Inactivation of Staphylococcus hyicus lipase by hexadecylsulfonyl fluoride: evidence for an active site serine |
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Authors: | Tjeenk Marjjke Leuveling; Bulsink Yvonne B M; Slotboom Arend J; Verheij Hubertus M; Haas Gerard Hde; Demleitner Gaby; Gotz Friedrich |
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Affiliation: | Department of Enzymology and Protein Engineering, Centre for Biomembranes and Lipid Enzymology, University of Utrecht The Netherlands
2Mikrobielle Genetilt, Universität Tbingen, Waldhuser Strasse 70/8, D-72076 Tbingen, Germany |
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Abstract: | The Staphylococcus hyicus lipase is an acyl hydrolase with broadsubstrate specificity including neutral glycerides and phospholipids.To obtain further insight into the mechanism of action of thisenzyme, we tested several sulfonyl fluorides as active site-directedinhibitors. The enzyme is resistant to the well-known serineprotease/esterase inhibitor phenylmethanesulfonyl fluoride (PMSF),but is rapidly inactivated by hexadecylsulfonyl fluoride. Thekinetics of inactivation were studied in Triton X-100 micelles.Inactivation is fast and the rate of inactivation is constantover the pH range where this lipase is active. Metal ions likeCa2+ and Sr2+ do not appreciably influence the rate of inactivation,although the enzymatic activity is significantly increased,suggesting a structural role for these ions. The S.hyicus lipasecontains a consensus sequence G-H/Y-S-X-G. Substitution by site-directedmutagenesis of this serine (Ser369) by a cysteine resulted ina mutant with only 0.2% residual activity. The activity of thismutant could not be inhibited with water-soluble sulfhydrylreagents either in the presence or absence of Triton X-100 micelles.In the presence of Triton X-100 micelles, inactivation of themutant occurred with 4-nitrophenylhexadecyl disulfide (t1/2= 125 min) while the wild-type enzyme does not react at all.We conclude that Ser369 is the active site residue and thatin water this residue is inaccessible. Only after interfacialactivation Ser369 (or Cys369) becomes exposed and reacts withirreversible inhibitors. |
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Keywords: | active site serine/ chemical modification/ lipolysis |
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