Faculty Collaboration Database

A Paradigm for CH Bond Cleavage: Structural and Functional Aspects of Transition State Stabilization by Mandelate Racemase. Adv Protein Chem Struct Biol 2017;109:113-160

Date

07/08/2017

Pubmed ID

28683916

DOI

10.1016/bs.apcsb.2017.04.007

Scopus ID

2-s2.0-85020471994 (requires institutional sign-in at Scopus site)   15 Citations

Abstract

Mandelate racemase (MR) from Pseudomonas putida catalyzes the Mg²⁺-dependent, 1,1-proton transfer reaction that racemizes (R)- and (S)-mandelate. MR shares a partial reaction (i.e., the metal ion-assisted, Brønsted base-catalyzed proton abstraction of the α-proton of carboxylic acid substrates) and structural features ((β/α)₇β-barrel and N-terminal α + β capping domains) with a vast group of homologous, yet functionally diverse, enzymes in the enolase superfamily. Mechanistic and structural studies have developed this enzyme into a paradigm for understanding how enzymes such as those of the enolase superfamily overcome kinetic and thermodynamic barriers to catalyze the abstraction of an α-proton from a carbon acid substrate with a relatively high pK_a value. Structural studies on MR bound to intermediate/transition state analogues have delineated those structural features that MR uses to stabilize transition states and enhance reaction rates of proton abstraction. Kinetic, site-directed mutagenesis, and structural studies have also revealed that the phenyl ring of the substrate migrates through the hydrophobic cavity within the active site during catalysis and that the Brønsted acid-base catalysts (Lys 166 and His 297) may be utilized as binding determinants for inhibitor recognition. In addition, structural studies on the adduct formed from the irreversible inhibition of MR by 3-hydroxypyruvate revealed that MR can form and deprotonate a Schiff-base with 3-hydroxypyruvate to yield an enol(ate)-aldehyde adduct, suggesting a possible evolutionary link between MR and the Schiff-base forming aldolases. As the archetype of the enolase superfamily, mechanistic and structural studies on MR will continue to enhance our understanding of enzyme catalysis and furnish insights into the evolution of enzyme function.

Author List

Bearne SL, St Maurice M

Author

Martin St. Maurice PhD Associate Professor in the Biology department at Marquette University

MESH terms used to index this publication - Major topics in bold

Bacteria
Catalytic Domain
Kinetics
Mandelic Acids
Models, Molecular
Pseudomonas putida
Racemases and Epimerases
Substrate Specificity
Thermodynamics