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 crystal 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 A resolution with a crystallographic R factor of 19.8%. The present analysis has revealed the structure of the reaction intermediate trapped in the crystal. In the intermediate, the substrate moiety lacking chlorine is covalently bound to the carboxyl group of D10, and adopts the pro-D-configuration at the C2 atom. The amide group of the substrate is hydrogen-bonded with the hydroxy group of S118. The methyl group bound to the C2 atom exists in a hydrophobic pocket which is important for recognition of the alkyl group of the substrate. The guanidino group of R41 has reasonable orientation for halogen-abstraction.