Structural basis for the erythro-stereospecificity of the l-arginine oxygenase VioC in viomycin biosynthesis

Abstract

The nonheme iron oxygenase VioC from Streptomyces vinaceus catalyzes Fe(II)-dependent and α-ketoglutarate-dependent Cβ-hydroxylation of l-arginine during the biosynthesis of the tuberactinomycin antibiotic viomycin. Crystal structures of VioC were determined in complexes with the cofactor Fe(II), the substrate l-arginine, the product (2S,3S)-hydroxyarginine and the coproduct succinate at 1.1-1.3 Å resolution. The overall structure reveals a β-helix core fold with two additional helical subdomains that are common to nonheme iron oxygenases of the clavaminic acid synthase-like superfamily. In contrast to other clavaminic acid synthase-like oxygenases, which catalyze the formation of threo diastereomers, VioC produces the erythro diastereomer of Cβ-hydroxylated l-arginine. This unexpected stereospecificity is caused by conformational control of the bound substrate, which enforces a gauche(-) conformer for χ1 instead of the trans conformers observed for the asparagine oxygenase AsnO and other members of the clavaminic acid synthase-like superfamily. Additionally, the substrate specificity of VioC was investigated. The side chain of the l-arginine substrate projects outwards from the active site by undergoing interactions mainly with the C-terminal helical subdomain. Accordingly, VioC exerts broadened substrate specificity by accepting the analogs l-homoarginine and l-canavanine for Cβ-hydroxylation. © 2009 FEBS.