Structural and enzymatic characterization of a purified prohormone-processing enzyme: secreted, soluble Kex2 protease.
The prohormone-processing Kex2 protease of the budding yeast Saccharomyces cerevisiae can be converted from an intracellular membrane protein to a soluble, secreted, and active form by deletion of the transmembrane domain and C-terminal tail. One such molecule was purified to near homogeneity from the culture medium of an overexpressing yeast strain. Amino acid sequence analysis revealed that the N terminus of mature Kex2 protease is created by a potentially autoproteolytic cleavage at Lys108-Arg109, prior to the domain homologous to subtilisin, followed by trimming of Leu-Pro and Val-Pro dipeptides by the Ste13 dipeptidyl aminopeptidase. Kinetic parameters were examined using fluorogenic peptidyl-methylcoumarin amide substrates. Initial burst titration indicated that the preparation was entirely active. Measurements of dependence of activity on pH yielded a simple curve suggesting titration of a single ionizable group. Activity was half-maximal at pH 5.7 and nearly constant from pH 6.5 to 9.5. Discrimination between substrates was as great as 360-fold in Km and 130-fold in kcat. Substrates with a Lys-Arg dipeptide preceding the cleaved bond were preferred, having kcat/Km values up to 1.1 x 10(7) sec-1.M-1. The enzyme cleaved substrates having Arg-Arg, Pro-Arg, Ala-Arg, and Thr-Arg with increased Km but with unchanged kcat. In contrast, the enzyme displayed a dramatically lower kcat for a Lys-Lys substrate with a smaller increase in Km. Thus the two residues preceding the cleaved bond may play distinct roles in the selectivity of binding and cleavage of prohormone substrates.
Brenner
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Department of Biochemistry, Stanford University School of Medicine, CA 94305.
Fuller
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D000595:Amino Acid Sequence; D001665:Binding Sites; D004252:DNA Mutational Analysis; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006023:Glycoproteins / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D043484:Proprotein Convertases; D011498:Protein Precursors / Q000378:metabolism*; D011994:Recombinant Proteins; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012995:Solubility; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013381:Subtilisins
D005656:Fungal Proteins; D006023:Glycoproteins; D010455:Peptides; D011498:Protein Precursors; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; D013381:Subtilisins; C058751:KEX2 protein, S cerevisiae