Conformational Dynamics in Corynebacterium glutamicum Diaminopimelate Epimerase: Insights from Ligand Parameterization, Atomistic Simulation, and Markov State Modeling.

The microbial enzyme diaminopimelate epimerase (DapF), a vital enzyme in the lysine biosynthetic pathway, catalyzes the conversion of L, L-diaminopimelate (L, L-DAP) to D, L-diaminopimelate (D, L-DAP) using a catalytic cysteine dyad with one cysteine in thiol state and another in thiolate. Under oxidizing conditions, the catalytic cysteines of apo DapF form a disulfide bond that alters the structure and function of DapF. Given its potential as a target for antimicrobial resistance treatments, understanding DapF's functional dynamics is imperative. In the present work, we employ microsecond-scale all-atom molecular dynamics simulations of product-bound DapF and apo-DapF under oxidized and reduced conditions. We employ a polarized charge model for the ligand and the active site residues, which was necessary to preserve the electrostatic environment in the active site and retain the ligand in the active site. The product-bound DapF and apo-DapF in oxidized and reduced conditions exhibit a closed, semi-open, and open conformation, respectively, as identified using the internal coordinates of the dimeric enzyme and the principal component analysis. The conformational switch is guided by the dynamic catalytic (DC) loop, loop II, and loop III movements in the active site. The time scale of the close-to-open conformational transition is estimated to be 0.8 µs through Markov state modeling (MSM) and transition path theory (TPT). The present study explains the role of various active site residues and loops in ligand binding and protein dynamics in the DapF enzyme under different redox conditions. Such information will be helpful in future inhibitor design studies targeting the DapF enzyme.

Energy Storage Application of Conducting Polymers Featuring Dual Acceptors: Exploring Conjugation and Flexible Chain Length Effects.

Solution-processable conducting polymers (CPs) are a compelling alternative to inorganic counterparts because of their potential for tuning chemical properties and creating flexible organic electronics. CPs, which typically comprise either only an electron donor (D) or its alternative combinations with an electron acceptor (A), exhibit charge transfer behavior between the units, resulting in an electrical conductivity suitable for utilization in electronic devices and for energy storage applications. However, the energy storage behavior of CPs with a sequence of electron acceptors (A-A), has rarely been investigated, despite their promising lower band gap and higher charge carrier mobility. Utilizing the aforesaid concept herein, four CPs featuring benzodithiophenedione (BDD), and diketopyrrolepyrrole (DPP) are synthesized. Among them, the BDDTH-DPPEH polymer exhibited the highest specific capacitance of 126.5 F g-1 at a current density of 0.5 A g-1 in an organic electrolyte over a wide potential window of -0.6-1.4 V. Notably, the supercapacitor properties of the polymeric electrode materials improved with increasing conjugation length by adding thiophene donor units and shortening the alkyl chain lengths. Furthermore, a symmetric supercapacitor device fabricated using BDDTH-DPPEH exhibited a high-power density of 4000 W kg-1 and an energy density of 31.66 Wh kg-1 .

The coordinated action of the enzymes in the L-lysine biosynthetic pathway and how to inhibit it for antibiotic targets.

BACKGROUND: Antimicrobial resistance is a global health issue that requires immediate attention in terms of new antibiotics and new antibiotic targets. The l-lysine biosynthesis pathway (LBP) is a promising avenue for drug discovery as it is essential for bacterial growth and survival and is not required by human beings. SCOPE OF REVIEW: The LBP involves a coordinated action of fourteen different enzymes distributed over four distinct sub-pathways. The enzymes involved in this pathway belong to different classes, such as aspartokinase, dehydrogenase, aminotransferase, epimerase, etc. This review provides a comprehensive account of the secondary and tertiary structure, conformational dynamics, active site architecture, mechanism of catalytic action, and inhibitors of all enzymes involved in LBP of different bacterial species. MAJOR CONCLUSIONS: LBP offers a wide scope for novel antibiotic targets. The enzymology of a majority of the LBP enzymes is well understood, although these enzymes are less widely studied in the critical pathogens (according to the 2017 WHO report) that require immediate attention. In particular, the enzymes in the acetylase pathway, DapAT, DapDH, and Aspartokinase in critical pathogens have received little attention. High throughput screening for inhibitor design against the enzymes of lysine biosynthetic pathway is rather limited, both in number and in the extent of success. GENERAL SIGNIFICANCE: This review can serve as a guide for the enzymology of LBP and help in identifying new drug targets and designing potential inhibitors.

Ligands-induced open-close conformational change during DapE catalysis: Insights from molecular dynamics simulations.

The microbial enzyme DapE plays a critical role in the lysine biosynthetic pathway and is considered as a potentially safe antibiotic target. In this study, atomistic simulations are employed to identify the modes of essential dynamics that define the conformational response of the enzyme to ligand binding and unbinding. The binding modes and the binding affinities of the products to the DapE enzyme are estimated from the MM-PBSA method, and the residues contributing to the ligand binding are identified. Various structural analyses and the principal component analysis of the molecular dynamics trajectories reveal that the removal of products from the active site causes a significant change in the overall enzyme structure. Both Cartesian and dihedral principal component analyses are used to characterize the structural changes in terms of domain unfolding and domain twisting motions. In the most dominant mode, that is, the domain unfolding motion, the two catalytic domains move away from the two dimerization domains of the dimeric enzyme, representing a closed-to-open conformational change. The conformational changes are initiated by the coordinated movement of three loops (Asp75-Pro82, Gly240-Asn244, and Thr347-Glu353) that trigger a domain-level movement. From multiple short trajectories, the time constant associated with the domain opening motion is estimated as 43.6 ns. Physiologically, this close-to-open conformational change is essential for the regeneration of the initial state of the enzyme for the subsequent cycle of catalytic action and provides the apo enzyme enough flexibility for efficient substrate binding.

Pomegranate peel polyphenols prophylaxis against SARS-CoV-2 main protease by in-silico docking and molecular dynamics study.

Pomegranate peel, the waste product generated from pomegranate fruit, has prophylactic properties, such as antimicrobial, anti-malarial, and controls respiratory infections and influenza. Based on the previous literature and need of the hour, molecular docking was performed to evaluate the inhibitory effects of major pomegranate peel polyphenols against COVID-19. Among the 44 studied compounds, 37 polyphenols show interaction with the catalytic dyad of the Mpro protease and 18 polyphenols have a higher binding affinity than that of the Mpro protease inhibitor (N3), indicating their high probability of binding at ACE2: SARS-CoV-2 interface. Furthermore, several polyphenols studied in this work are found to have higher binding affinity as compared to those of hydroxychloroquine, lopinavir, nelfinavir, and curcumin, some of which have been earlier tested against COVID-19. Further, molecular dynamics simulations (200 ns) for Mpro-polyphenols including pelargonidin3-glucoside, quercetin3-O-rhamnoside, cyanidin3-glucoside and punicalin revealed highly stable complexes with less conformational fluctuations and similar degree of compactness. Estimation of total number of intermolecular hydrogen bonds and binding free energy confirmed the stability of these Mpro-polyphenol complexes over Mpro-curcumin complex. Based on the greater binding affinity of polyphenols of pomegranate peel towards Mpro as compared to that of curcumin, pomegranate peel may be considered in any herbal medicinal formulation or may be incorporated into daily diets for prevention of COVID-19.Communicated by Ramaswamy H. Sarma.