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E. coli thioesterase 'TesA is an important enzyme in fatty acid production. Medium-chain fatty acids (MCFAs, C6-C10) are of great interest due to their similar physicochemical properties to petroleum-based oleo-chemicals. It has been shown that wild-type 'TesA had better selectivity for long-chain acyl substrates (≥C16), while the two mutants 'TesAE142D/Y145G and 'TesAM141L/E142D/Y145G had better selectivity for medium-chain acyl substrates. However, it is difficult to obtain the selectivity mechanism of substrates for proteins by traditional experimental methods. In this study, in order to obtain more MCFAs, we analyzed the binding mode of proteins ('TesA, 'TesAE142D/Y145G and 'TesAM141L/E142D/Y145G) and substrates (C16/C8-N-acetylcysteamine analogs, C16/C8-SNAC), the key residues and catalytic mechanisms through molecular docking, molecular dynamics simulations and the molecular mechanics Poisson–Boltzmann surface area (MM/PBSA). The results showed that several main residues related to catalysis, including Ser10, Asn73 and His157, had a strong hydrogen bond interaction with the substrates. The mutant region (Met141-Tyr146) and loop107–113 were mainly dominated by Van der Waals contributions to the substrates. For C16-SNAC, except for 'TesAM141L/E142D/Y145G with large conformational changes, there were strong interactions at both head and tail ends that distorted the substrate into a more favorable high-energy conformation for the catalytic reaction. For C8-SNAC, the head and tail found it difficult to bind to the enzyme at the same time due to insufficient chain length, which made the substrate binding sites more variable, so 'TesAM141L/E142D/Y145G with better binding sites had the strongest activity, and 'TesA had the weakest activity, conversely. In short, the matching substrate chain and binding pocket length are the key factors affecting selectivity. This will be helpful for the further improvement of thioesterases. [ABSTRACT FROM AUTHOR]

• PVAc could be dissolved in CO 2 when the pressure was much higher than 30 MPa. • Cosolvents could decrease the transition points of PVAc in CO 2. • The mixtures of CO 2 and cosolvents have the solubility parameters close to PVAc. • The LA-LB interactions are the main influence factor of PVAc dissolving in CO 2. • The generated new interactions by cosolvents have great influence. The dissolution behavior of polymers in CO 2 has become increasingly important to the applications of CO 2 in industry. Experimental results showed that PVAc could be dissolved in CO 2 at a high pressure. When cosolvents such as ethanol, acetic acid, and ethyl acetate were present in the system, the transition points could be decreased with the increase in cosolvent concentration. In this work, the influence mechanisms of cosolvents on dissolution behaviors of PVAc in supercritical CO 2 were investigated by molecular dynamics simulation methods. First, the cohesive energy and solubility parameters of PVAc, cosolvents and CO 2 were analyzed. Compared with CO 2 , the mixtures of CO 2 and cosolvents have closer solubility parameters with PVAc to enhance the dissolubility of PVAc within them. Moreover, the mechanism of PVAc dissolution in CO 2 and the effects of cosolvents on decreasing the transition points were investigated. The Lewis acid–Lewis base (LA-LB) interactions between O atoms in PVAc and C atoms in CO 2 are the main influencing factors of PVAc dissolution in CO 2. The presence of cosolvent can generate new interactions, such as hydrogen bonding and LA-LB interactions, which have different influences on the LA-LB interactions between PVAc and CO 2. Ethanol and ethyl acetate have no great influence on these LA-LB interactions, while acetic acid exerts considerable influence. [ABSTRACT FROM AUTHOR]

The overexpression of p21-activated kinase 4 (PAK4) is associated with a variety of cancers. In this paper, the binding modes and inhibitory mechanisms of four 7H-pyrrolo[2,3-d]pyrimidine competitive inhibitors of PAK4 were investigated at the molecular level, mainly using molecular dynamics simulations and binding free energy calculations. The results show that the inhibitors had strong interactions with the hinge region, the β-sheets, and the residues with charged side chains around the 4-substituent. The terminal amino group of the inhibitor 5n was different from the other three, which could cause the enhancement of hydrogen bonds or electrostatic interactions formed with the surrounding residues. Thus, inhibitor 5n had the strongest inhibition capacity. The different halogen atoms on the 2-substituents of the inhibitors 5h, 5g, and 5e caused differences in the positions of the 2-benzene rings and affected the interactions of the hinge region. It also affected to some extent the orientations of the 4-imino groups and consequently their affinities for the surrounding charged residues. The combined results lead to the weakest inhibitory capacity of inhibitor 5e. [ABSTRACT FROM AUTHOR]