Computational methods for the prediction of protein folds

In silico analysis of Phyllanthus amarus phytochemicals as potent drugs against SARS-CoV-2 main protease

Phyllanthus amarus, also known as Bhui Korma in India, is well known for its medicinal properties and is used to treat several diseases worldwide. This study aims to identify phytochemicals from P. amarus and assess their anti-viral activity through in silico methods against the main protease (3CL^Pro/M^Pro) enzyme of the novel coronavirus. 190 compounds were obtained from literature and docked against 3CLPro and 16 compounds showed higher binding affinity with 3CL^Pro with their values lying between -8.9 ​kcal/mol to -9.6 ​kcal/mol. The top two compounds, Myricitrin (CID: 5352000) and Quercetin-3-O-glucuronide (CID: 12004528) gave high binding affinity values of -9.6 ​kcal/mol and -9.4 ​kcal/mol respectively and also display favourable binding interactions with the 3CL^Pro. Both the compounds were further subjected to molecular dynamics simulation and MM-PBSA based binding free energy calculations. ADMET and drug-likeness properties were studied to assess the pharmacokinetic properties of the compounds. Favourable pharmacokinetic results reinforced the applicability of the compounds assessed. Along with continuous studies being carried out with chemical compounds, research needs to expand into all areas, including the use of natural compounds as drug compounds. The identified hits from this study can be taken further for in vitro and in vivo studies to examine their efficacy against COVID-19.

Side chain placement using estimation of distribution algorithms

OBJECTIVE

This paper presents an algorithm for the solution of the side chain placement problem.

METHODS AND MATERIALS

The algorithm combines the application of the Goldstein elimination criterion with the univariate marginal distribution algorithm (UMDA), which stochastically searches the space of possible solutions. The suitability of the algorithm to address the problem is investigated using a set of 425 proteins.

RESULTS

For a number of difficult instances where inference algorithms do not converge, it has been shown that UMDA is able to find better structures.

CONCLUSIONS

The results obtained show that the algorithm can achieve better structures than those obtained with other state-of-the-art methods like inference-based techniques. Additionally, a theoretical and empirical analysis of the computational cost of the algorithm introduced has been presented.

Molecular modeling approaches for determining gene function: application to a putative poly-A binding protein from Leishmania amazonensis (LaPABP)

The great expansion in the number of genome sequencing projects has revealed the importance of computational methods to speed up the characterization of unknown genes. These studies have been improved by the use of three dimensional information from the predicted proteins generated by molecular modeling techniques. In this work, we disclose the structure-function relationship of a gene product from Leishmania amazonensis by applying molecular modeling and bioinformatics techniques. The analyzed sequence encodes a 159 amino acids polypeptide (estimated 18 kDa) and was denoted LaPABP for its high homology with poly-A binding proteins from trypanosomatids. The domain structure, clustering analysis and a three dimensional model of LaPABP, basically obtained by homology modeling on the structure of the human poly-A binding protein, are described. Based on the analysis of the electrostatic potential mapped on the model's surface and conservation of intramolecular contacts responsible for folding stabilization we hypothesize that this protein may have less avidity to RNA than it's L. major counterpart but still account for a significant functional activity in the parasite. The model obtained will help in the design of mutagenesis experiments aimed to elucidate the mechanism of gene expression in trypanosomatids and serve as a starting point for its exploration as a potential source of targets for a rational chemotherapy.

Proteins can adopt totally different folded conformations

The three-dimensional structure of a protein is determined by interactions between its amino acids and by interactions of the amino acids with molecules of the environment. The great influence of the latter interactions is demonstrated for the enzyme phosphoglycerate kinase from yeast (PGK). In the native state, PGK is a compact, bilobal molecule; 35% and 13% of its amino acids are organised in the form of alpha-helices and beta-sheets, respectively. The molecules unfold at acidic pH and low ionic strength forming random-walk structures with a persistence length of 3 nm. More than 90% of the amino acid residues of the ensemble have phi,psi-angles corresponding to those of a straight beta-chain. Upon addition of 50% (v/v) trifluoroethanol to the acid-unfolded protein, the entire molecule is transformed into a rod-like, flexible alpha-helix. Addition of anions, such as chloride or trichloroacetate, to the acid-unfolded protein leads to the formation of amyloid-like fibres over a period of many hours when the anion concentration exceeds a critical limit. Half of the amino acid residues are then organised in beta-sheets. Both of the non-natively folded states of PGK contain more regular secondary structure than the native one. The misfolding starts in both cases from the acid-unfolded state, in which the molecules are essentially more expanded than in other denatured states, e.g. those effected by temperature or guanidine hydrochloride.

Prediction of protein tertiary structure to low resolution: performance for a large and structurally diverse test set

We report the tertiary structure predictions for 95 proteins ranging in size from 17 to 160 residues starting from known secondary structure. Predictions are obtained from global minimization of an empirical potential function followed by the application of a refined atomic overlap potential. The minimization strategy employed represents a variant of the Monte Carlo plus minimization scheme of Li and Scheraga applied to a reduced model of the protein chain. For all of the cases except beta-proteins larger than 75 residues, a native-like structure, usually 4-6 A root-mean-square deviation from the native, is located. For beta-proteins larger than 75 residues, the energy gap between native-like structures and the lowest energy structures produced in the simulation is large, so that low RMSD structures are not generated starting from an unfolded state. This is attributed to the lack of an explicit hydrogen bond term in the potential function, which we hypothesize is necessary to stabilize large assemblies of beta-strands.

The protein state of matter

Three ways are generally used to visualize proteins: (1) a static model in which the atomic positions are defined, (2) a dynamic model taking into account fluctuations, and (3) a reactive model that reflects the internal and external electric fields of the molecule. The properties of chromophoric prosthetic groups can be probed by optical spectroscopy, and when high resolution techniques are used, the results reveal information about the local electric fields in proteins, as influenced and determined by atomic positions and dynamics.