Glutamate mutase and 2-methyleneglutarate mutase.

Abstract

Glutamate mutase converts ( S )-glutamate to ( S , S )-3-methylaspartate, whereas 2-methyleneglutarate mutase isomerizes 2-methyleneglutarate to ( R )-3-methylitaconate. Both enzymes occur in amino acid fermenting clostridia, require coenzyme B 12 (adenosylcobalamin) and catalyze a reversible, radical carbon skeleton rearrangement. The enzymes are assayed using the consecutive enzymes in their fermentation pathways: methylaspartase and methylitaconate isomerase, which produce the higher absorbing mesaconate and 2,3-dimethylmaleate, respectively. Although the quaternary structures of glutamate mutase and 2-methyleneglutarate mutase are different, the binding mode of coenzyme B 12 and their catalytic mechanism appear to be very similar. The crystal structure of glutamate mutase and EPR spectroscopy of both enzymes during catalysis revealed a distance of 6.6 Å between the C-H bond of the substrate to be cleaved and the Co-atom of cob(II)alamin. Methods are described for facile production of both enzymes in Escherichia coli and purification.