Specificity in lipases: a computational study of transesterification of sucrose

Enzymatic Synthesis of Lipophilic Esters of Phenolic Compounds, Evaluation of Their Antioxidant Activity and Effect on the Oxidative Stability of Selected Oils

The aim of the study was to compare the effect of the substituent and its position in the aromatic ring on the antioxidant activity of hexanoic acid esters obtained in reactions catalyzed by immobilized lipase B from Candida antarctica. 4-Hydroxybenzyl hexanoate, 2-hydroxybenzyl hexanoate, 4-methoxybenzyl hexanoate, and vanillyl hexanoate were obtained with conversion yields of 50 to 80%. The antioxidant activity of synthesized esters, their alcohol precursors and BHT (Butylated HydroxyToluene) was compared with DPPH (2,2-diphenyl-1-picrylhydrazyl), CUPRAC (cupric ion reducing antioxidant capacity), and CBA (crocin bleaching assay) methods. Furthermore, it was investigated whether the presence of vanillyl hexanoate in a concentration of 0.01 and 0.1% affected the oxidative stability of sunflower and rapeseed oils in the Rancimat test. It was observed that the antioxidant activity of hexanoic acid esters depends on the presence and position of the hydroxyl group in the aromatic ring. The highest activities were found for vanillyl alcohol, vanillyl hexanoate, and BHT. The addition of the ester and BHT significantly extended the induction times of the tested oils, and these compounds exhibited similar activity. Vanillyl hexanoate increased the induction time from 4.49 to 5.28 h and from 2.73 to 3.12 h in the case of rapeseed and sunflower oils, respectively.

Algorithm-based coevolution network identification reveals key functional residues of the α/β hydrolase subfamilies

Covariant residues identified by computational algorithms have provided new insights into enzyme evolutionary routes. However, the reliability and accuracy of routine statistical coupling analysis (SCA) are unable to satisfy the needs of protein engineering because SCA depends only on sequence information. Here, we set up a new SCA algorithm, SCA.SIM, by integrating structure information and MD simulation data. The more reliable covariant residues with high-quality scores are obtained from sequence alignment weighted by residual movement for eight related subfamilies, belonging to α/β hydrolase family, with Candida antarctica lipase B (CALB). The 38 predicted covariant residues are tested for function by high-throughput quantitative evaluation in combination with activity and thermostability assays of a mutant library and deep sequencing. Based on the landscapes of both activity and thermostability, most mutants play key roles in catalysis, and some mutants gain 2.4- to 6-fold increase in half-life at 50°C and 9- to 12-fold improvement in catalytic efficiency. The activity of double mutants for A225F/T103A is higher than those of A225F and T103A which means that SCA.SIM method might be useful for identifying the allosteric coupling. The SCA.SIM algorithm can be used for protein coevolution and enzyme engineering research.

Factors determining the reaction temperature of the solvent-free enzymatic synthesis of trehalose esters

Solvent-free synthesis encourages the design of processes and products that reduce the use and generation of hazardous chemicals. Given the importance of developing greener methodologies, we sought to determine the factors influencing the reaction temperature required for solvent-free, enzymatic synthesis of sugar esters such as trehalose (TRE) esters, using Novozyme 435 as the enzyme catalyst. The use of lauric acid (La) and ethyl laurate (LaEt) as acyl donors did not affect the activation temperature for the generation of trehalose diesters (TDEs), despite the differences in corresponding by-products (water and ethanol). However, when glucose (GLU) and La were employed as reaction substrates as a comparison, glucose monoester (GME) generation readily occurred at much lower temperatures than with the TRE esters, even without a water collection device. Moreover, when the glass transition temperature (T_g) of the sugar substrates increased, a higher reaction temperature was required. These results suggest that while the activation temperature of the reaction did not correlate with the boiling point of the by-product, it did correlate with the glass transition temperature (T_g) of the trehalose substrates. Thus, our work demonstrates the importance of the physical state of amorphous matrices in determining the optimal reaction temperature of a solvent-free sugar synthesis.

The influence of the isocyanoesters structure on the course of enzymatic Ugi reactions

The impact of isocyanoesters structure on enzymatic three-component Ugi reactions course has been determined. The significant promiscuous ability of enzyme in Ugi-type reaction switching between four (U-4CR) and three (U-3CR) components reactions depending on the size of used isocyanoester. The application of short-chain cyanoesters up to isocyanpropionate leading to product of three component reaction exclusively while longer isocyanobutyrate gives only the product of four component reaction. The limitation of studied enzymatic Ugi reaction is a substrate selectivity of lipases.

Biosynthesis of Neokestose Laurate Catalyzed by Candida antarctica Lipase B and Its Antimicrobial Activity against Food Pathogenic and Spoilage Bacteria

To increase the functionality and broaden the potential application of neokestose, neokestose laurate was biosynthesized using Candida antarctica lipase B as biocatalyst, for which a mixture of 20% DMSO in 2-methyl-2-butanol (v/v) was chosen as the reaction medium. The optimum conditions for biosynthesis were as follows: a molar ratio of vinyl laurate to neokestose of 12, a temperature of 50 °C, molecular sieves of 100 g/L, and enzyme loading of 10 g/L. Under the optimal conditions, the conversion rate was achieved over 80%. The synthesized chemical 6'-O-lauroylneokestose confirmed by nuclear magnetic resonance (NMR) exhibited good emulsification with critical micelle concentration (CMC) of 352 μM and broad antibacterial activity against Gram-positive bacteria such as Staphylococcus aureus, Listeria monocytogenes, Streptococcus mutans, Bacillus subtilis, and Bacillus cereus. Conclusively, 6'-O-lauroylneokestose was evidenced to be a dual-functional agent with emulsification and antibacterial activity, showing promising application potential in the food industry.

Enzyme activity in liquid lipase melts as a step towards solvent-free biology at 150 °C

Water molecules play a number of critical roles in enzyme catalysis, including mass transfer of substrates and products, nucleophilicity and proton transfer at the active site, and solvent shell-mediated dynamics for accessing catalytically competent conformations. The pervasiveness of water in enzymolysis therefore raises the question concerning whether biocatalysis can be undertaken in the absence of a protein hydration shell. Lipase-mediated catalysis has been undertaken with reagent-based solvents and lyophilized powders, but there are no examples of molecularly dispersed enzymes that catalyse reactions at sub-solvation levels within solvent-free melts. Here we describe the synthesis, properties and enzyme activity of self-contained reactive biofluids based on solvent-free melts of lipase-polymer surfactant nanoconjugates. Desiccated substrates in liquid (p-nitrophenyl butyrate) or solid (p-nitrophenyl palmitate) form can be mixed or solubilized, respectively, into the enzyme biofluids, and hydrolysed in the solvent-free state. Significantly, the efficiency of product formation increases as the temperature is raised to 150 °C.

Enthalpie and Entropie Contributions in the Transesterification of Sucrose: Computational Study of Lipases and Subtilisin

Transesterification of sucrose with fatty acids catalyzed by subtilisin Carlsberg occurs with regioselectivity that is different from that in lipases. Thermomyces lanuginosus lipase (TlL) and Candida antarctica lipase B (CALB) catalyze synthesis at positions 6 and 6', with differing abilities, while subtilisin catalysis leads to the 1'-acylated sucrose. The catalytic machinery in lipases is approximately mirrored in subtilisins but different pocket morphologies including size, shape, and rearrangement of the catalytic elements underlies the differing regioselectivities. The thermodynamic consequences of these differences on the above reactions have been explored systematically using computational methods, determining the free energies of interaction of the putative transition-state adducts. Analysis of the conformers with the lowest transition state energies (protein-ligand interactions and vibrational entropy contributions) indicates that enthalpic factors control specificities in lipases while entropic factors are more important in subtilisin.

Structural basis of the sulphate starvation response in E. coli: crystal structure and mutational analysis of the cofactor-binding domain of the Cbl transcriptional regulator

Cbl is a member of the large family of LysR-type transcriptional regulators (LTTRs) common in bacteria and found also in Archaea and algal chloroplasts. The function of Cbl is required in Escherichia coli for expression of sulphate starvation-inducible (ssi) genes, associated with the biosynthesis of cysteine from organic sulphur sources (sulphonates). Here, we report the crystal structure of the cofactor-binding domain of Cbl (c-Cbl) from E. coli. The overall fold of c-Cbl is very similar to the regulatory domain (RD) of another LysR family member, CysB. The RD is composed of two subdomains enclosing a cavity, which is expected to bind effector molecules. We have constructed and analysed several full-length Cbl variants bearing single residue substitutions in the RD that affect cofactor responses. Using in vivo and in vitro transcription assays, we demonstrate that pssuE, a Cbl responsive promoter, is down-regulated not only by the cofactor, adenosine phosphosulphate (APS), but also by thiosulphate, and, that the same RD determinants are important for the response to both cofactors. We also demonstrate the effects of selected site-directed mutations on Cbl oligomerization and discuss these in the context of the structure. Based on the crystal structure and molecular modelling, we propose a model for the interaction of Cbl with adenosine phosphosulphate.