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

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-Å 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.