InterPro domain: IPR039557

This entry represents the N-terminal ACT domain of the Escherichia coli IlvH-like regulatory subunit of acetolactate synthase (acetohydroxyacid synthase; AHAS). AHAS catalyses the first common step in the biosynthesis of the three branched-chain amino acids (leucine, isoleucine, and valine). The first step involves the condensation of either pyruvate or 2-ketobutyrate with the two-carbon hydroxyethyl fragment derived from another pyruvate molecule, covalently bound to the coenzyme thiamine diphosphate. Bacterial AHASs generally consist of regulatory and catalytic subunits. The effector (valine) binding sites are proposed to be located in two symmetrically related positions in the interface between a pair of N-terminal ACT domains with the C-terminal domain of IlvH contacting the catalytic dimer. Plants Arabidopsis and Oryza have tandem IlvH subunits; both the first and second ACT domain sequences are present in this entry [ 1 ].

1. Structure of the regulatory subunit of acetohydroxyacid synthase isozyme III from Escherichia coli. J. Mol. Biol. 357, 951-63