[Bis(monoacylglycero)phosphate synthase CLN5, secreted form]: Catalyzes the synthesis of bis(monoacylglycero)phosphate (BMP) via transacylation of 2 molecules of lysophosphatidylglycerol (LPG) (PubMed:37708259). BMP also known as lysobisphosphatidic acid plays a key role in the formation of intraluminal vesicles and in maintaining intracellular cholesterol homeostasis (PubMed:37708259). Can use only LPG as the exclusive lysophospholipid acyl donor for base exchange and displays BMP synthase activity towards various LPGs (LPG 14:0, LPG 16:0, LPG 18:0, LPG 18:1) with a higher preference for longer chain lengths (PubMed:37708259). Plays a role in influencing the retrograde trafficking of lysosomal sorting receptors SORT1 and IGF2R from the endosomes to the trans-Golgi network by controlling the recruitment of retromer complex to the endosomal membrane (PubMed:22431521). Regulates the localization and activation of RAB7A which is required to recruit the retromer complex to the endosomal membrane (PubMed:22431521). . Exhibits palmitoyl protein thioesterase (S-depalmitoylation) activity in vitro and most likely plays a role in protein S- depalmitoylation. . This is the function of ENSG00000102805 (CLN5, CLN5 lysosomal BMP synthase).