Anti-VPS33B late endosome and lysosome associated antibodies are used for the immunodetection of the protein encoded by the VPS33B gene. In humans, the canonical protein has a reported length of 617 amino acid residues and a mass of 70.6 kDa. Its subcellular localization is in the cytoplasmic vesicles, lysosomes, and membrane. Alternative splicing is reported to yield 2 different isoforms for this protein. It is widely expressed across many tissue types. A member of the STXBP/unc-18/SEC1 protein family, it is believed to play a role in vesicle-mediated protein trafficking to lysosomal compartments and in membrane docking/fusion reactions of late endosomes/lysosomes. Post-translational modifications have been described, including phosphorylation. Other names for this target antigen include PFIC12, vacuolar protein sorting-associated protein 33B, vacuolar protein sorting 33 homolog B, vacuolar protein sorting 33-like protein B, and KDIDAR. Gene orthologs have been identified in the mouse, rat, bovine, frog, zebrafish, chimpanzee and chicken species.