PMID:11741915

Citation	Garcia-Alles, LF, Flükiger, K, Hewel, J, Gutknecht, R, Siebold, C, Schürch, S and Erni, B (2002) Mechanism-based inhibition of enzyme I of the Escherichia coli phosphotransferase system. Cysteine 502 is an essential residue. J. Biol. Chem. 277:6934-42
Abstract	Four phosphoenolpyruvate (PEP) derivatives, carrying reactive or activable chemical functions in each of the three chemical regions of PEP, were assayed as alternative substrates of enzyme I (EI) of the Escherichia coli PEP:glucose phosphotransferase system. The Z- and E-isomers of 3-chlorophosphoenolpyruvate (3-Cl-PEP) were substrates, presenting K(m) values of 0.08 and 0.12 mm, respectively, very similar to the K(m) of 0.14 mm measured for PEP, and k(cat) of 40 and 4 min(-1), compared with 2,200 min(-1), for PEP. The low catalytic efficiency of these substrates permits the study of activity at in vivo EI concentrations. Z-Cl-PEP was a competitive inhibitor of PEP with a K(I) of 0.4 mm. E-Cl-PEP was not an inhibitor. Compounds 3 and 4, obtained by modification of the carboxylic and phosphate groups of PEP, were neither substrates nor inhibitors of EI, highlighting the importance of these functionalities for recognition by EI. Z-Cl-PEP is a suicide inhibitor. About 10-50 turnovers sufficed to inactivate EI completely. Such a property can be exploited to reveal and quantitate phosphoryl transfer from EI to other proteins at in vivo concentrations. Inactivation was saturatable in Z-Cl-PEP, with an apparent K(m)(inact) of 0.2-0.4 mm. The rate of inactivation increased with the concentration of EI, indicating a preferential or exclusive reaction with the dimeric form of EI. E-Cl-PEP inactivates EI much more slowly, and unlike PEP, it did not protect against inactivation by Z-Cl-PEP. This and the ineffectiveness of E-Cl-PEP as a competitive inhibitor have been related to the presence of two EI active species. Cys-502 of EI was identified by mass spectrometry as the reacting residue. The C502A EI mutant showed less than 0.06% wild-type activity. Sequence alignments and comparisons of x-ray structures of different PEP-utilizing enzymes indicate that Cys-502 might serve as a proton donor during catalysis.
Links	PubMed Online version:10.1074/jbc.M110067200
Keywords	Amino Acid Sequence; Amino Acids/chemistry; Binding Sites; Binding, Competitive; Catalysis; Catalytic Domain; Cysteine/chemistry; Dimerization; Dose-Response Relationship, Drug; Enzyme Inhibitors/pharmacology; Escherichia coli/enzymology; Kinetics; Mass Spectrometry; Models, Chemical; Molecular Sequence Data; Mutagenesis, Site-Directed; Phosphoenolpyruvate Sugar Phosphotransferase System/antagonists & inhibitors; Phosphoenolpyruvate Sugar Phosphotransferase System/chemistry; Phosphorylation; Phosphotransferases/chemistry; Phosphotransferases/metabolism; Phosphotransferases (Nitrogenous Group Acceptor)/antagonists & inhibitors; Phosphotransferases (Nitrogenous Group Acceptor)/chemistry; Protein Binding; Protein Structure, Tertiary; Sequence Homology, Amino Acid; Spectrometry, Mass, Electrospray Ionization; Time Factors
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