Crystallization of the catalytic subunit of Saccharomyces cerevisiae acetohydroxyacid synthase.

Acetohydroxyacid synthase (AHAS; E.C. 4.1.3.18) is the first enzyme in the biosynthetic pathway of the branched-chain amino acids isoleucine, leucine and valine. It is a thiamin diphosphate-dependent enzyme which catalyses the decarboxylation of pyruvate and its condensation with either 2-ketobutyrate or a second molecule of pyruvate to give 2-aceto-2-hydroxybutyrate or 2-acetolactate, respectively. The enzyme is the target of sulfonylurea and imidazolinone herbicides, which act as potent and specific inhibitors. Here, the crystallization and preliminary X-ray diffraction analysis of the catalytic subunit of Saccharomyces cerevisiae AHAS is reported. Data to 2.7 A resolution have been collected using synchrotron radiation (Advanced Photon Source, Chicago). Crystals have unit-cell parameters a = 95.8, b = 110.0, c = 178.9 A and belong to the space group P2(1)2(1)2(1). Preliminary analysis indicates there is one dimer located in each asymmetric unit.