Structural insights into the catalytic and substrate recognition mechanisms of bacterial l -arabinose 1-dehydrogenase

[摘要] In Azospirillum brasilense, a gram-negative nitrogen-fixing bacterium, L-arabinose is converted to a-ketoglutarate through a nonphosphorylative metabolic pathway. In the first step in the pathway, L-arabinose is oxidized to L-arabino-c-lactone by NAD(P)-dependent L-arabinose 1-dehydrogenase (AraDH) belonging to the glucose-fructose oxidoreductase/inositol dehydrogenase/rhizopine catabolism protein (Gfo/Idh/MocA) family. Here, we determined the crystal structures of apo- and NADP-bound AraDH at 1.5 and 2.2 A resolutions, respectively. A docking model of L-arabinose and NADPbound AraDH and structure-based mutational analyses suggest that Lys91 or Asp169 serves as a catalytic base and that Glu147, His153, and Asn173 are responsible for substrate recognition. In particular, Asn173 may play a role in the discrimination between L-arabinose and D-xylose, the C4 epimer of L-arabinose.

[关键词] crystal structure;L-arabinose 1-dehydrogenase;L-arabinose metabolism