X-RAY STRUCTURE OF A REACTION INTERMEDIATE OF L-2-HALOACID DEHALOGENASE WITH L-2-CHLOROPROPIONAMIDE

The crystal structure of a complex prepared by soaking a single crysta l of the S175A mutant of L-2-haloacid dehalogenase from Pseudomonas sp , YL in a solution containing a poor substrate, L-2-chloropropionamide , has been determined by X-ray analysis at 2.15 Angstrom resolution wi th a crystallographic R factor of 19.80%. The present analysis has rev ealed the structure of the reaction intermediate trapped in the crysta l. In the intermediate, the substrate moiety lacking chlorine is coval ently bound to the carboxyl group of D10, and adopts the pro-D-configu ration at the C-2 atom, The amide group of the substrate is hydrogen-b onded with the hydroxy group of S118, The methyl group bound to the C- 2 atom exists in a hydrophobic pocket which is important for recogniti on of the alkyl group of the substrate, The guanidino group of R41 has reasonable orientation for halogen-abstraction.