Crystal structure of rice L-galactose dehydrogenase

L-Galactose dehydrogenase plays a key role in the biosynthesis of L-ascorbic acid (vitamin C) in plants. Here, we report crystal structures of rice (Oryza sativa) L-galactose dehydrogenase in both apo and NAD⁺-bound forms at 1.2 and 1.8 Å resolution, respectively. Rice L-galactose dehydrogenase adopts a conserved (β/α)₈-barrel fold with a well preserved NAD⁺-binding cleft, as in other plant L-galactose dehydrogenases. Structural comparisons revealed conformational flexibility in the first and second loop regions, which form the lid and side wall of the NAD⁺-binding site. These loops undergo significant rearrangement upon NAD⁺ binding, likely facilitating cofactor and substrate uptake. These findings suggest a flexible loop-mediated regulation of cofactor and substrate access.