Lipid-binding and transfer protein essential for lysosomal degradation of ganglioside GM2. Extracts single GM2 molecules from intralysosomal luminal vesicle (ILV) membranes and presents them in soluble form to beta-hexosaminidase A (HEXA) for cleavage of N-acetyl- D-galactosamine and conversion to GM3 (PubMed:30988135, PubMed:8900233). Forms a stoichiometric GM2-GM2A complex that serves as the substrate for HEXA (PubMed:30988135, PubMed:8900233). Also stimulates the breakdown of glycolipid GA2 by HEXA (By similarity). Possesses dual function: membrane lipid mobilization/solubilization and lipid substrate presentation to hydrolases (PubMed:30988135). The large binding pocket can accommodate several single-chain phospholipids and fatty acids (By similarity). Exhibits some calcium-independent phospholipase activity (By similarity). Participates in cholesterol transfer (PubMed:17552909). {ECO:0000250|UniProtKB:Q60648, ECO:0000269|PubMed:17552909, ECO:0000269|PubMed:30988135, ECO:0000269|PubMed:8900233}. This is the function of ENSG00000196743 (GM2A, ganglioside GM2 activator).