Biosynthesis of a lysosomal enzyme. Partial structure of two transient and functionally distinct NH2-terminal sequences in cathepsin D

摘要: Various biosynthetic forms of porcine spleen cathepsin D (Erickson, A. H. and Blobel, G. (1979) J. Biol. Chem. 254, 11771-11774), isolated by immunoprecipitation in vivo- vitro-synthesized products, have been characterized partial NH2-terminal sequence analysis. Two short lived functionally distinct extensions, a "pre" "pro" sequence, detected. Both extensions are present preprocathepsin which is the primary translation product immunoprecipitated after mRNA wheat germ cell-free system. Preprocathepsin not glycosylated has an approximate Mr = 43,000. Its 20-residue pre resembles signal sequences presecretory proteins abundance Leu residues (7 out 20 residues). Addition dog pancreatic microsomal vesicles to system resulted cleavage yielded segregated procathepsin (Mr 46,000) that was indistinguishable from its vivo-synthesized counterpart detected pulse-labeling cultured kidney cells. Some this secreted persisted as such culture medium. The remainder converted within period 15 min 2 h single chain 44,000) removal pro estimated be 44 residues. showed considerable homology 44-residue activation peptide pepsinogen. It possible, therefore, prosequence serves keeps enzyme inactive during intracellular transport lysosome. enzymatically active form undergoes further into light heavy 15,000 30,000, respectively) over 2-24 synthesis. oligosaccharide moieties cleaved endoglycosidase Treatment cells with tunicamycin arrests pathway at D. nonglycosylated proteolytically processed secretion greatly inhibited.