Processing of surfactant protein B proprotein by a cathepsin D-like protease.

摘要: Surfactant protein B (SP-B) is a hydrophobic peptide of relative molecular weight (M(r)) = 8,000 that associated with pulmonary surfactant phospholipids. SP-B synthesized by the alveolar type II epithelial cell as proprotein M(r) 42,000 which requires at least two proteolytic cleavages to generate 79 residue mature peptide. We have previously reported cleavage NH2-terminal propeptide, processing intermediate 25,000, occurs in close temporal approximation secretion. In present study we demonstrate proprotein, isolated from stably transfected Chinese hamster ovary cells, processed 25,000 crude membrane fraction but not intact cells or conditioned media. vitro preparation resulted release single 16,000–17,000, was detected antiserum directed against antigenic epitopes propeptide precursor. activity extracted Na2CO3 lysis preparation, had pH optimum 5.0–6.0, and inhibited 10(-7) M pepstatin A, suggesting precursor cleaved an aspartyl protease. Consistent this hypothesis, blocked protease cathepsin D; further, purified D efficiently 25,000. Collectively these results suggest mediated D-like localized within secretory pathway cell.