Haloalkane dehalogenase

Figure C2.7.8. Catalytic cycle indicating the working of tire enzyme haloalkane dehalogenase [11],...

Verschueren K H G, Seljee F, Rozeboom J, Kalk K H and Dijkstra B W 1993 Crystallographic analysis of the catalytic mechanism of haloalkane dehalogenase Nature 363 693-8... 

Nucleophilic substitution is one of a variety of mechanisms by which living systems detoxify halogenated organic compounds introduced into the environment Enzymes that catalyze these reactions are known as haloalkane dehalogenases The hydrolysis of 1 2 dichloroethane to 2 chloroethanol for example is a biological nude ophilic substitution catalyzed by a dehalogenase... 

Ring opening of epoxides with nucleophiles other than water (Cl, BrT I, NOz , CN ) can also be catalyzed by halohydrin dehalogenase enzymes (EC 3.8.1.5, also named haloalkane dehalogenase or haloalcohd dehalogenase) (Figure 6.74) [197]. 

Jesenska A, M Bartos, V Czernekova, I Rychh k, I Pavlik, J Damborsky (2002) Cloning and expression of the haloalkane dehalogenase gene dhmA from Mycobacterium avium N85 and preliminary characterization of DhmA. Appl Environ Microbiol 68 3224-3230. 

Bosma T, E Kruizinga, EJ de Bruin, GJ Poelarends, DB Janssen (1999) Utilization of trihalogenated propanes by Agrobacterium radiobacter ADI through heterologous expression of the haloalkane dehalogenase from Rhododoccus sp. strain ml5-3. Appl Environ Microbiol 65 4575-4581. 

Bosma T, J Damborsky, G Stucki, DB Janssen (2002) Biodegradation of 1,2,3-trichloropropane through directed evolution and heterologous expression of a haloalkane dehalogenase gene. Appl Environ Microbiol 68 3582-3587. 

Jesenska A, M Pavlova, M Strouhal, R Chaloupkova, I Tesmska, M Monincova, Z Prokop, M Bartos, 1 Pavlik, 1 Rychllk, P Mdbius, Y Nagata, J Damborsky (2005) Cloning, biochemical properties, and distribution of mycobacterial haloalkane dehalogenases. Appl Environ Microbiol 71 6736-6745. 

Keuning S, DB Janssen, B Witholt (1985) Purification and characterization of hydrolytic haloalkane dehalogenase from Xanthobacter autotrophicus GJ 10. J Bacterial 163 635-639. 

Nagata Y, Z Prokop, Y Sato, P Jerabek, A Kumar, Y Ohtsubo, M Tsuda, J Damborsky (2005) Degradation of b-hexachlorocyclohexane by haloalkane dehalogenase LinB from Sphingomonas paucimobilis UT 26. Appl Environ Microbiol 71 2183-2185. 

Sharma P, V Raina, R Kumari, S Malhotra, C Dogra, H Kumari, H-P E Kohler, H-R Buser, C Holliger, R Lai (2006) Haloalkane dehalogenase LinB is responsible for [5- and 5-hexachlorocyclohexane transformation in Sphingobium indicum B90A. Appl Environ Microbiol 72 5720-5727. 

Lewandowicz A, J Rudzinski, L Tronstad, M Widersten, P Ryberg, O Matsson, P Paneth (2001) Chlorine isotope effects on the haloalkane dehalogenase reaction. J Am Chem Soc 123 4550-4555. 

For heavy atom isotope effects tunneling is relatively unimportant and the TST model suffices. As an example the dehalogenation of 1,2-dichloroethane (DCE) to 2-chloroethanol catalyzed by haloalkane dehalogenase DhlA is discussed below. This example has been chosen because the chlorine kinetic isotope effect for this reaction has been computed using three different schemes, and this system is among the most thoroughly studied examples of heavy atom isotope effects in enzymatic reactions. 

The haloalkane dehalogenase DhlA mechanism takes place in two consecutive Sn2 steps. In the first, the carboxylate moiety of the aspartate Aspl24, acting as a nucleophile on the carbon atom of DCE, displaces chloride anion which leads to formation of the enzyme-substrate intermediate (Equation 11.86). That intermediate is hydrolyzed by water in the subsequent step. The experimentally determined chlorine kinetic isotope effect for 1-chlorobutane, the slow substrate, is k(35Cl)/k(37Cl) = 1.0066 0.0004 and should correspond to the intrinsic isotope effect for the dehalogenation step. While the reported experimental value for DCE hydrolysis is smaller, it becomes practically the same when corrected for the intramolecular chlorine kinetic isotope effect (a consequence of the two identical chlorine labels in DCE). 

Amino acid sequence relationships have suggested a number of HYL families based on percent identity, enzymes with >40% identity belonging to the same family [48]. Families so identified include the mammalian microsomal EH (HYL1), the mammalian cytosolic EH (HYL2), the plant cytosolic EH (HYL3), and bacterial C-X bond hydrolases (haloacid dehydrogenases, HAD, and haloalkane dehalogenases, HLD). 

Fig. 11.4. Catalytic cycle of the haloalkane dehalogenase of Xanthobacter autotrophicus... 

J. P. Schanstra, D. B. Janssen, Kinetics of Halide Release of Haloalkane Dehalogenase Evidence for a Slow Conformational Change , Biochemistry 1996, 35, 5624 - 5632 J. 

Scheme 6. Mechanism of microsomal epoxide hydrolase and of haloalkane dehalogenase...

Molecular dynamics simulations of ground and transition states have been carried out for the n2 displacement of chloride ion from 1,2-dichloroethane by the Asp 124-C02 at the active site of Xanthobacter autotrophicus haloalkane dehalogenase. ... 

Haloalkane dehalogenase from Rhodococcus rhodocrous Dehalogenation reaction Dravis et al., 2000 [47]... 

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