BLOC1S2 encodes a subunit of the BLOC-1 complex, a hetero-octameric protein assembly with a distinctive arc-shaped architecture composed of two hemicomplexes 1. As a component of BLOC-1, BLOC1S2 is essential for biogenesis of lysosome-related organelles (LROs) including platelet dense granules and melanosomes 1. BLOC1S2 also participates in the BORC complex, which recruits motor proteins to lysosomes for microtubule-directed transport and peripheral localization 1. Beyond vesicle trafficking, BLOC1S2 interacts with HIPPI and sensitizes cells to apoptosis by enhancing caspase activation and mitochondrial membrane disruption 2. During hematopoietic development, BLOC1S2 maintains hematopoietic stem cell homeostasis by repressing Notch signaling 3. Clinically, BLOC1S2 mutations contribute to Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder characterized by defective LRO biogenesis, oculocutaneous albinism, platelet storage pool deficiency, and progressive pulmonary fibrosis 4. BLOC1S2 is downregulated in dendritic cells from COPD patients, suggesting potential involvement in chr10 obstructive pulmonary disease pathogenesis 5. Understanding BLOC1S2's molecular architecture and diverse cellular functions advances therapeutic strategies for lysosomal storage diseases and immune-mediated lung disorders.