| Type: | Family | Name: | BLOC-2 complex, Hps5 subunit |
| Description: | Lysosome-related organelles comprise a group of specialised intracellular compartments that include melanosomes and platelet dense granules in mammals and eye pigment granules in insects. Genes associated with HPS encode subunits of three complexes of unknown function; (BLOC)-1, -2 and -3 []. Hermansky-Pudlak syndrome (HPS) is a disorder of lysosome-related organelle biogenesis. There are eight known HPS proteins of the BLOCs (Biogenesis of Lysosome-related Organelles Complex) []. Organelles affected in HPS include the melanosome, resulting in hypopigmentation, and the platelet delta (dense) granule, resulting in prolonged bleeding times. HPS in humans or mice is caused by mutations in any of 15 genes, five of which encode subunits BLOC-1. BLOC-1 and BLOC-2 act sequentially in the same pathway. Melanosome maturation requires at least two cargo transport pathways directly from early endosomes to melanosomes. One pathway mediated by AP-3, and one pathway mediated by BLOC-1 and BLOC-2 []. The adaptor protein AP-3 complex is a component of the cellular machinery that controls protein sorting from endosomes to lysosomes and melanosomes. BLOC-1 interacts physically and functionally with AP-3 to facilitate the trafficking of a known AP-3 cargo, CD63, and of tyrosinase-related protein 1 (Tyrp1). BLOC-1 also interacts with BLOC-2 to facilitate Tyrp1 trafficking by a mechanism apparently independent of AP-3 function. Both BLOC-1 and -2 predominantly localise to early endosome-associated tubules [].Complex-2 (BLOC-2) contains the HPS3, HPS5 and HPS6 proteins as subunits. Fibroblasts deficient in the BLOC-2 subunits HPS3 or HPS6 have normal basal secretion function of the lysosomal enzyme beta-hexosaminidase [].HPS-5 results from deficiency of the HPS5 protein, a component of BLOC-2 []. This group represents a BLOC-2 complex, Hps5 subunit. | Short Name: | BLOC-2_complex_Hps5_subunit |
