title: Biochemistry of microbial degradation of hexachlorocyclohexane and prospects for bioremediation.
abstract: Lindane, the gamma-isomer of hexachlorocyclohexane (HCH), is a potent insecticide. Purified lindane or unpurified mixtures of this and alpha-, beta-, and delta-isomers of HCH were widely used as commercial insecticides in the last half of the 20th century. Large dumps of unused HCH isomers now constitute a major hazard because of their long residence times in soil and high nontarget toxicities. The major pathway for the aerobic degradation of HCH isomers in soil is the Lin pathway, and variants of this pathway will degrade all four of the HCH isomers although only slowly. Sequence differences in the primary LinA and LinB enzymes in the pathway play a key role in determining their ability to degrade the different isomers. LinA is a dehydrochlorinase, but little is known of its biochemistry. LinB is a hydrolytic dechlorinase that has been heterologously expressed and crystallized, and there is some understanding of the sequence-structure-function relationships underlying its substrate specificity and kinetics, although there are also some significant anomalies. The kinetics of some LinB variants are reported to be slow even for their preferred isomers. It is important to develop a better understanding of the biochemistries of the LinA and LinB variants and to use that knowledge to build better variants, because field trials of some bioremediation strategies based on the Lin pathway have yielded promising results but would not yet achieve economic levels of remediation.
authors.affiliation: Department of Zoology, University of Delhi, Delhi 110007, India. ruplal@gmail.com
authors.forename: Rup
authors.initials: R
authors.lastname: Lal
authors.forename: Gunjan
authors.initials: G
authors.lastname: Pandey
authors.forename: Pooja
authors.initials: P
authors.lastname: Sharma
authors.forename: Kirti
authors.initials: K
authors.lastname: Kumari
authors.forename: Shweta
authors.initials: S
authors.lastname: Malhotra
authors.forename: Rinku
authors.initials: R
authors.lastname: Pandey
authors.forename: Vishakha
authors.initials: V
authors.lastname: Raina
authors.forename: Hans-Peter E
authors.initials: HP
authors.lastname: Kohler
authors.forename: Christof
authors.initials: C
authors.lastname: Holliger
authors.forename: Colin
authors.initials: C
authors.lastname: Jackson
authors.forename: John G
authors.initials: JG
authors.lastname: Oakeshott
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001673:Biodegradation, Environmental; D001556:Hexachlorocyclohexane / Q000737:chemistry / Q000378:metabolism*; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D012988:Soil Microbiology; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D007306:Insecticides; D001556:Hexachlorocyclohexane