Structural Mechanism for the Temperature-Dependent Activation of the Hyperthermophilic Pf2001 Esterase

Dissecting the Effect of Temperature on Hyperthermophilic Pf2001 Esterase Dimerization by Molecular Dynamics

Pf2001 esterase (Pf2001) from Pyrococcus furiosus has hyperthermophilic properties and exerts a biocatalytic function in a dimeric state. Crystal structures revealed that the structural rearrangement of the cap domain is responsible for the Pf2001 dimer formation. However, the details of the cap domain remodeling and the effects of temperature on the dimerization process remain elusive at the molecular level, taking into account that experimental methods are difficult to capture the dynamic process of dimerization to some extent. Herein, four dimer models based on the monomeric crystal structure (PDB ID: 5G59) were constructed to investigate the conformational transition details and temperature effects in the dimerization by conventional molecular dynamics and accelerated molecular dynamics simulations. Our simulation results indicate that the monomer undergoes a conformational change into a "preparatory state" at high temperatures, which is more favorable for its transformation into a stable dimer. The subsequent free energy landscape analysis further identifies four intermediate states (from separated state to dimeric state) and discloses that a more accessible α-helix driven by stronger hydrophobic interactions induces a rearrangement of the cap domain, displaying a "tic-tac-toe" activation feature that is important for stabilizing the dimer interface and facilitating the formation of hydrophobic pockets. In addition, the electrostatic potential surface analysis illustrates that the weaker electrostatic repulsion (Lys and Arg) in the dimer interface at high temperatures is also a key factor for dimer stabilization. Altogether, our results can provide molecular-level insight into the dimer formation process of hyperthermophilic esterase and would be useful to understand the enzymatic specificity of α/β-hydrolase.

Crystal structures of herbicide-detoxifying esterase reveal a lid loop affecting substrate binding and activity

SulE, an esterase, which detoxifies a variety of sulfonylurea herbicides through de-esterification, provides an attractive approach to remove environmental sulfonylurea herbicides and develop herbicide-tolerant crops. Here, we determined the crystal structures of SulE and an activity improved mutant P44R. Structural analysis revealed that SulE is a dimer with spacious binding pocket accommodating the large sulfonylureas substrate. Particularly, SulE contains a protruding β hairpin with a lid loop covering the active site of the other subunit of the dimer. The lid loop participates in substrate recognition and binding. P44R mutation altered the lid loop flexibility, resulting in the sulfonylurea heterocyclic ring repositioning to a relative stable conformation thus leading to dramatically increased activity. Our work provides important insights into the molecular mechanism of SulE, and establish a solid foundation for further improving the enzyme activity to various sulfonylurea herbicides through rational design.

Role of N-Terminal Extensional Long α-Helix in the Arylesterase from Lacticaseibacillus rhamnosus GG on Catalysis and Stability

In the α/β hydrolases superfamily, the extra module modulated enzymatic activity, substrate specificity, and stability. The functional role of N-terminal extensional long α-helix (Ala2-Glu29, designated as NEL-helix) acting as the extra module in the arylesterase LggEst from Lacticaseibacillus rhamnosus GG had been systemically investigated by deletion mutagenesis, biochemical characterization, and biophysical methods. The deletion of the NEL-helix did not change the overall structure of this arylesterase. The deletion of the NEL-helix led to the shifting of optimal pH into the acidity and the loss of thermophilic activity. The deletion of the NEL-helix produced a 10.6-fold drop in catalytic activity towards the best substrate pNPC10. NEL-Helix was crucial for the thermostability, chemical resistance, and organic solvents tolerance. The deletion of the NEL-helix did not change the overall rigidity of enzyme structure and only reduced the local rigidity of the active site. Sodium deoxycholate might partially replenish the loss of activity caused by the deletion of the NEL-helix. Our research further enriched the functional role of the extra module on catalysis and stability in the α/β hydrolase fold superfamily.

Using Intrinsic Fluorescence to Measure Protein Stability Upon Thermal and Chemical Denaturation

Understanding how point mutations affect the performance of protein stability has been the focus of several studies all over the years. Intrinsic fluorescence is commonly used to follow protein unfolding since during denaturation, progressive redshifts on tryptophan fluorescence emission are observed. Since the unfolding process (achieved by chemical or physical denaturants) can be considered as two-state N➔D, it is possible to utilize the midpoint unfolding curves (fU = 50%) as a parameter to evaluate if the mutation destabilizes wild-type protein. The idea is to determine the [D]_1/2 or T_m values from both wild type and mutant and calculate the difference between them. Positive values indicate the mutant is less stable than wild type.

Toward the Complete Functional Characterization of a Minimal Bacterial Proteome

Recently, we presented a whole-cell kinetic model of the genetically minimal bacterium JCVI-syn3A that described the coupled metabolic and genetic information processes and predicted behaviors emerging from the interactions among these networks. JCVI-syn3A is a genetically reduced bacterial cell that has the fewest number and smallest fraction of genes of unclear function, with approximately 90 of its 452 protein-coding genes (that is less than 20%) unannotated. Further characterization of unclear JCVI-syn3A genes strengthens the robustness and predictive power of cell modeling efforts and can lead to a deeper understanding of biophysical processes and pathways at the cell scale. Here, we apply computational analyses to elucidate the functions of the products of several essential but previously uncharacterized genes involved in integral cellular processes, particularly those directly affecting cell growth, division, and morphology. We also suggest directed wet-lab experiments informed by our analyses to further understand these "missing puzzle pieces" that are an essential part of the mosaic of biological interactions present in JCVI-syn3A. Our workflow leverages evolutionary sequence analysis, protein structure prediction, interactomics, and genome architecture to determine upgraded annotations. Additionally, we apply the structure prediction analysis component of our work to all 452 protein coding genes in JCVI-syn3A to expedite future functional annotation studies as well as the inverse mapping of the cell state to more physical models requiring all-atom or coarse-grained representations for all JCVI-syn3A proteins.

Discovery of a New Microbial Origin Cold-Active Neopullulanase Capable for Effective Conversion of Pullulan to Panose

Panose is a type of functional sugar with diverse bioactivities. The enzymatic conversion bioprocess to produce high purity panose with high efficiency has become increasingly important. Here, a new neopullulanase (NPase), Amy117 from B. pseudofirmus 703, was identified and characterized. Amy117 presented the optimal activity at pH 7.0 and 30 °C, its activity is over 40% at 10 °C and over 80% at 20 °C, which is cold-active. The enzyme cleaved α-1, 4-glycosidic linkages of pullulan to generate panose as the only hydrolysis product, and degraded cyclodextrins (CDs) and starch to glucose and maltose, with an apparent preference for CDs. Furthermore, Amy117 can produce 72.7 mg/mL panose with a conversion yield of 91% (w/w) based on 80 mg/mL pullulan. The sequence and structure analysis showed that the low proportion of Arg, high proportion of Asn and Gln, and high α-helix levels in Amy117 may contribute to its cold-active properties. Root mean square deviation (RMSD) analysis also showed that Amy117 is more flexible than two mesophilic homologues. Hence, we discovered a new high-efficiency panose-producing NPase, which so far achieves the highest panose production and would be an ideal candidate in the food industry.

Structure and Dynamics of an Archeal Monoglyceride Lipase from Palaeococcus ferrophilus as Revealed by Crystallography and In Silico Analysis

The crystallographic analysis of a lipase from Palaeococcus ferrophilus (PFL) previously annotated as a lysophospholipase revealed high structural conservation with other monoglyceride lipases, in particular in the lid domain and substrate binding pockets. In agreement with this observation, PFL was shown to be active on various monoacylglycerols. Molecular Dynamics (MD) studies performed in the absence and in the presence of ligands further allowed characterization of the dynamics of this system and led to a systematic closure of the lid compared to the crystal structure. However, the presence of ligands in the acyl-binding pocket stabilizes intermediate conformations compared to the crystal and totally closed structures. Several lid-stabilizing or closure elements were highlighted, i.e., hydrogen bonds between Ser117 and Ile204 or Asn142 and its facing amino acid lid residues, as well as Phe123. Thus, based on this complementary crystallographic and MD approach, we suggest that the crystal structure reported herein represents an open conformation, at least partially, of the PFL, which is likely stabilized by the ligand, and it brings to light several key structural features prone to participate in the closure of the lid.

Unexplored lipolytic activity of Escherichia coli: Implications for lipase cloning

Recent investigations on cloned bacterial lipases performed in our laboratory revealed the presence of lipolytic activity that was not due to the cloned lipase-coding gene but was probably the result of an intrinsic activity of Escherichia coli itself. To confirm such a hypothesis, we assayed the activity of frequently used E. coli strains by fast paper tests, zymograms and spectrofluorometry. A band of Ca. 18-20 kDa showing activity on MUF-butyrate was detected in zymogram analysis of crude cell extracts in all E. coli strains assayed. Moreover, the spectrofluorometric results obtained confirmed the presence of low but significant lipolytic activity in E. coli, with strain BL21 showing the highest activity. Detailed characterization of such a lipolytic activity was performed using E. coli BL21 cell extracts, where preference for C7 substrates was found, although shorter substrates were also hydrolysed to a minor extent. Interestingly, E. coli lipolytic activity displays traits of a thermophilic enzyme, showing maximum activity at 50 °C and pH 8, an unexpected feature never described before. Kinetic and inhibition analysis were also performed showing that activity can be inhibited by several metal ions or by Triton X-100® and SDS, used in zymogram analysis. Such properties ‒ low activity, preference for medium chain-length substrates, and high operational temperature ‒ might justify why this activity had gone unexplored until now, even when many lipases and esterases have been cloned and expressed in E. coli strains in the past. From now on, lipase researchers should take into consideration the presence of such a basal lipolytic activity before starting their lipase cloning or expression experiments in E.coli.

Accelerated CO₂ Hydration with Thermostable Sulfurihydrogenibium azorense Carbonic Anhydrase-Chitin Binding Domain Fusion Protein Immobilised on Chitin Support

Carbonic anhydrases (CAs) represent a group of enzymes that catalyse important reactions of carbon dioxide hydration and dehydration, a reaction crucial to many biological processes and environmental biotechnology. In this study we successfully constructed a thermostable fusion enzyme composed of the Sulfurihydrogenibium azorense carbonic anhydrase (Saz_CA), the fastest CA discovered to date, and the chitin binding domain (ChBD) of chitinase from Bacillus circulans. Introduction of ChBD to the Saz_CA had no major impact on the effect of ions or inhibitors on the enzymatic activity. The fusion protein exhibited no negative effects up to 60 °C, whilst the fusion partner appears to protect the enzyme from negative effects of magnesium. The prepared biocatalyst appears to be thermally activated at 60 °C and could be partially purified with heat treatment. Immobilisation attempts on different kinds of chitin-based support results have shown that the fusion enzyme preferentially binds to a cheap, untreated chitin with a large crystallinity index over more processed forms of chitin. It suggests significant potential economic benefits for large-scale deployment of immobilised CA technologies such as CO₂ utilisation or mineralisation.

Contribution of the Oligomeric State to the Thermostability of Isoenzyme 3 from Candida rugosa

Thermophilic proteins have evolved different strategies to maintain structure and function at high temperatures; they have large, hydrophobic cores, and feature increased electrostatic interactions, with disulfide bonds, salt-bridging, and surface charges. Oligomerization is also recognized as a mechanism for protein stabilization to confer a thermophilic adaptation. Mesophilic proteins are less thermostable than their thermophilic homologs, but oligomerization plays an important role in biological processes on a wide variety of mesophilic enzymes, including thermostabilization. The mesophilic yeast Candida rugosa contains a complex family of highly related lipase isoenzymes. Lip3 has been purified and characterized in two oligomeric states, monomer (mLip3) and dimer (dLip3), and crystallized in a dimeric conformation, providing a perfect model for studying the effects of homodimerization on mesophilic enzymes. We studied kinetics and stability at different pHs and temperatures, using the response surface methodology to compare both forms. At the kinetic level, homodimerization expanded Lip3 specificity (serving as a better catalyst on soluble substrates). Indeed, dimerization increased its thermostability by more than 15 °C (maximum temperature for dLip3 was out of the experimental range; >50 °C), and increased the pH stability by nearly one pH unit, demonstrating that oligomerization is a viable strategy for the stabilization of mesophilic enzymes.