The role of amino acid residues in the enzymatic activity of carboxylesterase from Arthrobacter globiformis was analyzed by diisopropyl fluorophosphate (DFP) labeling and site-directed mutagenesis. The electrospray ionization mass spectrometric (ESI-MS) analysis of the esterase, covalently labeled by DFP, showed stoichiometric incorporation of the inhibitor into the enzyme. The further comparison of endopeptidase-digested fragments between native and DFP-labeled esterase by fast atom bombardment mass spectrometric (FAB-MS) analysis as well as site-directed mutagenesis indicated that Ser59 in the consensus sequence Ser-X-X-Lys, which is conserved exclusively in penicillin-binding proteins and some esterases, served as a catalytic nucleophile. In addition, the results obtained from analysis of the mutants at position 62 suggested the importance of the basic amino acid side chain at this position, and suggested the significance of this residue acting directly as a general base rather than its involvement in the maintenance of the optimum hydrogen-bonding network at the active site.
通过
二异丙基氟磷酸盐(DFP)标记和定点突变分析了来自球形放线菌(Arthrobacter globiformis)
羧酸酯酶中
氨基酸残基在酶活性中的作用。对共价标记的
酯酶进行电喷雾电离质谱(ESI-MS)分析显示,
抑制剂以计量关系结合到酶中。通过快速原子撞击质谱(FAB-MS)分析,进一步比较了野生型与DFP标记
酯酶之间的内肽酶消化片段,结合定点突变结果表明,保守序列Ser-X-X-Lys中的Ser59,专门存在于
青霉素结合蛋白和某些
酯酶中,充当了催化核苷酸。此外,对62位突变体的分析结果表明,该位置的碱性
氨基酸侧链的重要性,并建议这一残基直接作为一般碱的作用比其参与维持活性位点的最佳氢键网络更为重要。