Ras-related protein Rab-3D （RAB3D） belongs to the Ras superfamily of small Rab GTPases. Rab proteins play a vital role for， either in endocytosis or in biosynthetic protein transport. Rab3D mRNA is primarily expressed in white adipose tissue and， coincident with GLUT4， increases upon differentiation of 3T3-L1 fibroblasts into insulin-responsive adipocytes. Rab3D exhibits close structural similarities with Rab 3A， an isoform which is functionally associated with regulated exocytosis in various cell types.
