PROCESSING AND TRANSPORT OF A LYSOSOMAL MEMBRANE GLYCOPROTEIN IS DEVELOPMENTALLY-REGULATED IN AFRICAN TRYPANOSOMES

We have used pulse-chase immunoprecipitations methods to study early p ost-translational processing of CB1-gp, a lysosomal membrane glycoprot ein expressed by African trypanosomes. Rap67, a polyclonal antibody to CB1-gp, immunoprecipitated a 100-kDa glycoprotein, gp100, from both b loodstream forms (BF) and procyclic forms (PF) of Trypanosoma brucei g ambiense immediately after a 5-min pulse with radiomethionine. N-Glyca nase digestion released a 67-kDa core protein, p67, from gp100 of both life cycle forms. V8 protease digestion of p67 from BF and PF yielded 13 identical methionyl peptides, suggesting that gp100 from both life cycle forms have very similar or identical p67 core molecules, In BF, gp100 carried both endoglycosidase H (EndoH)-resistant and EndoH-sens itive, N-linked oligosaccharides immediately after labeling. In PF, al l the N-linked sugars on gp100 were EndoH sensitive. In BF, gp100 chas ed progressively into slower migrating 150-180-kDa components that obt ained the CBI epitope, traveled to the cell surface where they could b e biotinylated, and were proteolytically processed. The increase in ma ss of gp100 during chase in BF resulted from an elongation of N-linked oligosaccharides. Maturation of gp 100 into 150-180-kDa CB1-gp was in hibited if BF were chased in the presence of glucosidase inhibitors ca stanospermine or deoxynojirimycin. In PF, gp100 did not increase in ma ss, could not be biotinylated on the cell surface, and was not proetol yzed during extended chases. Cryoimmunoelectron microscopy revealed th at the antigens detected by rap67 are abundant in lysosomes and endoso mes in both BF and PF. Thus, BF and PF express very similar or identic al lysosomal membrane glycoproteins but process and transport them in very different ways.