3-DIMENSIONAL STRUCTURE OF L-2-HALOACID DEHALOGENASE FROM XANTHOBACTER-AUTOTROPHICUS GJ10 COMPLEXED WITH THE SUBSTRATE-ANALOG FORMATE

The L-2-haloacid dehalogenase from the 1,2-dichloroethane degrading ba cterium Xanthobacter autotrophicus GJ10 catalyzes the hydrolytic dehal ogenation of small L-2-haloalkanoic acids to yield the corresponding D -2-hydroxyalkanoic acids. Its crystal structure was solved by the meth od of multiple isomorphous replacement with incorporation of anomalous scattering information and solvent flattening, and was refined at 1.9 5-Angstrom resolution to an R factor of 21.3%. The three-dimensional s tructure is similar to that of the homologous L-2-haloacid dehalogenas e from Pseudomonas sp, YL (1), but the X. autotrophicus enzyme has an extra dimerization domain, an active site cavity that is completely sh ielded from the solvent, and a different orientation of several cataly tically important amino acid residues, Moreover, under the conditions used, a formate ion is bound in the active site, The position of this substrate-analogue provides valuable information on the reaction mecha nism and explains the limited substrate specificity of the Xanthobacte r L-2-haloacid dehalogenase.