Plays a central role in the biogenesis of melanosomes. Involved in the maturation of melanosomes from stage I to II. The transition from stage I melanosomes to stage II melanosomes involves an elongation of the vesicle, and the appearance within of distinct fibrillar structures. Release of the soluble form, ME20-S, could protect tumor cells from antibody mediated immunity. Belongs to the PMEL/NMB family. 5 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.