Lysosome-related organelles

Lysosomes are membrane-bound cytoplasmic organelles involved in intracellul ar protein degradation, They contain an assortment of soluble acid-dependen t hydrolases and a set of highly glycosylated integral membrane proteins, M ost of the properties of lysosomes are shared with a group of cell type-spe cific compartments referred to as 'lysosome-related organelles', which incl ude melanosomes, lytic granules, MHC class II compartments, platelet-dense granules, basophil granules, azurophil granules, and Drosophila pigment gra nules. In addition to lysosomal proteins, these organelles contain cell typ e-specific components that are responsible for their specialized functions. Abnormalities in both lysosomes and lysosome-related organelles have been observed in human genetic diseases such as the Chediak-Higashi and Hermansk y-Pudlak syndromes, further demonstrating the close relationship between th ese organelles. Identification of genes mutated in these human diseases, as well as in mouse and Drosophila pigmentation mutants, is beginning to shed light on the molecular machinery involved in the biogenesis of lysosomes a nd lysosome-related organelles.