Kinetic characterization and X-ray structure of a mutant of haloalkane dehalogenase with higher catalytic activity and modified substrate range.Schanstra, J.P., Ridder, I.S., Heimeriks, G.J., Rink, R., Poelarends, G.J., Kalk, K.H., Dijkstra, B.W., Janssen, D.B.
(1996) Biochemistry 35: 13186-13195
- PubMed: 8855957
- DOI: 10.1021/bi961151a
- PubMed Abstract:
- Refined X-Ray Structures of Haloalkane Dehalogenase at Ph 6.2 And Ph 8.2 And Implications for the Reaction Mechanism
Verschueren, K.H.,Franken, S.M.,Rozeboom, H.J.,Kalk, K.H.,Dijkstra, B.W.
(1993) J.Mol.Biol. 232: 856
- Crystal Structure of Haloalkane Dehalogenase: An Enzyme to Detoxify Halogenated Alkanes
Franken, S.M.,Rozeboom, H.J.,Kalk, K.H.,Dijkstra, B.W.
(1991) Embo J. 10: 1297
- Crystallization of Haloalkane Dehalogenase from Xanthobacter Autotrophicus Gj10
Rozeboom, H.J.,Kingma, J.,Janssen, D.B.,Dijkstra, B.W.
(1988) J.Mol.Biol. 200: 611
- Crystallographic Analysis of the Catalytic Mechanism of Haloalkane Dehalogenase
Verschueren, K.H.,Seljee, F.,Rozeboom, H.J.,Kalk, K.H.,Dijkstra, B.W.
(1993) Nature 363: 693
Conversion of halogenated aliphatics by haloalkane dehalogenase proceeds via the formation of a covalent alkyl-enzyme intermediate which is subsequently hydrolyzed by water. In the wild type enzyme, the slowest step for both 1,2-dichloroethane and 1, ...
Conversion of halogenated aliphatics by haloalkane dehalogenase proceeds via the formation of a covalent alkyl-enzyme intermediate which is subsequently hydrolyzed by water. In the wild type enzyme, the slowest step for both 1,2-dichloroethane and 1,2-dibromoethane conversion is a unimolecular enzyme isomerization preceding rapid halide dissociation. Phenylalanine 172 is located in a helix-loop-helix structure that covers the active site cavity of the enzyme, interacts with the C1 beta of 1,2-dichloroethane during catalysis, and could be involved in stabilization of this helix-loop-helix region of the cap domain of the enzyme. To obtain more information about the role of this residue in dehalogenase function, we performed a mutational analysis of position 172 and studied the kinetics and X-ray structure of the Phe172Trp enzyme. The Phe172Trp mutant had a 10-fold higher Kcat/Km for 1-chlorohexane and a 2-fold higher Kcat for 1,2-dibromoethane than the wild-type enzyme. The X-ray structure of the Phe172Trp enzyme showed a local conformational change in the helix-loop-helix region that covers the active site. This could explain the elevated activity for 1-chlorohexane of the Phe172Trp enzyme, since it allows this large substrate to bind more easily in the active site cavity. Pre-steady-state kinetic analysis showed that the increase in Kcat found for 1,2-dibromoethane conversion could be attributed to an increase in the rate of an enzyme isomerization step that preceeds halide release. The observed conformational difference between the helix-loop-helix structures of the wild-type enzyme and the faster mutant suggests that the isomerization required for halide release could be a conformational change that takes place in this region of the cap domain of the dehalogenase. It is proposed that Phe172 is involved in stabilization of the helix-loop-helix structure that covers the active site of the enzyme and creates a rigid hydrophobic cavity for small apolar halogenated alkanes.
Laboratory of Biochemistry, BIOSON Research Institute, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands.