title: Proteolytic activation of human cathepsin A.
abstract: Galactosialidosis is a human lysosomal storage disease caused by deficiency in the multifunctional lysosomal protease cathepsin A (also known as protective protein/cathepsin A, PPCA, catA, HPP, and CTSA; EC 3.4.16.5). Previous structural work on the inactive precursor human cathepsin A (zymogen) led to a two-stage model for activation, where proteolysis of a 1.6-kDa excision peptide is followed by a conformational change in a blocking peptide occluding the active site. Here we present evidence for an alternate model of activation of human cathepsin A, needing only cleavage of a 3.3-kDa excision peptide to yield full enzymatic activity, with no conformational change required. We present x-ray crystallographic, mass spectrometric, amino acid sequencing, enzymatic, and cellular data to support the cleavage-only activation model. The results clarify a longstanding question about the mechanism of cathepsin A activation and point to new avenues for the design of mechanism-based inhibitors of the enzyme.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003; Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003.
authors.forename: Nilima
authors.initials: N
authors.lastname: Kolli
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003; Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003. Electronic address: garman@biochem.umass.edu.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Garman
mesh_terms: D043402:Cathepsin A / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation; D059748:Proteolysis
chemical_list: D043402:Cathepsin A
keywords: Glycoprotein Structure; Lysosomal Glycoproteins; Protease; Proteolytic Enzymes; X-ray Crystallography