Important amino acid residues of hexachlorocyclohexane dehydrochlorinases (LinA) for enantioselective transformation of hexachlorocyclohexane isomers

• Published in: Biodegradation (Dordrecht) 2017-06, Vol.28 (2-3), p.171-180
• Main Authors: Shrivastava, Nidhi, Macwan, Ankit S., Kohler, Hans-Peter E., Kumar, Ashwani
• Format: Article
• Language: English
• Subjects: Amino acid sequence; Amino acids; Amino Acids - chemistry; Analysis; Aquatic Pollution; Biochemistry; Biodegradation, Environmental; Biomedical and Life Sciences; Chromatography, Gas; Docking; Enantiomers; Enzymes; Genetic transformation; Geochemistry; Hexachlorocyclohexane; Isomers; Life Sciences; Lindane - chemistry; Lindane - metabolism; Lyases - chemistry; Lyases - genetics; Lyases - metabolism; Microbiology; Mutant Proteins - metabolism; Mutation - genetics; Original Paper; Residues; Selective binding; Soil Science & Conservation; Stereoisomerism; Structure-Activity Relationship; Substrates; Terrestrial Pollution; Waste Management/Waste Technology; Waste Water Technology; Water Management; Water Pollution Control
• ISSN: 0923-9820; 1572-9729; 1572-9729
• DOI: 10.1007/s10532-017-9786-9

LinA-type1 and LinA-type2 are two well-characterized variants of the enzyme ‘hexachlorocyclohexane (HCH)-dehydrochlorinase’. They differ from each other at ten amino acid positions and exhibit differing enantioselectivity for the transformation of the (–) and (+) enantiomers of α-HCH. Amino acids responsible for this enantioselectivity, however, are not known. An in silico docking analysis identified four amino acids (K20, L96, A131, and T133) in LinA-type1 that could be involved in selective binding of the substrates. Experimental studies with constructed mutant enzymes revealed that a combined presence of three amino acid changes in LinA-type1, i.e. K20Q, L96C, and A131G, caused a reversal in its preference from the (–) to the (+) enantiomer of α-HCH. This preference was enhanced by the additional amino acid change T133 M. Presence of these four changes also caused the reversal of enantioselectivity of LinA-type1 for δ-HCH, and β-, γ-, and δ-pentachlorocyclohexens. Thus, the residues K20, L96, A131, and T133 in LinA-type1 and the residues Q20, C96, G131, and M133 in LinA-type 2 appear to be important determinants for the enantioselectivity of LinA enzymes.