LinA2, a HCH-converting bacterial enzyme that dehydrohalogenates HBCDs.
Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes (HCHs) are lipophilic, polyhalogenated hydrocarbons with comparable stereochemistry. Bacterial evolution in HCH-contaminated soils resulted in the development of several Spingomonadaceae which express a series of HCH-converting enzymes. We showed that LinB, a haloalkane dehalogenase from Sphingobium indicum B90A, also transforms various HBCDs besides HCHs. Here we present evidence that LinA2, another dehalogenase from S. indicum also converts certain HBCDs to pentabromocyclododecenes (PBCDEs). Racemic mixtures of α-, β-, γ-HBCDs, a mixture of them, and δ-HBCD, a meso form, were exposed to LinA2. Substantial conversion of (-)β-HBCD was observed, but all other stereoisomers were not transformed significantly. The enantiomeric excess (EE) of β-HBCDs increased up to 60% in 32 h, whereas EE values of α- and γ-HBCDs were not affected. Substrate conversion and product formation were described with second-order kinetic models. One major (P1β) and possibly two minor (P2β, P3β) metabolites were detected. Respective mass spectra showed the characteristic isotope pattern of PBCDEs, the HBr elimination products of HBCDs. Michaelis-Menten parameters KM=0.47 ± 0.07 μM and vmax=0.17 ± 0.01 μmoll(-1)h(-1) were deduced from exposure data with varying enzyme/substrate ratios. LinA2 is more substrate specific than LinB, the latter converted all tested HBCDs, LinA2 only one. The widespread HCH pollution favored the selection and evolution of bacteria converting these compounds. We found that LinA2 and LinB, two of these HCH-converting enzymes expressed in S. indicum B90A, also dehalogenate HBCDs to lower brominated compounds, indicating that structural similarities of both classes of compounds are recognized at the level of substrate-protein interactions.
Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Analytical Chemistry, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland. Electronic address: norbert.heeb@empa.ch.
Norbert V
NV
Heeb
Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Analytical Chemistry, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland; ZHAW, Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Reidbach, CH-8820 Wädenswil, Switzerland.
Simon A
SA
Wyss
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Birgit
B
Geueke
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Thomas
T
Fleischmann
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Hans-Peter E
HE
Kohler
ZHAW, Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, Reidbach, CH-8820 Wädenswil, Switzerland.
Peter
P
Lienemann
D055162:Biocatalysis; D001711:Biotransformation; D054879:Halogenation; D001556:Hexachlorocyclohexane / Q000378:metabolism*; D006842:Hydrocarbons, Brominated / Q000737:chemistry / Q000378:metabolism*; D006867:Hydrolases / Q000378:metabolism*; D007700:Kinetics; D011137:Polystyrenes / Q000737:chemistry; D012989:Soil Pollutants / Q000378:metabolism*; D042301:Sphingomonadaceae / Q000201:enzymology / Q000378:metabolism*; D013237:Stereoisomerism
D006842:Hydrocarbons, Brominated; D011137:Polystyrenes; D012989:Soil Pollutants; D001556:Hexachlorocyclohexane; C089796:hexabromocyclododecane; D006867:Hydrolases; C046137:haloalkane dehalogenase
Brominated flame retardants; HBCD biotransformation; HCH-converting bacterial enzyme; LinA2 metabolites; Persistent organic pollutants