Specificity of yeast KEX2 protease for variant human proalbumins is identical to the in vivo specificity of the hepatic proalbumin convertase.
Yeast KEX2 protease was examined as a potential model for a human proprotein convertase and, in all respects, mimicked the predicted properties of a proalbumin convertase. The enzyme rapidly cleaved the propeptide Arg-Gly-Val-Phe-Arg-Arg from the NH2-terminal end of proalbumin but, unlike trypsin, failed to cleave physiologically unprocessed human proalbumin variants. There was little or no cleavage of proalbumin Lille (Arg-2----His) or Christchurch (Arg-1----Gln), and there was negligible cleavage of proalbumin Blenheim (Asp1----Val), despite the fact that it retains the dibasic processing signal. Proalbumin Kaikoura (Arg-2----Cys), which appears to be partially processed in vivo, was cleaved at about half the rate of normal proalbumin despite the absence of a diarginyl sequence. Restoration of a dibasic site through aminoethylation of the new cysteine increased the rate of cleavage to near that of normal proalbumin. The KEX2-catalyzed cleavage of normal proalbumin was found to be independent of pH between pH 6.0 and 8.0. Antitrypsin Pittsburgh (Met358----Arg), a predicted specific inhibitor of in vivo proalbumin cleavage, inhibited KEX2 in a reversible manner. A molar excess of thrombin over antitrypsin Pittsburgh relieved the inhibition of KEX2, suggesting that a covalent complex is not formed between KEX2 and the inhibitor.
Brennan
S O
SO
Department of Clinical Biochemistry, Christchurch Hospital, New Zealand.
Peach
R J
RJ
Bathurst
I C
IC
D000595:Amino Acid Sequence; D010450:Endopeptidases / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009154:Mutation; D011228:Prealbumin / Q000235:genetics / Q000378:metabolism*; D043484:Proprotein Convertases; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D012697:Serine Endopeptidases / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013381:Subtilisins; D000515:alpha 1-Antitrypsin / Q000235:genetics / Q000378:metabolism*
D011228:Prealbumin; D029701:Saccharomyces cerevisiae Proteins; D000515:alpha 1-Antitrypsin; D010450:Endopeptidases; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; D013381:Subtilisins; C058751:KEX2 protein, S cerevisiae; C060483:proalbumin convertase, mammalian