Application of Rigidity Theory to the Thermostabilization of Lipase A from Bacillus subtilis

The two-step strategy for enhancing the specific activity and thermostability of alginate lyase AlyG2 with mechanism for improved thermostability

To overcome the trade-off challenge encountered in the engineering of alginate lyase AlyG2 from Seonamhaeicola algicola Gy8T and to expand its potential industrial applications, we devised a two-step strategy encompassing activity enhancement followed by thermal stability engineering. To enhance the specific activity of efficient AlyG2, we strategically substituted residues with bulky steric hindrance proximal to the active pocket with glycine or alanine. This led to the generation of three promising positive mutants, with particular emphasis on the T91S mutant, exhibiting a 1.91-fold specific activity compared to the wild type. To mitigate the poor thermal stability of T91S, mutants with negative ΔΔG values in the thermal flexibility region were screened out. Notably, the S72Ya mutant not only displayed 17.96 % further increase in specific activity but also exhibited improved stability compared to T91S, manifesting as a remarkable 30.97 % increase in relative activity following a 1-hour incubation at 42 °C. Furthermore, enhanced kinetic stability was observed. To gain deeper insights into the mechanism underlying the enhanced thermostability of the S72Ya mutant, we conducted molecular dynamics simulations, principal component analysis (PCA), dynamic cross-correlation map (DCCM), and free energy landscape (FEL) analysis. The results unveiled a reduction in the flexibility of the surface loop, a stronger correlation dynamic and a narrower motion subspace in S72Ya system, along with the formation of more stable hydrogen bonds. Collectively, our findings suggest amino acids substitutions resulting in smaller side chains proximate to the active site can positively impact enzyme activity, while reducing the flexibility of surface loops emerges as a pivotal factor in conferring thermal stability. These insights offer valuable guidance and a framework for the engineering of other enzyme types.

Enzyme engineering for functional lipids synthesis: recent advance and perspective

Functional lipids, primarily derived through the modification of natural lipids by various processes, are widely acknowledged for their potential to impart health benefits. In contrast to chemical methods for lipid modification, enzymatic catalysis offers distinct advantages, including high selectivity, mild operating conditions, and reduced byproduct formation. Nevertheless, enzymes face challenges in industrial applications, such as low activity, stability, and undesired selectivity. To address these challenges, protein engineering techniques have been implemented to enhance enzyme performance in functional lipid synthesis. This article aims to review recent advances in protein engineering, encompassing approaches from directed evolution to rational design, with the goal of improving the properties of lipid-modifying enzymes. Furthermore, the article explores the future prospects and challenges associated with enzyme-catalyzed functional lipid synthesis.

Accelerated molecular dynamics study to compare the thermostability of Bacillus licheniformis and Aspergillus niger α-amylase

The thermostability of enzymes plays a significant role in the starch hydrolysis process in the industry. The structural difference between thermostable Bacillus licheniformis α-amylase (BLA) and thermolabile Aspergillus niger α-amylase (ANA) is interesting to be explored. This work aimed to study the thermostability-determining factor of BLA as compared to a non-thermostable enzyme, ANA, using molecular dynamics (MD) simulation at a high temperature. A 100 ns of classical MD, which was followed by 200 ns accelerated MD was conducted to explore the conformational changes of the enzyme. It is revealed that the intramolecular interactions through salt bridge interactions and the presence of calcium ions dominates the stability effect of BLA, despite the absence of a disulfide bond in the structure. These results should be useful in designing a thermostable enzyme that can be used in industrial processes.Communicated by Ramaswamy H. Sarma.

Enzyme adaptation to habitat thermal legacy shapes the thermal plasticity of marine microbiomes

Microbial communities respond to temperature with physiological adaptation and compositional turnover. Whether thermal selection of enzymes explains marine microbiome plasticity in response to temperature remains unresolved. By quantifying the thermal behaviour of seven functionally-independent enzyme classes (esterase, extradiol dioxygenase, phosphatase, beta-galactosidase, nuclease, transaminase, and aldo-keto reductase) in native proteomes of marine sediment microbiomes from the Irish Sea to the southern Red Sea, we record a significant effect of the mean annual temperature (MAT) on enzyme response in all cases. Activity and stability profiles of 228 esterases and 5 extradiol dioxygenases from sediment and seawater across 70 locations worldwide validate this thermal pattern. Modelling the esterase phase transition temperature as a measure of structural flexibility confirms the observed relationship with MAT. Furthermore, when considering temperature variability in sites with non-significantly different MATs, the broadest range of enzyme thermal behaviour and the highest growth plasticity of the enriched heterotrophic bacteria occur in samples with the widest annual thermal variability. These results indicate that temperature-driven enzyme selection shapes microbiome thermal plasticity and that thermal variability finely tunes such processes and should be considered alongside MAT in forecasting microbial community thermal response.

Accurate Prediction of Enzyme Thermostabilization with Rosetta Using AlphaFold Ensembles

Thermostability enhancement is a fundamental aspect of protein engineering as a biocatalyst's half-life is key for its industrial and biotechnological application, particularly at high temperatures and under harsh conditions. Thermostability changes upon mutation originate from modifications of the free energy of unfolding (ΔG_u), making thermostabilization extremely challenging to predict with computational methods. In this contribution, we combine global conformational sampling with energy prediction using AlphaFold and Rosetta to develop a new computational protocol for the quantitative prediction of thermostability changes upon laboratory evolution of acyltransferase LovD and lipase LipA. We highlight how using an ensemble of protein conformations rather than a single three-dimensional model is mandatory for accurate thermostability predictions. By comparing our approaches with existing ones, we show that ensembles based on AlphaFold models provide more accurate and robust calculated thermostability trends than ensembles based solely on crystallographic structures as the latter introduce a strong distortion (scaffold bias) in computed thermostabilities. Eliminating this bias is critical for computer-guided enzyme design and evaluating the effect of multiple mutations on protein stability.

Glycine Substitution of Residues with Unfavored Dihedral Angles Improves Protein Thermostability

Single mutations that can substantially enhance stability are highly desirable for protein engineering. However, it is generally rare for this kind of mutant to emerge from directed evolution experiments. This study used computational approaches to identify hotspots in a diacylglycerol-specific lipase for mutagenesis with functional hotspot and sequence consensus strategies, followed by ∆∆G calculations for all possible mutations using the Rosetta ddg_monomer protocol. Single mutants with significant ∆∆G changes (≤−2.5 kcal/mol) were selected for expression and characterization. Three out of seven tested mutants showed a significantly enhanced thermostability, with Q282W and A292G in the catalytic pocket and D245G located on the opposite surface of the protein. Remarkably, A292G increased the T5015 (the temperature at which 50% of the enzyme activity was lost after a 15 min of incubation) by ~7 °C, concomitant with a twofold increase in enzymatic activity at the optimal reaction temperature. Structural analysis showed that both A292 and D245 adopted unfavored dihedral angles in the wild-type (WT) enzyme. Substitution of them by glycine might release a steric strain to increase the stability. In sum, substitution by glycine might be a promising strategy to improve protein thermostability.

Structure and Function of Redox-Sensitive Superfolder Green Fluorescent Protein Variant

Aims: Genetically encoded green fluorescent protein (GFP)-based redox biosensors are widely used to monitor specific and dynamic redox processes in living cells. Over the last few years, various biosensors for a variety of applications were engineered and enhanced to match the organism and cellular environments, which should be investigated. In this context, the unicellular intraerythrocytic parasite Plasmodium, the causative agent of malaria, represents a challenge, as the small size of the organism results in weak fluorescence signals that complicate precise measurements, especially for cell compartment-specific observations. To address this, we have functionally and structurally characterized an enhanced redox biosensor superfolder roGFP2 (sfroGFP2). Results: SfroGFP2 retains roGFP2-like behavior, yet with improved fluorescence intensity (FI) in cellulo. SfroGFP2-based redox biosensors are pH insensitive in a physiological pH range and show midpoint potentials comparable with roGFP2-based redox biosensors. Using crystallography and rigidity theory, we identified the superfolding mutations as being responsible for improved structural stability of the biosensor in a redox-sensitive environment, thus explaining the improved FI in cellulo. Innovation: This work provides insight into the structure and function of GFP-based redox biosensors. It describes an improved redox biosensor (sfroGFP2) suitable for measuring oxidizing effects within small cells where applicability of other redox sensor variants is limited. Conclusion: Improved structural stability of sfroGFP2 gives rise to increased FI in cellulo. Fusion to hGrx1 (human glutaredoxin-1) provides the hitherto most suitable biosensor for measuring oxidizing effects in Plasmodium. This sensor is of major interest for studying glutathione redox changes in small cells, as well as subcellular compartments in general. Antioxid. Redox Signal. 37, 1-18.

Extremophilic lipases for industrial applications: A general review

With industrialization and development in modern science enzymes and their applications increased widely. There is always a hunt for new proficient enzymes with novel properties to meet specific needs of various industrial sectors. Along with the high efficiency, the green and eco-friendly side of enzymes attracts human attention, as they form a true answer to counter the hazardous and toxic conventional industrial catalyst. Lipases have always earned industrial attention due to the broad range of hydrolytic and synthetic reactions they catalyse. When these catalytic properties get accompanied by features like temperature stability, pH stability, and solvent stability lipases becomes an appropriate tool for use in many industrial processes. Extremophilic lipases offer the same, thermostable: hot and cold active thermophilic and psychrophilic lipases, acid and alkali resistant and active acidophilic and alkaliphilic lipases, and salt tolerant halophilic lipases form excellent biocatalyst for detergent formulations, biofuel synthesis, ester synthesis, food processing, pharmaceuticals, leather, and paper industry. An interesting application of these lipases is in the bioremediation of lipid waste in harsh environments. The review gives a brief account on various extremophilic lipases with emphasis on thermophilic, psychrophilic, halophilic, alkaliphilic, and acidophilic lipases, their sources, biochemical properties, and potential applications in recent decades.

Insights of conformational dynamics on catalytic activity in the computational stability design of Bacillus subtilis LipA

In protein engineering, the contributions of individual mutations to designed combinatorial mutants are unpredictable. Screening designed mutations that affect enzyme catalytic activity enables evolutions towards efficient activities. Here, Bacillus subtilis LipA (BSLA) was selected as a model protein for thermostabilization designs, and the circular dichroism measurements showed six combinatorial designs with improved stability (from 5.81 °C to 13.61 °C). Based on molecular dynamic simulations, the conformational dynamics of the mutants revealed that mutations alter the populations of conformational states and the increased ensembles of inactive conformations might lead to a reduction in activity. We further demonstrated that the mutations responsible for the reduced enzyme catalytic activity involved a short dynamic correlation path to disturbing the equilibrium conformation of active sites. By removing N82V, which had a close dynamic correlation to the active sites in mutant D3, the redesigned mutant RD3 had an increased activity of 57.6%. By combining computational simulation with experimental verification, this work established that essential sites to counteract the activity-stability trade-off in multipoint combinatorial mutants could be computationally predicted and thus provide a possible strategy by which to indirectly or directly guide protein design.

Critical assessment of structure-based approaches to improve protein resistance in aqueous ionic liquids by enzyme-wide saturation mutagenesis

Ionic liquids (IL) and aqueous ionic liquids (aIL) are attractive (co-)solvents for green industrial processes involving biocatalysts, but often reduce enzyme activity. Experimental and computational methods are applied to predict favorable substitution sites and, most often, subsequent site-directed surface charge modifications are introduced to enhance enzyme resistance towards aIL. However, almost no studies evaluate the prediction precision with random mutagenesis or the application of simple data-driven filtering processes. Here, we systematically and rigorously evaluated the performance of 22 previously described structure-based approaches to increase enzyme resistance to aIL based on an experimental complete site-saturation mutagenesis library of Bacillus subtilis Lipase A (BsLipA) screened against four aIL. We show that, surprisingly, most of the approaches yield low gain-in-precision (GiP) values, particularly for predicting relevant positions: 14 approaches perform worse than random mutagenesis. Encouragingly, exploiting experimental information on the thermostability of BsLipA or structural weak spots of BsLipA predicted by rigidity theory yields GiP = 3.03 and 2.39 for relevant variants and GiP = 1.61 and 1.41 for relevant positions. Combining five simple-to-compute physicochemical and evolutionary properties substantially increases the precision of predicting relevant variants and positions, yielding GiP = 3.35 and 1.29. Finally, combining these properties with predictions of structural weak spots identified by rigidity theory additionally improves GiP for relevant variants up to 4-fold to ∼10 and sustains or increases GiP for relevant positions, resulting in a prediction precision of ∼90% compared to ∼9% in random mutagenesis. This combination should be applicable to other enzyme systems for guiding protein engineering approaches towards improved aIL resistance.

F/G Region Rigidity is Inversely Correlated to Substrate Promiscuity of Human CYP Isoforms Involved in Metabolism

Of 57 human cytochrome P450 (CYP) enzymes, 12 metabolize 90% of xenobiotics. To our knowledge, no study has addressed the relation between enzyme dynamics and substrate promiscuity for more than three CYPs. Here, we show by constraint dilution simulations with the Constraint Network Analysis for the 12 isoforms that structural rigidity of the F/G region is significantly inversely correlated to the enzymes' substrate promiscuity. This highlights the functional importance of structural dynamics of the substrate tunnel.

Aqueous ionic liquids redistribute local enzyme stability via long-range perturbation pathways

Ionic liquids (IL) and aqueous ionic liquids (aIL) are attractive (co-)solvents for biocatalysis due to their unique properties. On the other hand, the incubation of enzymes in IL or aIL often reduces enzyme activity. Recent studies proposed various aIL-induced effects to explain the reduction, classified as direct effects, e.g., local dehydration or competitive inhibition, and indirect effects, e.g., structural perturbations or disturbed catalytic site integrity. However, the molecular origin of indirect effects has largely remained elusive. Here we show by multi-μs long molecular dynamics simulations, free energy computations, and rigidity analyses that aIL favorably interact with specific residues of Bacillus subtilis Lipase A (BsLipA) and modify the local structural stability of this model enzyme by inducing long-range perturbations of noncovalent interactions. The perturbations percolate over neighboring residues and eventually affect the catalytic site and the buried protein core. Validation against a complete experimental site saturation mutagenesis library of BsLipA (3620 variants) reveals that the residues of the perturbation pathways are distinguished sequence positions where substitutions highly likely yield significantly improved residual activity. Our results demonstrate that identifying these perturbation pathways and specific IL ion-residue interactions there effectively predicts focused variant libraries with improved aIL tolerance.

Enhancing the thermostability of a mono- and diacylglycerol lipase from Malassizia globose by stabilizing a flexible loop in the catalytic pocket

A lipase from Malassizia globose, named SMG1, is highly desirable for industrial application due to its substrate specificity towards mono- and diacylglycerol. To improve its thermostability, we constructed a mutant library using an error-prone polymerase chain reaction, which was screened for both initial and residual enzymatic activity. Selected mutants were further studied using purified proteins for their kinetic thermostability at 45 ℃, T₅₀ (the temperature at which the enzyme loses half of its activity), and the optimal reaction temperature. Results showed that the majority of mutations with improved thermostability were on the protein surface. D245N and L270P showed the most significant thermostability enhancement with an approximately 3 ℃ increase in T₅₀ compared to wild-type (WT). In addition, combining these two mutations resulted in an increase of T₅₀ by 5 °C. Also, the optimal reaction temperatures of L270P and this double mutant are 10 ℃ higher than WT. The double mutant showed an approximately 100-fold increase in half-life at 45 ℃ and higher enzymatic activities at 30 ℃ and above compared to WT. High-temperature unfolding molecular dynamics simulation suggested that the double mutant stabilized a flexible loop in the catalytic pocket.

Less Unfavorable Salt Bridges on the Enzyme Surface Result in More Organic Cosolvent Resistance

Biocatalysis for the synthesis of fine chemicals is highly attractive but usually requires organic (co-)solvents (OSs). However, native enzymes often have low activity and resistance in OSs and at elevated temperatures. Herein, we report a smart salt bridge design strategy for simultaneously improving OS resistance and thermostability of the model enzyme, Bacillus subtilits Lipase A (BSLA). We combined comprehensive experimental studies of 3450 BSLA variants and molecular dynamics simulations of 36 systems. Iterative recombination of four beneficial substitutions yielded superior resistant variants with up to 7.6-fold (D64K/D144K) improved resistance toward three OSs while exhibiting significant thermostability (thermal resistance up to 137-fold, and half-life up to 3.3-fold). Molecular dynamics simulations revealed that locally refined flexibility and strengthened hydration jointly govern the highly increased resistance in OSs and at 50-100 °C. The salt bridge redesign provides protein engineers with a powerful and likely general approach to design OSs- and/or thermal-resistant lipases and other α/β-hydrolases.

Promiscuous Esterases Counterintuitively Are Less Flexible than Specific Ones

Understanding mechanisms of promiscuity is increasingly important from a fundamental and application point of view. As to enzyme structural dynamics, more promiscuous enzymes generally have been recognized to also be more flexible. However, examples for the opposite received much less attention. Here, we exploit comprehensive experimental information on the substrate promiscuity of 147 esterases tested against 96 esters together with computationally efficient rigidity analyses to understand the molecular origin of the observed promiscuity range. Unexpectedly, our data reveal that promiscuous esterases are significantly less flexible than specific ones, are significantly more thermostable, and have a significantly increased specific activity. These results may be reconciled with a model according to which structural flexibility in the case of specific esterases serves for conformational proofreading. Our results signify that an esterase sequence space can be screened by rigidity analyses for promiscuous esterases as starting points for further exploration in biotechnology and synthetic chemistry.

Can constraint network analysis guide the identification phase of KnowVolution? A case study on improved thermostability of an endo-β-glucanase

Cellulases are industrially important enzymes, e.g., in the production of bioethanol, in pulp and paper industry, feedstock, and textile. Thermostability is often a prerequisite for high process stability and improving thermostability without affecting specific activities at lower temperatures is challenging and often time-consuming. Protein engineering strategies that combine experimental and computational are emerging in order to reduce experimental screening efforts and speed up enzyme engineering campaigns. Constraint Network Analysis (CNA) is a promising computational method that identifies beneficial positions in enzymes to improve thermostability. In this study, we compare CNA and directed evolution in the identification of beneficial positions in order to evaluate the potential of CNA in protein engineering campaigns (e.g., in the identification phase of KnowVolution). We engineered the industrially relevant endoglucanase EGLII from Penicillium verruculosum towards increased thermostability. From the CNA approach, six variants were obtained with an up to 2-fold improvement in thermostability. The overall experimental burden was reduced to 40% utilizing the CNA method in comparison to directed evolution. On a variant level, the success rate was similar for both strategies, with 0.27% and 0.18% improved variants in the epPCR and CNA-guided library, respectively. In essence, CNA is an effective method for identification of positions that improve thermostability.

Isolation of novel Lactobacillus with lipolytic activity from the vinasse and their preliminary potential using as probiotics

Lactobacillus casei f1, L. paracasei f2 and L. paracasei f3 with lipolytic activity were isolated and identified from vinasses according to the morphological–physiological properties detection and 16S rDNA analysis. These three strains showed obvious lipase activities to olive oil and L. casei f1 performed highest enzyme activity of 17.8 U/mL. L. casei f1, L. paracasei f2 and L. paracasei f3 could lipolyze the blending oils, peanut oil and sesame oil with diverse degrading rates. The degrading rates to the preferred oils, L. casei f1 to blending oils, L. paracasei f2 to peanut oil and L. paracasei f3 to sesame oil, were 21.2%, 27.3% and 39.6%, respectively. The corresponding oil degrading rates increased as the cell growth and the highest degrading rates were obtained at the stationary phase with the viable count more than 7.5 LogCFU/mL. By GC–MS analysis, L. casei f1, L. paracasei f2 and L. paracasei f3 performed diverse lipolytic capacities to the 12 kinds of fat acids and all of them preferred to hydrolyze the linoleic acid with the degrading rate of 49.11%, 31.83% and 64.44%, respectively. These three strains showed considerable probiotic properties, displaying higher than 10⁶ CFU/mL desirable viable count though the simulated gastrointestinal tract, as well as inhibiting six indicator bacteria. These results suggested that the three isolated strains could be considered as novel probiotic candidates and applied in the food industry.

The acid-base-nucleophile catalytic triad in ABH-fold enzymes is coordinated by a set of structural elements

The alpha/beta-Hydrolases (ABH) are a structural class of proteins that are found widespread in nature and includes enzymes that can catalyze various reactions in different substrates. The catalytic versatility of the ABH fold enzymes, which has been a valuable property in protein engineering applications, is based on a similar acid-base-nucleophile catalytic mechanism. In our research, we are concerned with the structure that surrounds the key units of the catalytic machinery, and we have previously found conserved structural organizations that coordinate the catalytic acid, the catalytic nucleophile and the residues of the oxyanion hole. Here, we explore the architecture that surrounds the catalytic histidine at the active sites of enzymes from 40 ABH fold families, where we have identified six conserved interactions that coordinate the catalytic histidine next to the catalytic acid and the catalytic nucleophile. Specifically, the catalytic nucleophile is coordinated next to the catalytic histidine by two weak hydrogen bonds, while the catalytic acid is directly involved in the coordination of the catalytic histidine through by two weak hydrogen bonds. The imidazole ring of the catalytic histidine is coordinated by a CH-π contact and a hydrophobic interaction. Moreover, the catalytic triad residues are connected with a residue that is located at the core of the active site of ABH fold, which is suggested to be the fourth member of a “structural catalytic tetrad”. Besides their role in the stability of the catalytic mechanism, the conserved elements of the catalytic site are actively involved in ligand binding and affect other properties of the catalytic activity, such as substrate specificity, enantioselectivity, pH optimum and thermostability of ABH fold enzymes. These properties are regularly targeted in protein engineering applications, and thus, the identified conserved structural elements can serve as potential modification sites in order to develop ABH fold enzymes with altered activities.

Systematically Scrutinizing the Impact of Substitution Sites on Thermostability and Detergent Tolerance for Bacillus subtilis Lipase A

Improving an enzyme's (thermo-)stability or tolerance against solvents and detergents is highly relevant in protein engineering and biotechnology. Recent developments have tended toward data-driven approaches, where available knowledge about the protein is used to identify substitution sites with high potential to yield protein variants with improved stability, and subsequently, substitutions are engineered by site-directed or site-saturation (SSM) mutagenesis. However, the development and validation of algorithms for data-driven approaches have been hampered by the lack of availability of large-scale data measured in a uniform way and being unbiased with respect to substitution types and locations. Here, we extend our knowledge on guidelines for protein engineering following a data-driven approach by scrutinizing the impact of substitution sites on thermostability or/and detergent tolerance for Bacillus subtilis lipase A (BsLipA) at very large scale. We systematically analyze a complete experimental SSM library of BsLipA containing all 3439 possible single variants, which was evaluated as to thermostability and tolerances against four detergents under respectively uniform conditions. Our results provide systematic and unbiased reference data at unprecedented scale for a biotechnologically important protein, identify consistently defined hot spot types for evaluating the performance of data-driven protein-engineering approaches, and show that the rigidity theory and ensemble-based approach Constraint Network Analysis yields hot spot predictions with an up to ninefold gain in precision over random classification.

The Membrane-Integrated Steric Chaperone Lif Facilitates Active Site Opening of Pseudomonas aeruginosa Lipase A

Lipases are essential and widely used biocatalysts. Hence, the production of lipases requires a detailed understanding of the molecular mechanism of its folding and secretion. Lipase A from Pseudomonas aeruginosa, PaLipA, constitutes a prominent example that has additional relevance because of its role as a virulence factor in many diseases. PaLipA requires the assistance of a membrane-integrated steric chaperone, the lipase-specific foldase Lif, to achieve its enzymatically active state. However, the molecular mechanism of how Lif activates its cognate lipase has remained elusive. Here, we show by molecular dynamics simulations at the atomistic level and potential of mean force computations that Lif catalyzes the activation process of PaLipA by structurally stabilizing an intermediate PaLipA conformation, particularly a β-sheet in the region of residues 17-30, such that the opening of PaLipA's lid domain is facilitated. This opening allows substrate access to PaLipA's catalytic site. A surprising and so far not fully understood aspect of our study is that the open state of PaLipA is unstable compared to the closed one according to our computational and in vitro biochemical results. We thus speculate that further interactions of PaLipA with the Xcp secretion machinery and/or components of the extracellular matrix contribute to the remaining activity of secreted PaLipA. © 2019 Wiley Periodicals, Inc.

Thermostability of Lipase A and Dynamic Communication Based on Residue Interaction Network

OBJECTIVE

Dynamic communication caused by mutation affects protein stability. The main objective of this study is to explore how mutations affect communication and to provide further insight into the relationship between heat resistance and signal propagation of Bacillus subtilis lipase (Lip A).

METHODS

The relationship between dynamic communication and Lip A thermostability is studied by long-time MD simulation and residue interaction network. The Dijkstra algorithm is used to get the shortest path of each residue pair. Subsequently, time-series frequent paths and spatio-temporal frequent paths are mined through an Apriori-like algorithm.

RESULTS

Time-series frequent paths show that the communication between residue pairs, both in wild-type lipase (WTL) and mutant 6B, becomes chaotic with an increase in temperature; however, more residues in 6B can maintain stable communication at high temperature, which may be associated with the structural rigidity. Furthermore, spatio-temporal frequent paths reflect the interactions among secondary structures. For WTL at 300K, β7, αC, αB, the longest loop, αA and αF contact frequently. The 310-helix between β3 and αA is penetrated by spatio-temporal frequent paths. At 400K, only αC can be frequently transmitted. For 6B, when at 300K, αA and αF are in more tight contact by spatio-temporal frequent paths though I157M and N166Y. Moreover, the rigidity of the active site His156 and the C-terminal of Lip A are increased, as reflected by the spatio-temporal frequent paths. At 400K, αA and αF, 310-helix between β3 and αA, the longest loop, and the loop where the active site Asp133 is located can still maintain stable communication.

CONCLUSION

From the perspective of residue dynamic communication, it is obviously found that mutations cause changes in interactions between secondary structures and enhance the rigidity of the structure, contributing to the thermal stability and functional activity of 6B.

Changes of Thermostability, Organic Solvent, and pH Stability in Geobacillus zalihae HT1 and Its Mutant by Calcium Ion

Thermostable T1 lipase from Geobacillus zalihae has been crystallized using counter-diffusion method under space and Earth conditions. The comparison of the three-dimensional structures from both crystallized proteins show differences in the formation of hydrogen bond and ion interactions. Hydrogen bond and ion interaction are important in the stabilization of protein structure towards extreme temperature and organic solvents. In this study, the differences of hydrogen bond interactions at position Asp43, Thr118, Glu250, and Asn304 and ion interaction at position Glu226 was chosen to imitate space-grown crystal structure, and the impact of these combined interactions in T1 lipase-mutated structure was studied. Using space-grown T1 lipase structure as a reference, subsequent simultaneous mutation D43E, T118N, E226D, E250L, and N304E was performed on recombinant wild-type T1 lipase (wt-HT1) to generate a quintuple mutant term as 5M mutant lipase. This mutant lipase shared similar characteristics to its wild-type in terms of optimal pH and temperature. The stability of mutant 5M lipase improved significantly in acidic and alkaline pH as compared to wt-HT1. 5M lipase was highly stable in organic solvents such as dimethyl sulfoxide (DMSO), methanol, and n-hexane compared to wt-HT1. Both wild-type and mutant lipases were found highly activated in calcium as compared to other metal ions due to the presence of calcium-binding site for thermostability. The presence of calcium prolonged the half-life of mutant 5M and wt-HT1, and at the same time increased their melting temperature (T_m). The melting temperature of 5M and wt-HT1 lipases increased at 8.4 and 12.1 °C, respectively, in the presence of calcium as compared to those without. Calcium enhanced the stability of mutant 5M in 25% (v/v) DMSO, n-hexane, and n-heptane. The lipase activity of wt-HT1 also increased in 25% (v/v) ethanol, methanol, acetonitrile, n-hexane, and n-heptane in the presence of calcium. The current study showed that the accumulation of amino acid substitutions D43E, T118N, E226D, E250L, and N304E produced highly stable T1 mutant when hydrolyzing oil in selected organic solvents such as DMSO, n-hexane, and n-heptane. It is also believed that calcium ion plays important role in regulating lipase thermostability.

Filling the Void: Introducing Aromatic Interactions into Solvent Tunnels To Enhance Lipase Stability in Methanol

An enhanced stability of enzymes in organic solvents is desirable under industrial conditions. The potential of lipases as biocatalysts is mainly limited by their denaturation in polar alcohols. In this study, we focused on selected solvent tunnels in lipase from Geobacillus stearothermophilus T6 to improve its stability in methanol during biodiesel synthesis. Using rational mutagenesis, bulky aromatic residues were incorporated to occupy solvent channels and induce aromatic interactions leading to a better inner core packing. The chemical and structural characteristics of each solvent tunnel were systematically analyzed. Selected residues were replaced with Phe, Tyr, or Trp. Overall, 16 mutants were generated and screened in 60% methanol, from which 3 variants showed an enhanced stability up to 81-fold compared with that of the wild type. All stabilizing mutations were found in the longest tunnel detected in the "closed-lid" X-ray structure. The combination of Phe substitutions in an A187F/L360F double mutant resulted in an increase in unfolding temperature (T_m ) of 7°C in methanol and a 3-fold increase in biodiesel synthesis yield from waste chicken oil. A kinetic analysis with p-nitrophenyl laurate revealed that all mutants displayed lower hydrolysis rates (k _cat), though their stability properties mostly determined the transesterification capability. Seven crystal structures of different variants were solved, disclosing new π-π or CH/π intramolecular interactions and emphasizing the significance of aromatic interactions for improved solvent stability. This rational approach could be implemented for the stabilization of other enzymes in organic solvents.IMPORTANCE Enzymatic synthesis in organic solvents holds increasing industrial opportunities in many fields; however, one major obstacle is the limited stability of biocatalysts in such a denaturing environment. Aromatic interactions play a major role in protein folding and stability, and we were inspired by this to redesign enzyme voids. The rational protein engineering of solvent tunnels of lipase from Geobacillus stearothermophilus is presented here, offering a promising approach to introduce new aromatic interactions within the enzyme core. We discovered that longer tunnels leading from the surface to the enzyme active site were more beneficial targets for mutagenesis for improving lipase stability in methanol during biodiesel biosynthesis. A structural analysis of the variants confirmed the generation of new interactions involving aromatic residues. This work provides insights into stability-driven enzyme design by targeting the solvent channel void.

Kinematic Flexibility Analysis: Hydrogen Bonding Patterns Impart a Spatial Hierarchy of Protein Motion

Elastic network models (ENMs) and constraint-based, topological rigidity analysis are two distinct, coarse-grained approaches to study conformational flexibility of macromolecules. In the two decades since their introduction, both have contributed significantly to insights into protein molecular mechanisms and function. However, despite a shared purpose of these approaches, the topological nature of rigidity analysis, and thereby the absence of motion modes, has impeded a direct comparison. Here, we present an alternative, kinematic approach to rigidity analysis, which circumvents these drawbacks. We introduce a novel protein hydrogen bond network spectral decomposition, which provides an orthonormal basis for collective motions modulated by noncovalent interactions, analogous to the eigenspectrum of normal modes. The zero modes decompose proteins into rigid clusters identical to those from topological rigidity, while nonzero modes rank protein motions by their hydrogen bond collective energy penalty. Our kinematic flexibility analysis bridges topological rigidity theory and ENM, enabling a detailed analysis of motion modes obtained from both approaches. Analysis of a large, structurally diverse data set revealed that collectivity of protein motions, reported by the Shannon entropy, is significantly reduced for rigidity theory compared to normal mode approaches. Strikingly, kinematic flexibility analysis suggests that the hydrogen bonding network encodes a protein-fold specific, spatial hierarchy of motions, which goes nearly undetected in ENM. This hierarchy reveals distinct motion regimes that rationalize experimental and simulated protein stiffness variations. Kinematic motion modes highly correlate with reported crystallographic B factors and molecular dynamics simulations of adenylate kinase. A formal expression for changes in free energy derived from the spectral decomposition indicates that motions across nearly 40% of modes obey enthalpy-entropy compensation. Taken together, our results suggest that hydrogen bond networks have evolved to modulate protein structure and dynamics, which can be efficiently probed by kinematic flexibility analysis.

Ensemble-based modeling and rigidity decomposition of allosteric interaction networks and communication pathways in cyclin-dependent kinases: Differentiating kinase clients of the Hsp90-Cdc37 chaperone

The overarching goal of delineating molecular principles underlying differentiation of protein kinase clients and chaperone-based modulation of kinase activity is fundamental to understanding activity of many oncogenic kinases that require chaperoning of Hsp70 and Hsp90 systems to attain a functionally competent active form. Despite structural similarities and common activation mechanisms shared by cyclin-dependent kinase (CDK) proteins, members of this family can exhibit vastly different chaperone preferences. The molecular determinants underlying chaperone dependencies of protein kinases are not fully understood as structurally similar kinases may often elicit distinct regulatory responses to the chaperone. The regulatory divergences observed for members of CDK family are of particular interest as functional diversification among these kinases may be related to variations in chaperone dependencies and can be exploited in drug discovery of personalized therapeutic agents. In this work, we report the results of a computational investigation of several members of CDK family (CDK5, CDK6, CDK9) that represented a broad repertoire of chaperone dependencies—from nonclient CDK5, to weak client CDK6, and strong client CDK9. By using molecular simulations of multiple crystal structures we characterized conformational ensembles and collective dynamics of CDK proteins. We found that the elevated dynamics of CDK9 can trigger imbalances in cooperative collective motions and reduce stability of the active fold, thus creating a cascade of favorable conditions for chaperone intervention. The ensemble-based modeling of residue interaction networks and community analysis determined how differences in modularity of allosteric networks and topography of communication pathways can be linked with the client status of CDK proteins. This analysis unveiled depleted modularity of the allosteric network in CDK9 that alters distribution of communication pathways and leads to impaired signaling in the client kinase. According to our results, these network features may uniquely define chaperone dependencies of CDK clients. The perturbation response scanning and rigidity decomposition approaches identified regulatory hotspots that mediate differences in stability and cooperativity of allosteric interaction networks in the CDK structures. By combining these synergistic approaches, our study revealed dynamic and network signatures that can differentiate kinase clients and rationalize subtle divergences in the activation mechanisms of CDK family members. The therapeutic implications of these results are illustrated by identifying structural hotspots of pathogenic mutations that preferentially target regions of the increased flexibility to enable modulation of activation changes. Our study offers a network-based perspective on dynamic kinase mechanisms and drug design by unravelling relationships between protein kinase dynamics, allosteric communications and chaperone dependencies.

Contribution of single amino acid and codon substitutions to the production and secretion of a lipase by Bacillus subtilis

Background

Bacillus subtilis produces and secretes proteins in amounts of up to 20 g/l under optimal conditions. However, protein production can be challenging if transcription and cotranslational secretion are negatively affected, or the target protein is degraded by extracellular proteases. This study aims at elucidating the influence of a target protein on its own production by a systematic mutational analysis of the homologous B. subtilis model protein lipase A (LipA). We have covered the full natural diversity of single amino acid substitutions at 155 positions of LipA by site saturation mutagenesis excluding only highly conserved residues and qualitatively and quantitatively screened about 30,000 clones for extracellular LipA production. Identified variants with beneficial effects on production were sequenced and analyzed regarding B. subtilis growth behavior, extracellular lipase activity and amount as well as changes in lipase transcript levels.

Results

In total, 26 LipA variants were identified showing an up to twofold increase in either amount or activity of extracellular lipase. These variants harbor single amino acid or codon substitutions that did not substantially affect B. subtilis growth. Subsequent exemplary combination of beneficial single amino acid substitutions revealed an additive effect solely at the level of extracellular lipase amount; however, lipase amount and activity could not be increased simultaneously.

Conclusions

Single amino acid and codon substitutions can affect LipA secretion and production by B. subtilis. Several codon-related effects were observed that either enhance lipA transcription or promote a more efficient folding of LipA. Single amino acid substitutions could improve LipA production by increasing its secretion or stability in the culture supernatant. Our findings indicate that optimization of the expression system is not sufficient for efficient protein production in B. subtilis. The sequence of the target protein should also be considered as an optimization target for successful protein production. Our results further suggest that variants with improved properties might be identified much faster and easier if mutagenesis is prioritized towards elements that contribute to enzymatic activity or structural integrity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0772-z) contains supplementary material, which is available to authorized users.

Complex network analysis of thermostable mutants of Bacillus subtilis Lipase A

Three-dimensional structures of proteins that regulate their functions can be modelled using complex network based approaches for understanding the structure-function relationship. The six mutants of the protein Lipase A from Bacillus subtilis, harbouring 2 to 12 mutations, retain their function at higher temperatures with negligible variation in their overall three-dimensional crystallographic structures. This enhanced thermostability of the mutants questions the structure-function paradigm. In this paper, a coarse-grained complex network approach is used to elucidate the structural basis of enhanced thermostability in the mutant proteins, by uncovering small but significant local changes distributed throughout the structure, rendering stability to the mutants at higher temperatures. Community structure analysis of the six mutant protein networks uncovers the specific reorganisations among the nodes/residues that occur, in absence of overall structural variations, which induce enhanced rigidity underlying the increased thermostability. This study offers a novel and significant application of complex network analysis that proposes to be useful in the understanding and designing of thermostable proteins.