Haloalkane dehalogenase active site structure

Figure 12-1 The active site structure of haloalkane dehalogenase from Xanthobacter autotrophicus with a molecule of bound dichloroethane. See Pries et al.13 The arrows illustrate the initial nucleophilic displacement. The D260 - H289 pair is essential for the subsequent hydrolysis of the intermediate ester formed in the initial step.

Haloacid dehalogenase(s) 590 mechanism of 590 Haloalkane dehalogenase(s) 591 active site structure 591 Halocyanin 883 Haloperoxidases 855, 889 Hammerhead ribozyme 649, 651s mechanism of action 651 Hammett equation 308... 

Several membrane-bound and soluble epoxide hydrolases from mammalian origin have been purified and (at least partially) sequenced. Some of them have also been cloned and overexpressed, which is the case for the soluble EH from rat liver which has been overexpressed in Escherichia cob 54, 55. This enzyme (as well as its microsomal analog) was shown to share an amino acid sequence similarity to a region around the active center of a bacterial haloalkane dehalogenase 56, an enzyme with known three-dimensional structure that belongs to the a/(3-hydrolase fold-family 571. Rat soluble EH forms a dimer from two complete structural monomeric units, both possessing a distinct active site. The EH activity is known to be located close to the C-terminal unit, while the function of the N-terminal unit remains unknown 581. 

Previous studies on other bacterial hydrolytic dehalogenases have revealed different mechanisms and structures. High resolution X-ray structures of haloalkane dehalogenase(iO), 4-chlorobenzoyl CoA dehalogenase 31) and L-2-haloacid dehalogenase (52) revealed that these enzymes use an active site aspartate in nucleophilic displacement of the chlorine substituent as chloride anion. The enzyme-substrate ester intermediate is subsequently hydrolyzed by... 

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