Molecular dynamics simulations investigate the pathway of substrate entry active site of rhomboid protease

Engineering the thermostability of d-lyxose isomerase from Caldanaerobius polysaccharolyticus via multiple computer-aided rational design for efficient synthesis of d-mannose

d-Mannose is an attractive functional sugar that exhibits many physiological benefits on human health. The demand for low-calorie sugars and sweeteners in foods are increasingly available on the market. Some sugar isomerases, such as d-lyxose isomerase (d-LIase), can achieve an isomerization reaction between d-mannose and d-fructose. However, the weak thermostability of d-LIase limits its efficient conversion from d-fructose to d-mannose. Nonetheless, few studies are available that have investigated the molecular modification of d-LIase to improve its thermal stability. In this study, computer-aided tools including FireProt, PROSS, and Consensus Finder were employed to jointly design d-LIase mutants with improved thermostability for the first time. Finally, the obtained five-point mutant M5 (N21G/E78P/V58Y/C119Y/K170P) showed high thermal stability and catalytic activity. The half-life of M5 at 65 °C was 10.22 fold, and the catalytic efficiency towards 600 g/L of d-fructose was 2.6 times to that of the wild type enzyme, respectively. Molecular dynamics simulation and intramolecular forces analysis revealed a thermostability mechanism of highly rigidity conformation, newly formed hydrogen bonds and π-cation interaction between and within protein domains, and redistributed surface electrostatic charges for the mutant M5. This research provided a promising d-LIase mutant for the industrial production of d-mannose from d-fructose.

Effect of Environmental Factors on the Catalytic Activity of Intramembrane Serine Protease

The cleavage of protein inside cell membranes regulates pathological pathways and is a subject of major interest. Thus, the nature of the coupling between the physical environment and the function of such proteins has recently attracted significant experimental and theoretical efforts. However, it is difficult to determine the nature of this coupling uniquely by experimental and theoretical studies unless one can separate the chemical and the environmental factors. This work describes calculations of the activation barriers of the intramembrane rhomboid protease in neutral and charged lipid bilayers and in detergent micelle, trying to explore the environmental effect. The calculations of the chemical barrier are done using the empirical valence bond (EVB) method. Additionally, the renormalization method captures the energetics and dynamical effects of the conformational change. The simulations indicate that the physical environment around the rhomboid protease is not a major factor in changing the chemical catalysis and that the conformational and substrate dynamics do not exhibit long-time coupling. General issues about the action of membrane-embedded enzymes are also considered.

Pulling Simulations and Hydrogen Sorption Modelling on Carbon Nanotube Bundles

Recent progress in molecular simulation technology has developed an interest in modernizing the usual computational methods and approaches. For instance, most of the theoretical work on hydrogen adsorption on carbon nanotubes was conducted a decade ago. It should be insightful to reinvestigate the field and take advantage of code improvements and features implemented in contemporary software. One example of such features is the pulling simulation modules now available in many molecular dynamics programs. We conduct pulling simulations on pairs of carbon nanotubes and measure the inter-tube distance before they dissociate in water. We use this distance to set the interval size between adjacent nanotubes as we arrange them in bundle configurations. We consider bundles with triangular, intermediate and honeycomb patterns, and armchair nanotubes with a chiral index from n = 5 to n = 10. Then, we simulate low pressure hydrogen adsorption isotherms at 77 K, using the grand canonical Monte Carlo method. The different bundle configurations adsorb great hydrogen amounts that may exceed 2% wt at ambient pressures. The computed hydrogen capacities are considered large for physisorption on carbon nanostructures and attributed to the ultra-microporous network and extraordinary high surface area of the configured models.

Studying effects of different protonation states of His11 and His102 in ribose-5-phosphate isomerase of Trypanosoma cruzi: an example of cooperative behavior

The Trypanosoma cruzi ribose-5-phosphate isomerase B (TcRpiB) is a crucial piece in the pentose phosphate pathway and thus is a potential drug target for treatment of Chagas' disease. TcRpiB residues, such as Cys69, Asp45, Glu149 and Pro47, have confirmed their roles in substrate recognition, catalytic reaction and binding site conformation. However, the joint performance of His11 and His102, in the D-ribose-5-phosphate (R5P) in the catalysis is not well understood. In this work, we probed the influence of different protonation states of His11 and His102 on the behavior of the ligand R5P using molecular dynamics simulations, network analysis and thermodynamic integration. Simulations revealed that a protonated His11 combined with a neutral His102 (His11⁺‒His102) was able to stabilize the ligand R5P in the binding site. Moreover, calculated relative free energy differences showed that when protonated His11 was coupled to a neutral His102 an exergonic process takes place. On the other hand, neutral His11 combined with a protonated His102 (His11‒His102⁺), sampled conformations that resembled the catalyzed product D-ribulose-5-phosphate (Ru5P). Network analysis also demonstrated some peculiarities for these systems with some negatively correlated nodes in the binding site for His11‒His102⁺, and exclusive suboptimal paths for His11⁺‒His102. Therefore, the combined approach presented in this paper proposes two suitable protonation states for the TcRpiB catalytic mechanism, where an extra proton in either histidines might favor R5P binding or influence isomerization reaction to Ru5P. Our results may guide further in silico drug discovery studies. Communicated by Ramaswamy H. Sarma.