Crystal structure of bacterial L-arabinose 1-dehydrogenase in complex with L-arabinose and NADP.

L-Arabinose 1-dehydrogenase (AraDH) is responsible for the first step of the non-phosphorylative L-arabinose pathway from bacteria, and catalyzes the NAD(P)-dependent oxidation of L-arabinose to L-arabinonolactone. This enzyme belongs to the so-called Gfo/Idh/MocA protein superfamily, but has a very poor phylogenetic relationship with other functional members. We previously reported the crystal structures of AraDH without a ligand and in complex with NADP. To clarify the underlying catalytic mechanisms in more detail, we herein elucidated the crystal structure in complex with L-arabinose and NADP. In addition to the previously reported five amino acid residues (Lys91, Glu147, His153, Asp169, and Asn173), His119, Trp152, and Trp231 interacted with L-arabinose, which were not found in substrate recognition by other Gfo/Idh/MocA members. Structure-based site-directed mutagenic analyses suggested that Asn173 plays an important role in catalysis, whereas Trp152, Trp231, and His119 contribute to substrate binding. The preference of NADP over NAD was significantly subjected by a pair of Ser37 and Arg38, whose manners were similar to other Gfo/Idh/MocA members.