Modern computational tools can predict the mutational effects on protein stability, sometimes at the expense of activity or solubility. Here, we investigate two homologous computationally stabilized haloalkane dehalogenases: (i) the soluble thermostable DhaA115 (Tmapp = 74 °C) and (ii) the poorly soluble and aggregating thermostable LinB116 (Tmapp = 65 °C), together with their respective wild-type variants. The intriguing difference in the solubility of these highly homologous proteins has remained unexplained for three decades. We combined experimental and in-silico techniques and examined the effects of stabilization on solubility and aggregation propensity. A detailed analysis of the unfolding mechanisms in the context of aggregation explained the negative consequences of stabilization observed in LinB116. With the aid of molecular dynamics simulations, we identified regions exposed during the unfolding of LinB116 that were later found to exhibit aggregation propensity. Our analysis identified cryptic aggregation-prone regions and increased surface hydrophobicity as key factors contributing to the reduced solubility of LinB116. This study reveals novel molecular mechanisms of unfolding for hyperstabilized dehalogenases and highlights the importance of contextual information in protein engineering to avoid the negative effects of stabilizing mutations on protein solubility.

• MeSH
• Hydrophobic and Hydrophilic Interactions MeSH
• Hydrolases * chemistry   metabolism   genetics   MeSH
• Protein Aggregates * MeSH
• Protein Unfolding * MeSH
• Solubility MeSH
• Molecular Dynamics Simulation MeSH
• Protein Stability MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• haloalkane dehalogenase MeSH Browser
• Hydrolases * MeSH
• Protein Aggregates * MeSH

Computational design of protein catalysts with enhanced stabilities for use in research and enzyme technologies is a challenging task. Using force-field calculations and phylogenetic analysis, we previously designed the haloalkane dehalogenase DhaA115 which contains 11 mutations that confer upon it outstanding thermostability (T m = 73.5 °C; ΔT m > 23 °C). An understanding of the structural basis of this hyperstabilization is required in order to develop computer algorithms and predictive tools. Here, we report X-ray structures of DhaA115 at 1.55 Å and 1.6 Å resolutions and their molecular dynamics trajectories, which unravel the intricate network of interactions that reinforce the αβα-sandwich architecture. Unexpectedly, mutations toward bulky aromatic amino acids at the protein surface triggered long-distance (∼27 Å) backbone changes due to cooperative effects. These cooperative interactions produced an unprecedented double-lock system that: (i) induced backbone changes, (ii) closed the molecular gates to the active site, (iii) reduced the volumes of the main and slot access tunnels, and (iv) occluded the active site. Despite these spatial restrictions, experimental tracing of the access tunnels using krypton derivative crystals demonstrates that transport of ligands is still effective. Our findings highlight key thermostabilization effects and provide a structural basis for designing new thermostable protein catalysts.

• Publication type
• Journal Article MeSH

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 α4 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 (ΔT m = -5 to 6 °C). 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 β-bromoalkanes. Our findings support a protein engineering strategy employing surface loop-helix transplantation for construction of novel protein catalysts with modified catalytic properties.

• Keywords
• Access tunnel, Biocatalysis, Enantioselectivity, Enzyme engineering, Haloalkane dehalogenase (HLD), Loop-helix transplantation, Protein design, X-ray crystallography,
• Publication type
• Journal Article MeSH

Haloalkane dehalogenases are enzymes that catalyze the cleavage of carbon-halogen bonds in halogenated compounds. They serve as model enzymes for studying structure-function relationships of >100.000 members of the α/β-hydrolase superfamily. Detailed kinetic analysis of their reaction is crucial for understanding the reaction mechanism and developing novel concepts in protein engineering. Fluorescent substrates, which change their fluorescence properties during a catalytic cycle, may serve as attractive molecular probes for studying the mechanism of enzyme catalysis. In this work, we present the development of the first fluorescent substrates for this enzyme family based on coumarin and BODIPY chromophores. Steady-state and pre-steady-state kinetics with two of the most active haloalkane dehalogenases, DmmA and LinB, revealed that both fluorescent substrates provided specificity constant two orders of magnitude higher (0.14-12.6 μM-1 s-1) than previously reported representative substrates for the haloalkane dehalogenase family (0.00005-0.014 μM-1 s-1). Stopped-flow fluorescence/FRET analysis enabled for the first time monitoring of all individual reaction steps within a single experiment: (i) substrate binding, (ii-iii) two subsequent chemical steps and (iv) product release. The newly introduced fluorescent molecules are potent probes for fast steady-state kinetic profiling. In combination with rapid mixing techniques, they provide highly valuable information about individual kinetic steps and mechanism of haloalkane dehalogenases. Additionally, these molecules offer high specificity and efficiency for protein labeling and can serve as probes for studying protein hydration and dynamics as well as potential markers for cell imaging.

• Keywords
• Enzyme kinetics, Fluorescent substrate, Haloalkane dehalogenase, Mechanism, Protein labeling,
• Publication type
• Journal Article MeSH

Halide assays are important for the study of enzymatic dehalogenation, a topic of great industrial and scientific importance. Here we describe the development of a very sensitive halide assay that can detect less than a picomole of bromide ions, making it very useful for quantifying enzymatic dehalogenation products. Halides are oxidised under mild conditions using the vanadium-dependent chloroperoxidase from Curvularia inaequalis, forming hypohalous acids that are detected using aminophenyl fluorescein. The assay is up to three orders of magnitude more sensitive than currently available alternatives, with detection limits of 20 nM for bromide and 1 μM for chloride and iodide. We demonstrate that the assay can be used to determine specific activities of dehalogenases and validate this by comparison to a well-established GC-MS method. This new assay will facilitate the identification and characterisation of novel dehalogenases and may also be of interest to those studying other halide-producing enzymes.

• Keywords
• dehalogenase, fluorescence, halides, haloalkane, haloperoxidase,
• Publication type
• Journal Article MeSH

Transport of ligands between bulk solvent and the buried active sites is a critical event in the catalytic cycle of many enzymes. The rational design of transport pathways is far from trivial due to the lack of knowledge about the effect of mutations on ligand transport. The main and an auxiliary tunnel of haloalkane dehalogenase LinB have been previously engineered for improved dehalogenation of 1,2-dibromoethane (DBE). The first chemical step of DBE conversion was enhanced by L177W mutation in the main tunnel, but the rate-limiting product release was slowed down because the mutation blocked the main access tunnel and hindered protein dynamics. Three additional mutations W140A + F143L + I211L opened-up the auxiliary tunnel and enhanced the product release, making this four-point variant the most efficient catalyst with DBE. Here we study the impact of these mutations on the catalysis of bulky aromatic substrates, 4-(bromomethyl)-6,7-dimethoxycoumarin (COU) and 8-chloromethyl-4,4'-difluoro-3,5-dimethyl-4-bora-3a,4a-diaza-s-indacene (BDP). The rate-limiting step of DBE conversion is the product release, whereas the catalysis of COU and BDP is limited by the chemical step. The catalysis of COU is mainly impaired by the mutation L177W, whereas the conversion of BDP is affected primarily by the mutations W140A + F143L + I211L. The combined computational and kinetic analyses explain the differences in activities between the enzyme-substrate pairs. The effect of tunnel mutations on catalysis depends on the rate-limiting step, the complementarity of the tunnels with the substrates and is clearly specific for each enzyme-substrate pair.

• Keywords
• BDP, 8-chloromethyl-3,5-dimethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, COU, 4-(bromomethyl)-6,7-dimethoxycoumarin, Enzyme kinetics, Enzyme mutation, MD, molecular dynamics, MSM, Markov state model, NAC, near-attack conformer, Substrate specificity,
• Publication type
• Journal Article MeSH

HotSpot Wizard is a web server used for the automated identification of hotspots in semi-rational protein design to give improved protein stability, catalytic activity, substrate specificity and enantioselectivity. Since there are three orders of magnitude fewer protein structures than sequences in bioinformatic databases, the major limitation to the usability of previous versions was the requirement for the protein structure to be a compulsory input for the calculation. HotSpot Wizard 3.0 now accepts the protein sequence as input data. The protein structure for the query sequence is obtained either from eight repositories of homology models or is modeled using Modeller and I-Tasser. The quality of the models is then evaluated using three quality assessment tools-WHAT_CHECK, PROCHECK and MolProbity. During follow-up analyses, the system automatically warns the users whenever they attempt to redesign poorly predicted parts of their homology models. The second main limitation of HotSpot Wizard's predictions is that it identifies suitable positions for mutagenesis, but does not provide any reliable advice on particular substitutions. A new module for the estimation of thermodynamic stabilities using the Rosetta and FoldX suites has been introduced which prevents destabilizing mutations among pre-selected variants entering experimental testing. HotSpot Wizard is freely available at http://loschmidt.chemi.muni.cz/hotspotwizard.

• MeSH
• Databases, Protein MeSH
• Internet * MeSH
• Catalytic Domain MeSH
• Models, Molecular MeSH
• Mutation MeSH
• Proteins chemistry   genetics   MeSH
• Amino Acid Sequence MeSH
• Sequence Alignment MeSH
• Software * MeSH
• Protein Stability MeSH
• Thermodynamics MeSH
• Computational Biology * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Proteins MeSH

The effect of non-denaturing concentrations of three different organic solvents, formamide, acetone and isopropanol, on the structure of haloalkane dehalogenases DhaA, LinB, and DbjA at the protein-solvent interface was studied using molecular dynamics simulations. Analysis of B-factors revealed that the presence of a given organic solvent mainly affects the dynamical behavior of the specificity-determining cap domain, with the exception of DbjA in acetone. Orientation of organic solvent molecules on the protein surface during the simulations was clearly dependent on their interaction with hydrophobic or hydrophilic surface patches, and the simulations suggest that the behavior of studied organic solvents in the vicinity of hyrophobic patches on the surface is similar to the air/water interface. DbjA was the only dimeric enzyme among studied haloalkane dehalogenases and provided an opportunity to explore effects of organic solvents on the quaternary structure. Penetration and trapping of organic solvents in the network of interactions between both monomers depends on the physico-chemical properties of the organic solvents. Consequently, both monomers of this enzyme oscillate differently in different organic solvents. With the exception of LinB in acetone, the structures of studied enzymes were stabilized in water-miscible organic solvents.

• MeSH
• 2-Propanol chemistry   pharmacology   MeSH
• Acetone chemistry   pharmacology   MeSH
• Formamides chemistry   pharmacology   MeSH
• Hydrophobic and Hydrophilic Interactions MeSH
• Hydrolases chemistry   MeSH
• Crystallography, X-Ray MeSH
• Protein Structure, Quaternary drug effects   MeSH
• Models, Molecular MeSH
• Solvents chemistry   MeSH
• Molecular Dynamics Simulation MeSH
• Protein Structure, Tertiary drug effects   MeSH
• Water chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 2-Propanol MeSH
• Acetone MeSH
• formamide MeSH Browser
• Formamides MeSH
• haloalkane dehalogenase MeSH Browser
• Hydrolases MeSH
• Solvents MeSH
• Water MeSH

• MeSH
• Enzymes chemistry   genetics   metabolism   MeSH
• Coenzymes chemistry   metabolism   MeSH
• Protein Conformation MeSH
• Protein Engineering methods   MeSH
• Recombinant Proteins chemistry   genetics   metabolism   MeSH
• Solvents MeSH
• Protein Structure, Tertiary MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Enzymes MeSH
• Coenzymes MeSH
• Recombinant Proteins MeSH
• Solvents MeSH

Haloalkane dehalogenases are microbial enzymes that convert a broad range of halogenated aliphatic compounds to their corresponding alcohols by the hydrolytic mechanism. These enzymes play an important role in the biodegradation of various environmental pollutants. Haloalkane dehalogenase LinB isolated from a soil bacterium Sphingobium japonicum UT26 has a relatively broad substrate specificity and can be applied in bioremediation and biosensing of environmental pollutants. The LinB variants presented here, LinB32 and LinB70, were constructed with the goal of studying the effect of mutations on enzyme functionality. In the case of LinB32 (L117W), the introduced mutation leads to blocking of the main tunnel connecting the deeply buried active site with the surrounding solvent. The other variant, LinB70 (L44I, H107Q), has the second halide-binding site in a position analogous to that in the related haloalkane dehalogenase DbeA from Bradyrhizobium elkanii USDA94. Both LinB variants were successfully crystallized and full data sets were collected for native enzymes as well as their complexes with the substrates 1,2-dibromoethane (LinB32) and 1-bromobutane (LinB70) to resolutions ranging from 1.6 to 2.8 Å. The two mutants crystallize differently from each other, which suggests that the mutations, although deep inside the molecule, can still affect the protein crystallizability.

• Keywords
• LinB, Sphingobium japonicum, haloalkane dehalogenase, macroseeding,
• MeSH
• Bacterial Proteins chemistry   genetics   metabolism   MeSH
• Biodegradation, Environmental MeSH
• Hydrocarbons, Brominated chemistry   metabolism   MeSH
• Escherichia coli chemistry   genetics   MeSH
• Ethylene Dibromide chemistry   metabolism   MeSH
• Hydrolases chemistry   genetics   metabolism   MeSH
• Isoenzymes chemistry   genetics   metabolism   MeSH
• Crystallization MeSH
• Crystallography, X-Ray MeSH
• Recombinant Proteins chemistry   genetics   metabolism   MeSH
• Sphingomonadaceae chemistry   enzymology   genetics   MeSH
• Substrate Specificity MeSH
• Binding Sites MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Hydrocarbons, Brominated MeSH
• butyl bromide MeSH Browser
• Ethylene Dibromide MeSH
• haloalkane dehalogenase MeSH Browser
• Hydrolases MeSH
• Isoenzymes MeSH
• Recombinant Proteins MeSH