Crystal structure of quinohemoprotein amine dehydrogenase from Pseudomonas putida: Identification of a novel quinone cofactor encaged by multiple thioether cross-bridges

Abstract The crystal structure of a quinohemoprotein amine dehydrogenase from Pseudomonas putida has been determined at 1.9-A resolution. The enzyme comprises three non-identical subunits: a four-domain α-subunit that harbors a di-heme cytochromec, a seven-bladed β-propeller β-subunit that provides part of the active site, and a small γ-subunit that contains a novel cross-linked, proteinous quinone cofactor, cysteine tryptophylquinone. More surprisingly, the catalytic γ-subunit contains three additional chemical cross-links that encage the cysteine tryptophylquinone cofactor, involving a cysteine side chain bridged to either an Asp or Glu residue all in a hitherto unknown thioether bonding with a methylene carbon atom of acidic amino acid side chains. Thus, the structure of the 79-residue γ-subunit is quite unusual, containing four internal cross-links in such a short polypeptide chain that would otherwise be difficult to fold into a globular structure.