QM/MM and MM MD simulations on decontamination of the V-type nerve agent VX by phosphotriesterase: Toward a comprehensive understanding of steroselectivity and activity

Due to deadly toxicity and high environmental stability of the nerve agent VX, an efficient decontamination approach is desperately needed in tackling its severe threat to human secu-rity. The enzymatic...

Atomic-Level Investigation of Reactant Recognition Mechanism and Thermodynamic Property in Glucosamine 6-Phosphate Deaminase Catalysis

Glucosamine 6-phosphate deaminase (NagB) influences the direction of N-acetylglucosamine (GlcNAc) metabolism, facilitating the conversion of D-glucosamine 6-phosphate (GlcN6P) to D-fructose 6-phosphate (Fru6P) with the release of ammonia. Here, extensive molecular dynamics simulations combined with various techniques were performed to study the recognition and delivery process of GlcN6P by SmuNagB, due to its guidance of subsequent enzymatic reaction. The key residues Lys194, His130, Arg127, Thr38, and Ser37 stabilize GlcN6P in the active site by hydrogen bond interactions, therein electrostatic and polar solvent effects provide the primary traction. Four delivery channels were identified, with GlcN6P most likely to enter the active site of NagB through a “door” comprising residues 6–10, 122–136, and 222–233. The corresponding mechanism and thermodynamic properties were investigated. An exothermic recognition and delivery process were detected, accompanied by the flipping of GlcN6P and changes in key direct and indirect hydrogen bond interactions, which provide the driving force for the chemical reaction to occur. Furthermore, “the lid motif” was identified that remain open in alkaline condition with different extent of opening at each stage of transfer that induced GlcN6P to move the active site of NagB. The work will assist in the elucidation of the catalytic mechanism of action of NagB, allowing inhibitors to be designed with superior dynamic behavior.

Insight into the delivery channel and selectivity of multiple binding sites in bovine serum albumin towards naphthalimide-polyamine derivatives

Naphthalimide derivatives are types of small-molecule anticancer drug candidates; however, their negative factors and potential side effects make their application limited. The pharmacophores select a direct access into the tumor cells as the first choice; this can reduce the side effect of the anti-cancer drugs on the normal cells. Herein, the delivery and binding of the naphthalimide-polyamine complex assisted by the bovine serum albumin (BSA) protein have been studied by combining several molecular dynamic simulations. The plausible transportation channels and the most favorable pathways for the delivery of the naphthalimide-polyamine complex to two drug sites (DSI and DSII), their thermodynamic and dynamic properties and the mechanisms have been discussed in detail. The residues His287 and Phe394 acted as guards in the DSI and DSII, respectively, which played a gating-switch role by flipping the ring from open to close during the compound delivery. The binding mode, binding energy and substituent effects have been also identified. The two drug sites have different preferences towards the compound with the electron-withdrawing and electron-donating substituents, and their strong interactions are more sensitive to the number of the substituent groups. The naphthalimide-polyamine complexes are more likely to choose DSI, both thermodynamically and dynamically, as compared to DSII. This selective specificity of these two drug sites manipulated by the electron-withdrawing and electron-donating substituents is quite promising for the design of new naphthalimide drugs.

Mechanistic insights into the catalytic reaction of ferulic acid decarboxylase from Aspergillus niger: a QM/MM study

Ubiquinone plays a pivotal role in the aerobic cellular respiratory electron transport chain, whereas ferulic acid decarboxylase (FDC) is involved in the biosynthesis of ubiquinone precursor. Recently, the complete crystal structure of FDC (based on the co-expression of the A. niger fdc1 gene in E. coli with the associated ubix gene from E. coli) at high resolution was reported. Herein, the detailed catalytic non-oxidative decarboxylation mechanism of FDC has been investigated by a combined quantum mechanics/molecular mechanics (QM/MM) approach. Calculation results indicate that, after the 1,3-dipolar cycloaddition of the substrate and cofactor, the carboxylic group can readily split off from the adduct, and the overall energy barrier of the whole catalytic reaction is 23.5 kcal mol^-1. According to the energy barrier analysis, the protonation step is rate-limiting. The conserved protonated Glu282 is suggested to be the proton donor through a "water bridge". Besides, two cases, that is, the generated CO₂ escapes from the active site or remains in the active site, were considered. It was found that the prolonged leaving of CO₂ can facilitate the protonation of the intermediate. In particular, our calculations shed light on the detailed function of both cofactors prFMN^iminium and prFMN^ketamine in the decarboxylation step. The cofactor prFMN^iminium is the catalytically relevant species compared with prFMN^ketamine.

QM/MM and MM MD Simulations on the Pyrimidine-Specific Nucleoside Hydrolase: A Comprehensive Understanding of Enzymatic Hydrolysis of Uridine

The pyrimidine-specific nucleoside hydrolase Yeik (CU-NH) from Escherichia coli cleaves the N-glycosidic bond of uridine and cytidine with a 10²-10⁴-fold faster rate than that of purine nucleoside substrates, such as inosine. Such a remarkable substrate specificity and the plausible hydrolytic mechanisms of uridine have been explored by using QM/MM and MM MD simulations. The present calculations show that the relatively stronger hydrogen-bond interactions between uridine and the active-site residues Gln227 and Tyr231 in CU-NH play an important role in enhancing the substrate binding and thus promoting the N-glycosidic bond cleavage, in comparison with inosine. The estimated energy barrier of 30 kcal/mol for the hydrolysis of inosine is much higher than 22 kcal/mol for uridine. Extensive MM MD simulations on the transportation of substrates to the active site of CU-NH indicate that the uridine binding is exothermic by ∼23 kcal/mol, more remarkable than inosine (∼12 kcal/mol). All of these arise from the noncovalent interactions between the substrate and the active site featured in CU-NH, which account for the substrate specificity. Quite differing from other nucleoside hydrolases, here the enzymatic N-glycosidic bond cleavage of uridine is less influenced by its protonation.

Mechanisms for the deamination reaction of 8-oxoguanine catalyzed by 8-oxoguanine deaminase: A combined QM/MM molecular dynamics study

The deamination reaction of 8-oxoguanine (8-oxoG) catalyzed by 8-oxoguanine deaminase (8-oxoGD) plays a critically important role in the DNA repair activity for oxidative damage. In order to elucidate the complete enzymatic catalysis mechanism at the stages of 8-oxoguanine binding, departure of 2-hydroxy-1H-purine-6,8(7H,9H)-dione from the active site, and formation of 8-oxoxanthine, extensive combined QM(PM3)/MM molecular dynamics simulations have been performed. Computations show that the rate-limiting step corresponds to the nucleophilic attack from zinc-coordinate hydroxide group to free 8-oxoguanine. Through conformational analyses, we demonstrate that Trp115, Trp123 and Leu119 connect to O8@8-oxoguanine with hydrogen bonds, and we suggest that mutations of tryptophan (115 and 123) to histidine or phenylalanine and mutation of leucine (119) to alanine could potentially lead to a mutant with enhanced activity. On this ground, a proton transfer mechanism for the formation of 8-oxoxanthine was further discussed. Both Glu218 and water molecule could be used as proton shuttles, and water molecule plays a major role in proton transfer in substrate. On the other hand, comparative simulations on the deamination of guanine and isocytosine reveal that, for the helping of hydrogen bonds between O8@8-oxoguanine and enzyme, O8@8-oxoguanine is the fastest to be deaminated among the three substrates which are also supported by the experimental kinetic constants.

Proton transfer rates in ionized water clusters (H2O)n (n = 2–4)

A proton transfer process is usually dominant in several biological phenomena such as the energy relaxation of photo-excited DNA base pairs and a charge relay process in Ser-His-Glu.