CD-sensitive Zn-porphyrin tweezer host-guest complexes, part 1: MC/OPLS-2005 computational approach for predicting preferred interporphyrin helicity

Insight into novel inhibitors from Sterculia urens against Cholera via pharmacoinformatics and molecular dynamics simulation approaches

The underdeveloped countries with large populations are facing a grave global threat in the form of cholera. Vibrio cholerae, the etiologic agent of Cholera has drawn attention recently due to antimicrobial resistance and resulting outbreaks that necessitates establishment of novel medications to counteract virulence and viability of the pathogen. Sterculia urens Roxb. (Malvaceae) is an ethnomedicinally important tree, which harbors a good number of bioactive phytocompounds. In the present study, 53 phytocompounds of S. urens were screened against the promising target ToxT of V. cholerae employing structure-based drug design approach that revealed three lead compounds, viz., 4,4,5,8-Tetramethylchroman-2-ol (-8.2 kcal/mol), Beta-Bisabolol (-8.2 kcal/mol) and Ledol (-8.7 kcal/mol) with satisfactory ADMET properties. Molecular dynamics simulation for 150 ns unveiled notable compactness and structural stability for the lead compounds considering RMSD, RMSF, Rg, MolSA, PSA and protein-ligand contacts parameters. Molecular mechanics-based MM/GBSA binding energy calculation revealed Beta-Bisabolol (-66.74 kcal/mol) to have better scores than 4,4,5,8-Tetramethylchroman-2-ol (-47.42 kcal/mol) and Ledol (-65.79 kcal/mol). Enzymes were mostly found as drug target class, and Nabilone was found as a structurally similar analog for 4,4,5,8-Tetramethylchroman-2-ol. These discoveries could aid in revealing new antibacterial medications targeting ToxT to combat Cholera.Communicated by Ramaswamy H. Sarma.

Validation of crystal structure of 2-acetamidophenyl acetate: an experimental and theoretical study

In this present study, we have determined the crystal structure of 2-acetamidophenyl acetate (2-AAPA) commonly used as influenza neuraminidase inhibitor, to analyze the polymorphism. Molecular docking and molecular dynamics have been performed for the 2-AAPA-neuraminidase complex as the ester-derived benzoic group shows several biological properties. The X-ray diffraction studies confirmed that the 2-AAPA crystals are stabilized by N-H···O type of intermolecular interactions. Possible conformers of 2-AAPA crystal structures were computationally predicted by ab initio methods and the stable crystal structure was identified. Hirshfeld surface analysis of both experimental and predicted crystal structure exhibits the intermolecular interactions associated with 2D fingerprint plots. The lowest docking score and intermolecular interactions of 2-AAPA molecule against influenza neuraminidase confirm the binding affinity of the 2-AAPA crystals. The quantum theory of atoms in molecules analysis of these intermolecular interactions was implemented to understand the charge density redistribution of the molecule in the active site of influenza neuraminidase to validate the strength of the interactions.Communicated by Ramaswamy H. Sarma.

Comparative Study of Two Chondroitin Sulfate/Dermatan Sulfate 4-O-Sulfatases With High Identity

Chondroitin sulfate/dermatan sulfate (CS/DS) sulfatases are potential tools for structural and functional studies of CD/DS chains. In our previous study, a CS/DS 4-O-endosulfatase (endoVB4SF) was identified from a marine bacterium (Wang et al., 2015). Herein, another CS/DS 4-O-sulfatase (exoPB4SF) was identified from a Photobacterium sp. ExoPB4SF shares an 83% identity with endoVB4SF but showed strict exolytic activity. Comparative studies were performed for both enzymes on the basis of biochemical features, substrate-degrading patterns and three-dimensional structures. exoPB4SF exhibited a wider temperature and pH adaptability and better thermostability than endoVB4SF. Furthermore, exoPB4SF is a strict exolytic sulfatase that only releases the sulfate group from the GalNAc residue located at the reducing end, whereas endoVB4SF preferentially removed sulfate esters from the reducing end toward the non-reducing end though its directional degradation property was not strict. In addition, the structure of endoVB4SF was determined by X-ray crystallography at 1.95 Å. It adopts a globular conformation with two monomers per asymmetric unit. The exoPB4SF structure was constructed by homology modeling. Molecular docking results showed that although the residues around the catalytic center are conserved, the residues at the active site of endoVB4SF adopted a more favorable conformation for the binding of long CS/DS chains than those of exoPB4SF, which may explain why the two highly homogenous sulfatases possessed different action patterns. The results of this study provide insight into the structure-function relationship of CS/DS endo- and exosulfatases for the first time.

Identification of potential Mycobacterium tuberculosis topoisomerase I inhibitors: a study against active, dormant and resistant tuberculosis

Mycobacterium tuberculosis (Mtb) topoisomerase I (Topo I), involved in the relaxation of negatively supercoiled DNA, plays an important role in the viability of pathogen Mtb. Being one of the most significant enzymes; it also takes part in crucial biological pathways such as transcription and replication of the pathogen. The present study aims at the development of Mtb Topo I 3D protein structure which in turn was employed for the virtual screening of compound libraries in a process of identification of a hit molecule. The identified hit, hydroxycamptothecin, was active at 6.25 μM which was further derivatized synthetically into fifteen novel analogues. Among these, four compounds (3b, 3g, 3h and 3l) emerged to be active displaying IC50 values ranging from 2.9 to 9.3 μM against Mtb Topo I and were non-cytotoxic at 25 μM. These four compounds also proved their efficacy when tested against active, dormant and resistant forms of Mtb. The most potent inhibitor 3b was screened for in vivo anti-mycobacterial activity using zebrafish model and was found to be more effective when compared to first line anti-tubercular drugs, isoniazid and rifampicin. The binding affinity of this compound towards Mtb Topo I was analyzed by differential scanning fluorimetry which resulted in a positive shift in melting temperature when compared to the native protein thereby proving its stabilization effect over protein.

Exploration of fluoroquinolone resistance in Streptococcus pyogenes: comparative structure analysis of wild-type and mutant DNA gyrase

Quinolone resistance-determining region is known to be the druggability site of the target protein that undergoes frequent mutation and thus renders quinolone resistance. In the present study, ligands were tested for their inhibitory activity against DNA gyrase of Streptococcus pyogenes involved in DNA replication. In silico mutational analysis on modelled gyrase A revealed that GLU85 had the most possible interactions with all the ligands used for the study. The amino acid residue GLU85 had also been predicted with an essential role of maintaining the three-dimensional structure of the protein. When introduced with a mutation (GLU 85 LYS) on this particular residue, it had readily denatured the whole α-helix (from 80 to 90 amino acids). This was confirmed through the molecular dynamics simulation and revealed that this single mutation can cause many functional and structural changes. Furthermore, LYS85 mutation has altered the original secondary structure of the protein, which in turn led to the steric hindrance during the ligand-receptor interaction. The results based on the G-score revealed that ligands have reduced interaction with the mutant protein. The semisynthetic fluoroquinolone 6d, which is an exception, forms a strong interaction with the mutant protein and was experimentally verified using the antimicrobial test. Hence, the present study unravels the fact that mutation at the drug binding site is the major cause for different level of resistance by the S. pyogenes when exposed against the varying concentrations of the fluoroquinolones. Furthermore, a comparative assessment of quinolone derivative with the older generation fluoroquinolones will be of great impact for S. pyogenes-related infections.

Induction of supramolecular chirality in di-zinc(II) bisporphyrin via tweezer formation: synthesis, structure and rationalization of chirality

Two new supramolecular complexes consisting of an achiral bisporphyrin host and a chiral diamine guest are reported. One shows a remarkably high amplitude bisignate CD signal while the other one shows a very low value. X-ray structure and other spectroscopic investigations of the tweezer complexes clearly rationalize the origin of the optical activity that has so far remained an unresolved issue.