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Journal of Bacteriology, June 2006, p. 4051-4056, Vol. 188, No. 11
0021-9193/06/$08.00+0     doi:10.1128/JB.01866-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The X-Ray Structure of the Haloalcohol Dehalogenase HheA from Arthrobacter sp. Strain AD2: Insight into Enantioselectivity and Halide Binding in the Haloalcohol Dehalogenase Family

René M. de Jong,1,{dagger} Kor H. Kalk,1 Lixia Tang,2 Dick B. Janssen,2 and Bauke W. Dijkstra1*

Laboratory of Biophysical Chemistry,1 Laboratory of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands2

Received 7 December 2005/ Accepted 17 March 2006

Haloalcohol dehalogenases are bacterial enzymes that cleave the carbon-halogen bond in short aliphatic vicinal haloalcohols, like 1-chloro-2,3-propanediol, some of which are recalcitrant environmental pollutants. They use a conserved Ser-Tyr-Arg catalytic triad to deprotonate the haloalcohol oxygen, which attacks the halogen-bearing carbon atom, producing an epoxide and a halide ion. Here, we present the X-ray structure of the haloalcohol dehalogenase HheAAD2 from Arthrobacter sp. strain AD2 at 2.0-Å resolution. Comparison with the previously reported structure of the 34% identical enantioselective haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1 shows that HheAAD2 has a similar quaternary and tertiary structure but a much more open substrate-binding pocket. Docking experiments reveal that HheAAD2 can bind both enantiomers of the haloalcohol substrate 1-p-nitrophenyl-2-chloroethanol in a productive way, which explains the low enantiopreference of HheAAD2. Other differences are found in the halide-binding site, where the side chain amino group of Asn182 is in a position to stabilize the halogen atom or halide ion in HheAAD2, in contrast to HheC, where a water molecule has taken over this role. These results broaden the insight into the structural determinants that govern reactivity and selectivity in the haloalcohol dehalogenase family.

* Corresponding author. Mailing address: Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. Phone: 31-50-3634381. Fax: 31-50-3634800. E-mail: B.W.Dijkstra{at}rug.nl.

{dagger} Present address: Department of Chemistry, Columbia University, 3000 Broadway MC3153, New York, NY 10027.

Journal of Bacteriology, June 2006, p. 4051-4056, Vol. 188, No. 11
0021-9193/06/$08.00+0     doi:10.1128/JB.01866-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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