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

The nonheme iron oxygenase VioC from Streptomyces vinaceus catalyzes Fe(II)-dependent and α-ketoglutarate-dependent Cβ-hydroxylation ofl-arginine during the biosynthesis of the tuberactinomycin antibiotic viomycin. Crystal structures of VioC were determined in complexes with the cofactor Fe(II), the substratel-arginine, the product (2 S,3 S)-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-hydroxylatedl-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 thel-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 analogsl-homoarginine andl-canavanine for Cβ-hydroxylation. [ABSTRACT FROM AUTHOR]