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Haloalkane dehalogenases: structure of a Rhodococcus enzyme
J Newman1, T S Peat, R Richard
1Life Sciences Division, Los Alamos National Laboratory, New Mexico. janet@stromix.com
Biochemistry
|December 10, 1999
Summary
Haloalkane dehalogenases from Rhodococcus and Xanthobacter show distinct structural and catalytic properties. The Rhodococcus enzyme
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Haloalkane dehalogenases are crucial for bioremediation and biocatalysis.
- Two main classes exist: Xanthobacter and Rhodococcus enzymes, sharing 30% sequence identity but differing in substrate specificity and halide binding.
- Understanding their structural basis is key to optimizing their applications.
Purpose of the Study:
- To elucidate the structural basis for the differing substrate specificities and halide-binding properties of Rhodococcus and Xanthobacter haloalkane dehalogenases.
- To determine the crystal structure of the Rhodococcus dehalogenase and compare it with the Xanthobacter enzyme.
Main Methods:
- X-ray crystallography was used to determine the 1.5 Å resolution crystal structure of the Rhodococcus dehalogenase.
- Structures were obtained at pH 5.5, pH 7.0, and in the presence of NaI.
- Comparative structural analysis with the Xanthobacter enzyme was performed.
Main Results:
- The Rhodococcus and Xanthobacter enzymes share structural homology in their core but differ in the cap domain, with Rhodococcus having a larger active site cavity.
- A distinct catalytic triad topology was observed: Rhodococcus utilizes E141, while Xanthobacter uses D260.
- Two iodide binding sites were identified in the Rhodococcus enzyme, and a rare stable S-I covalent bond was observed with C187 when cocrystallized with NaI.
Conclusions:
- The structural differences, particularly in the cap domain and active site cavity, explain the broader substrate specificity of the Rhodococcus dehalogenase.
- The distinct catalytic triad and halide-binding mechanisms highlight the evolutionary divergence between the two enzyme classes.
- These findings provide insights for engineering dehalogenases with tailored biocatalytic functions.
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