Crystal structure and thermodynamic properties of D-lactate dehydrogenase from Lactobacillus jensenii

The thermostable D-lactate dehydrogenase from Lactobacillus jensenii (LjD-LDH) is a key enzyme in the production of the D-form of lactic acid from pyruvate concomitant with the oxidation of NADH to NAD+. The polymers of ID-lactic acid are used as biodegradable bioplastics. The crystal structures of LjD-LDH and in complex with NADI(+) were determined at 2.13 and 2.60 angstrom resolutions, respectively. The LjD-LDH monomer consists of the N-terminal substrate-binding domain and the C-terminal NAD-binding domain. The LjD-LDH forms a homodimeric structure, and the C-terminal NAD-binding domain mostly enables the dimerization of the enzyme. The NAD cofactor is bound to the GxGxxG NAD-binding motif located between the two domains. Structural comparisons of LjD-LDH with other D-LDHs reveal that LjD-LDH has unique amino acid residues at the linker region, which indicates that the open-close dynamics of LjD-LDH might be different from that of other D-LDHs. Moreover, thermostability experiments showed that the T-50(10) value of LjD-LDH (54.5 degrees C) was much higher than the commercially available D-lactate dehydrogenase (42.7 degrees C). In addition, LjD-LDH has at least a 7 degrees C higher denaturation temperature compared to commercially available D-LDHs. (C) 2014 Elsevier B.V. All rights reserved.