calicheamicin-gamma(1)i and alpha-ketobutyric-acid

CalE6 is a previously uncharacterized protein involved in the biosynthesis of calicheamicins in Micromonospora echinospora. It is a pyridoxal-5'-phosphate-dependent enzyme and exhibits high sequence homology to cystathionine γ-lyases and cystathionine γ-synthases. However, it was found to be active towards methionine and to convert this amino acid into α-ketobutyrate, ammonium, and methanethiol. The crystal structure of the cofactor-bound holoenzyme was resolved at 2.0 Å; it contains two active site residues, Gly105 and Val322, specific for methionine γ-lyases. Modeling of methionine into the active site allows identification of the active site residues responsible for substrate recognition and catalysis. These findings support that CalE6 is a putative methionine γ-lyase producing methanethiol as a building block in biosynthesis of calicheamicins.

Topics: Amino Acid Sequence; Aminoglycosides; Ammonium Compounds; Bacterial Proteins; Butyrates; Carbon-Oxygen Lyases; Carbon-Sulfur Lyases; Catalytic Domain; Coenzymes; Crystallography, X-Ray; Enediynes; Gene Expression; Holoenzymes; Methionine; Micromonospora; Models, Molecular; Molecular Sequence Data; Multigene Family; Pyridoxal Phosphate; Sequence Alignment; Sequence Homology, Amino Acid; Sulfhydryl Compounds