Site-directed Mutagenesis of Two Zinc-binding Centers of the NADH-dependent Phenylacetaldehyde Reductase from Styrene-assimilatingCorynebacteriumsp. Strain ST-10

Phenylacetaldehyde reductase (PAR) with a unique and wide substrate range from styrene-assimilating Corynebacterium sp. strain ST-10, which is a useful biocatalyst producing chiral alcohols, has been found to belong to a family of zinc-containing, long-chain alcohol dehydrogenases (ADHs) on the basis of the primary structure similarity. The enzyme contains 2 moles of zinc per mole of subunit. The amino acid residues assumed to be three catalytic and four structural zinc-binding ligands were characterized by site-directed mutagenesis, compared with other zinc-containing, long-chain ADHs. Sixteen PAR mutants gave measurable but rather low activities toward phenylacetaldehyde, n-hexyl aldehyde, and 2-heptanone, although they maintained the activities of 8 to 16% of that of wild-type PAR for an acetophenone substrate except that the D153N mutant showed quite low activity. The results suggested that the seven residues present in PAR were probably zinc-binding ligands, and mutation in these residues caused a change in activities for some substrates.