Structural highlights
Publication Abstract from PubMedMandelate racemase (MR), a member of the enolase superfamily, catalyzes the Mg(2+)-dependent interconversion of the enantiomers of mandelate. Several alpha-keto acids are modest competitive inhibitors of MR [e.g., mesoxalate (Ki = 1.8 +/- 0.3 mM) and 3-fluoropyruvate (Ki = 1.3 +/- 0.1 mM)], but, surprisingly, 3-hydroxypyruvate (3-HP) is an irreversible, time-dependent inhibitor (kinact/KI = 83 +/- 8 M(-1) s(-1)). Protection from inactivation by the competitive inhibitor benzohydroxamate, trypsinolysis and electrospray ionization tandem mass spectrometry analyses, and X-ray crystallographic studies reveal that 3-HP undergoes Schiff-base formation with Lys 166 at the active site, followed by formation of an aldehyde/enol(ate) adduct. Such a reaction is unprecedented in the enolase superfamily and may be a relic of an activity possessed by a promiscuous progenitor enzyme. The ability of MR to form and deprotonate a Schiff-base intermediate furnishes a previously unrecognized mechanistic link to other alpha/beta-barrel enzymes utilizing Schiff-base chemistry and is in accord with the sequence- and structure-based hypothesis that members of the metal-dependent enolase superfamily and the Schiff-base-forming N-acetylneuraminate lyase superfamily and aldolases share a common ancestor. Inactivation of Mandelate Racemase by 3-Hydroxypyruvate Reveals a Potential Mechanistic Link between Enzyme Superfamilies.,Nagar M, Wyatt BN, St Maurice M, Bearne SL Biochemistry. 2015 May 5;54(17):2747-57. doi: 10.1021/acs.biochem.5b00221. Epub, 2015 Apr 20. PMID:25844917[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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