Role of esterase gp70 and its influence on growth and development of Dictyostelium discoideum

Gp70 is an esterase originally called crystal protein because of its presen ce in crystalline structures in aggregation-competent Dictyostelium discoid eum cells. Although postulated to break down spore coats, the function of g p70 in vivo was incompletely investigated. Our immunolocalization and bioch emical studies of vegetative D. discoideum amoebae show that gp70 was recru ited to phagosomes and found in lysosomes. Purified gp70. was effective at hydrolyzing naphthyl substrates with acyl chains typical of lipids and lipo polysaccharides, indicating that the gp70 was involved in digesting endocyt osed molecules. The activity of purified gp70 was inhibited by reductants t hat retarded its electrophoretic mobility and verified the presence of intr amolecular disulfide bonds predicted by its amino acid sequence. Compared t o wild-type cells, cells overexpresing gp70 were more phagocytically active , had shorter generation times, and produced more fruiting bodies per unit area, while cells lacking gp70 were phagocytically less active with longer doubling times, developed more slowly, and had significantly fewer fruiting bodies per unit area. Consistent with the phenotype of a disrupted metabol ism, one-third of the gp70-minus cells were large and multinucleated. Toget her, these results indicated that despite its crystalline appearance, gp70 was an active esterase involved in both the growth and the development of D . discoideum. (C) 2000 Academic Press.