(Below N is a link to NCBI taxonomic web page and E link to ESTHER at designed phylum.) > cellular organisms: NE > Bacteria: NE > Proteobacteria: NE > Alphaproteobacteria: NE > Rhizobiales: NE > Bradyrhizobiaceae: NE > Bradyrhizobium: NE > Bradyrhizobium elkanii: NE
LegendThis sequence has been compared to family alignement (MSA) red => minority aminoacid blue => majority aminoacid color intensity => conservation rate title => sequence position(MSA position)aminoacid rate Catalytic site Catalytic site in the MSA MTISADISLHHRAVLGSTMAYRETGRSDAPHVLFLHGNPTSSYIWRNIMP LVAPVGHCIAPDLIGYGQSGKPDISYRFFDQADYLDALIDELGIASAYLV AQDWGTALAFHLAARRPQLVRGLAFMEFIRPMRDWSDFHQHDAARETFRK FRTPGVGEAMILDNNAFVERVLPGSILRTLSEEEMAAYRAPFATRESRMP TLMLPRELPIAGEPADVTQALTAAHAALAASTYPKLLFVGSPGALVSPAF AAEFAKTLKHCAVIQLGAGGHYLQEDHPEAIGRSVAGWIAGIEAASAQRH AACRAKRART
Haloalkane dehalogenases are a very important class of microbial enzymes for environmental detoxification of halogenated pollutants, for biocatalysis, biosensing and molecular tagging. The double mutant (Ile44Leu + Gln102His) of the haloalkane dehalogenase DbeA from Bradyrhizobium elkanii USDA94 (DbeADCl) was constructed to study the role of the second halide-binding site previously discovered in the wild-type structure. The variant is less active, less stable in the presence of chloride ions and exhibits significantly altered substrate specificity when compared with the DbeAwt. DbeADCl was crystallized using the sitting-drop vapour-diffusion procedure with further optimization by the random microseeding technique. The crystal structure of the DbeADCl has been determined and refined to the 1.4 A resolution. The DbeADCl crystals belong to monoclinic space group C121. The DbeADCl molecular structure was characterized and compared with five known haloalkane dehalogenases selected from the Protein Data Bank
An enzyme's substrate specificity is one of its most important characteristics. The quantitative comparison of broad-specificity enzymes requires the selection of a homogenous set of substrates for experimental testing, determination of substrate-specificity data and analysis using multivariate statistics. We describe a systematic analysis of the substrate specificities of nine wild-type and four engineered haloalkane dehalogenases. The enzymes were characterized experimentally using a set of 30 substrates selected using statistical experimental design from a set of nearly 200 halogenated compounds. Analysis of the activity data showed that the most universally useful substrates in the assessment of haloalkane dehalogenase activity are 1-bromobutane, 1-iodopropane, 1-iodobutane, 1,2-dibromoethane and 4-bromobutanenitrile. Functional relationships among the enzymes were explored using principal component analysis. Analysis of the untransformed specific activity data revealed that the overall activity of wild-type haloalkane dehalogenases decreases in the following order: LinB~DbjA>DhlA~DhaA~DbeA~DmbA>DatA~DmbC~DrbA. After transforming the data, we were able to classify haloalkane dehalogenases into four SSGs (substrate-specificity groups). These functional groups are clearly distinct from the evolutionary subfamilies, suggesting that phylogenetic analysis cannot be used to predict the substrate specificity of individual haloalkane dehalogenases. Structural and functional comparisons of wild-type and mutant enzymes revealed that the architecture of the active site and the main access tunnel significantly influences the substrate specificity of these enzymes, but is not its only determinant. The identification of other structural determinants of the substrate specificity remains a challenge for further research on haloalkane dehalogenases.
A novel enzyme, DbeA, belonging to the haloalkane dehalogenase family (EC 3.8.1.5) was isolated from Bradyrhizobium elkani USDA94. This haloalkane dehalogenase is closely related to the DbjA enzyme from B. japonicum USDA110 (71% sequence identity), but has different biochemical properties. DbeA is generally less active and has a higher specificity towards brominated and iodinated compounds than DbjA. In order to understand the altered activity and specificity of DbeA, its mutant variant DbeA1, which carries the unique fragment of DbjA, was also constructed. Both wild-type DbeA and DbeA1 were crystallized using the sitting-drop vapour-diffusion method. The crystals of DbeA belonged to the primitive orthorhombic space group P2(1)2(1)2(1), while the crystals of DbeA1 belonged to the monoclinic space group C2. Diffraction data were collected to 2.2 A resolution for both DbeA and DbeA1 crystals.
Engineering enzyme catalytic properties is important for basic research as well as for biotechnological applications. We have previously shown that the reshaping of enzyme access tunnels via the deletion of a short surface loop element may yield a haloalkane dehalogenase variant with markedly modified substrate specificity and enantioselectivity. Here, we conversely probed the effects of surface loop-helix transplantation from one enzyme to another within the enzyme family of haloalkane dehalogenases. Precisely, we transplanted a nine-residue long extension of L9 loop and beta4 helix from DbjA into the corresponding site of DbeA. Biophysical characterization showed that this fragment transplantation did not affect the overall protein fold or oligomeric state, but lowered protein stability (DeltaT (m) = -5 to 6 degC). Interestingly, the crystal structure of DbeA mutant revealed the unique structural features of enzyme access tunnels, which are known determinants of catalytic properties for this enzyme family. Biochemical data confirmed that insertion increased activity of DbeA with various halogenated substrates and altered its enantioselectivity with several linear beta-bromoalkanes. Our findings support a protein engineering strategy employing surface loop-helix transplantation for construction of novel protein catalysts with modified catalytic properties.
Haloalkane dehalogenases are a very important class of microbial enzymes for environmental detoxification of halogenated pollutants, for biocatalysis, biosensing and molecular tagging. The double mutant (Ile44Leu + Gln102His) of the haloalkane dehalogenase DbeA from Bradyrhizobium elkanii USDA94 (DbeADCl) was constructed to study the role of the second halide-binding site previously discovered in the wild-type structure. The variant is less active, less stable in the presence of chloride ions and exhibits significantly altered substrate specificity when compared with the DbeAwt. DbeADCl was crystallized using the sitting-drop vapour-diffusion procedure with further optimization by the random microseeding technique. The crystal structure of the DbeADCl has been determined and refined to the 1.4 A resolution. The DbeADCl crystals belong to monoclinic space group C121. The DbeADCl molecular structure was characterized and compared with five known haloalkane dehalogenases selected from the Protein Data Bank
The crystal structure of the novel haloalkane dehalogenase DbeA from Bradyrhizobium elkanii USDA94 revealed the presence of two chloride ions buried in the protein interior. The first halide-binding site is involved in substrate binding and is present in all structurally characterized haloalkane dehalogenases. The second halide-binding site is unique to DbeA. To elucidate the role of the second halide-binding site in enzyme functionality, a two-point mutant lacking this site was constructed and characterized. These substitutions resulted in a shift in the substrate-specificity class and were accompanied by a decrease in enzyme activity, stability and the elimination of substrate inhibition. The changes in enzyme catalytic activity were attributed to deceleration of the rate-limiting hydrolytic step mediated by the lower basicity of the catalytic histidine.
An enzyme's substrate specificity is one of its most important characteristics. The quantitative comparison of broad-specificity enzymes requires the selection of a homogenous set of substrates for experimental testing, determination of substrate-specificity data and analysis using multivariate statistics. We describe a systematic analysis of the substrate specificities of nine wild-type and four engineered haloalkane dehalogenases. The enzymes were characterized experimentally using a set of 30 substrates selected using statistical experimental design from a set of nearly 200 halogenated compounds. Analysis of the activity data showed that the most universally useful substrates in the assessment of haloalkane dehalogenase activity are 1-bromobutane, 1-iodopropane, 1-iodobutane, 1,2-dibromoethane and 4-bromobutanenitrile. Functional relationships among the enzymes were explored using principal component analysis. Analysis of the untransformed specific activity data revealed that the overall activity of wild-type haloalkane dehalogenases decreases in the following order: LinB~DbjA>DhlA~DhaA~DbeA~DmbA>DatA~DmbC~DrbA. After transforming the data, we were able to classify haloalkane dehalogenases into four SSGs (substrate-specificity groups). These functional groups are clearly distinct from the evolutionary subfamilies, suggesting that phylogenetic analysis cannot be used to predict the substrate specificity of individual haloalkane dehalogenases. Structural and functional comparisons of wild-type and mutant enzymes revealed that the architecture of the active site and the main access tunnel significantly influences the substrate specificity of these enzymes, but is not its only determinant. The identification of other structural determinants of the substrate specificity remains a challenge for further research on haloalkane dehalogenases.
A novel enzyme, DbeA, belonging to the haloalkane dehalogenase family (EC 3.8.1.5) was isolated from Bradyrhizobium elkani USDA94. This haloalkane dehalogenase is closely related to the DbjA enzyme from B. japonicum USDA110 (71% sequence identity), but has different biochemical properties. DbeA is generally less active and has a higher specificity towards brominated and iodinated compounds than DbjA. In order to understand the altered activity and specificity of DbeA, its mutant variant DbeA1, which carries the unique fragment of DbjA, was also constructed. Both wild-type DbeA and DbeA1 were crystallized using the sitting-drop vapour-diffusion method. The crystals of DbeA belonged to the primitive orthorhombic space group P2(1)2(1)2(1), while the crystals of DbeA1 belonged to the monoclinic space group C2. Diffraction data were collected to 2.2 A resolution for both DbeA and DbeA1 crystals.
Bradyrhizobium elkanii haloalkane dehalogenase (EC 3.8.1.5) DbeA
