Structural and mutational characterization of a malate racemase from the LarA superfamily

Irreversible Inactivation of Lactate Racemase by Sodium Borohydride Reveals Reactivity of the Nickel–Pincer Nucleotide Cofactor

“…Since the discovery of the NPN cofactor in 2015, the large LarA superfamily, previously denoted as the DUF2088 family, was shown to consist of highly diverse family members catalyzing racemization/epimerization reactions on a variety of α-hydroxyacids with many representatives catalyzing unknown reactions. 11,12 The reaction mechanism of LarA Lp , the founding member of the LarA superfamily, has been extensively studied. 13 A protoncoupled hydride-transfer (PCHT) mechanism (Scheme 1b), where the left and right half-reactions of LarA Lp are analogous to the entire reactions of L-and D-lactate dehydrogenases, 1 has been proposed based on the enzyme structure, a substrate kinetic isotope effect, identification of the pyruvate intermediate, spectroscopic changes with an added substrate, and computational investigations.…”

“…LarA from Lactiplantibacillus plantarum (LarA Lp ) is a lactate racemase that interconverts the l - and d -enantiomers of the α-hydroxyacid. , As the ninth nickel-dependent enzyme discovered in nature, LarA Lp utilizes a novel nickel–pincer nucleotide (NPN) cofactor (Scheme a) to catalyze the isomerization reaction. , The coenzyme is synthesized from nicotinic acid adenine dinucleotide by consecutive actions of the LarB carboxylase/hydrolase, LarE sulfur transferase, , and LarC nickel insertase. , The most prominent characteristic of the NPN cofactor is the direct bonding between Ni 2+ and the C4 atom in its pyridinium ring, representing the first C–Ni bond (other than transient intermediates) identified in a biological system. Since the discovery of the NPN cofactor in 2015, the large LarA superfamily, previously denoted as the DUF2088 family, was shown to consist of highly diverse family members catalyzing racemization/epimerization reactions on a variety of α-hydroxyacids with many representatives catalyzing unknown reactions. , …”

Irreversible inactivation of lactate racemase by sodium borohydride reveals reactivity of the nickel-pincer nucleotide cofactor

“…Since the discovery of the NPN cofactor in 2015, the large LarA superfamily, previously denoted as the DUF2088 family, was shown to consist of highly diverse family members catalyzing racemization/epimerization reactions on a variety of α-hydroxyacids with many representatives catalyzing unknown reactions. 8 The reaction mechanism of LarALp, the founding member of the LarA superfamily, has been extensively studied. 9 A proton-coupled hydride-transfer (PCHT) mechanism (Scheme 1B), where each half reaction is utilized in D-/L-lactate dehydrogenases, 1 has been proposed based on the enzyme structure, a substrate kinetic isotope effect, identification of the pyruvate intermediate, spectroscopic changes with added substrate, and computational investigations.…”