNA clones highly related that were then called Rab5b and Rab5c [21,22]. This indicated the presence of a subgroup of at least three Rab5 protein in mammalian cells.…”

Tyrphostin A8 stimulates a novel trafficking pathway of apically endocytosed transferrin through Rab11-enriched compartments in Caco-2 cells

“…The cells were grown in DMEM (Invitrogen) supplemented with 50 U/ml penicillin, 50 g/ml streptomycin, nonessential amino acids, L-glutamine, and FBS (10%). Localization Plasma membrane, clathrin-coated vesicles, early endosomes (4,6,55) Pericentriolar recycling endosome in nonpolarized cells (14,37,48), apical recycling endosome in Caco-2 and MDCK cells (5,53), trans-Golgi network (7, 49) Function…”