title: 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.
abstract: 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 HheA(AD2) from Arthrobacter sp. strain AD2 at 2.0-A resolution. Comparison with the previously reported structure of the 34% identical enantioselective haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1 shows that HheA(AD2) has a similar quaternary and tertiary structure but a much more open substrate-binding pocket. Docking experiments reveal that HheA(AD2) can bind both enantiomers of the haloalcohol substrate 1-p-nitrophenyl-2-chloroethanol in a productive way, which explains the low enantiopreference of HheA(AD2). 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 HheA(AD2), 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.
authors.affiliation: Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: René M
authors.initials: RM
authors.lastname: de Jong
authors.forename: Kor H
authors.initials: KH
authors.lastname: Kalk
authors.forename: Lixia
authors.initials: L
authors.lastname: Tang
authors.forename: Dick B
authors.initials: DB
authors.lastname: Janssen
authors.forename: Bauke W
authors.initials: BW
authors.lastname: Dijkstra
mesh_terms: D000595:Amino Acid Sequence; D001173:Arthrobacter / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D017124:Conserved Sequence; D006867:Hydrolases / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D013237:Stereoisomerism
chemical_list: D001426:Bacterial Proteins; D006867:Hydrolases; C113022:haloalcohol dehalogenase