Title

Inactivation of Mandelate Racemase by 3-Hydroxypyruvate Reveals a Potential Mechanistic Link between Enzyme Superfamilies

Document Type

Article

Language

eng

Format of Original

11 p.

Publication Date

5-5-2015

Publisher

American Chemical Society

Source Publication

Biochemistry

Source ISSN

0006-2960

Original Item ID

DOI: 10.1021/acs.biochem.5b00221, PubMed Central: PMID: 25844917

Abstract

Mandelate racemase (MR), a member of the enolase superfamily, catalyzes the Mg2+-dependent interconversion of the enantiomers of mandelate. Several α-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 α/β-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.

Comments

Biochemistry, Vol. 54, No. 17 (May 5, 2015): 2747-2757. DOI.