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Amino acid side chains are key to fine-tuning the microenvironment polarity in proteins composed of polar amide bonds. Here, we report that substituting an oxygen atom of the backbone amide bond with sulfur atom desolvates the thioamide bond, thereby increasing its lipophilicity. The impact of such local desolvation by O to S substitution in proteins was tested by synthesizing thioamidated variants of Pin1 WW domain. We observe that a thioamide acts in synergy with nonpolar amino acid side chains to reduce the microenvironment polarity and increase protein stability by more than 14 °C. Through favorable van der Waals and hydrogen bonding interactions, this single atom substitution significantly stabilizes proteins without altering the amino acid sequence and structure of the native protein.

Most of the therapeutic drugs available in the market today, are targeted against proteins. Drug molecules are designed to complement shape, size and electrostatic fingerprints of the functional site of a target protein so that they can bind to the protein and impede its molecular function. Details of functional site are derived from 3-D structure of the protein obtained either through experimental techniques or computational protein modeling and form the basis for structure-based drug design. Knowledge derived from homologous proteins facilitates this process by providing an understanding on common and unique features of the intended target with respect to its close and distant relatives. This helps to design a drug with high selectivity and affinity. Often inherent dynamic nature of proteins facilitates inter-protein interactions and aid them to perform major cellular activities as an assembled complex. With improved apprehension of structural biology, consideration of multi-protein machineries and their associated conformational dynamics is increasingly gaining importance in drug design and discovery. Susceptibility of protein-protein interactions in disease conditions is progressively being realized and this has attracted protein-protein interfaces as potential drug targets for therapeutic intervention in the last few decades. In this chapter, we have discussed the properties of protein structure, evolution, dynamics and protein complexes along with explanations on how each factor contributes to the design of an effective drug molecule that is safe and efficacious.

The conventional drug discovery pipeline involving discovery of a new molecule requires huge investment and long time. Therefore, re-using the existing drugs for new indication which is termed as “drug repurposing” is of growing importance to the scientific community. The current pandemic has further reinforced the importance of drug repurposing especially when the world is looking forward to a quick and effective solution to treat Covid19. Computational approaches play a crucial role in hastening the overall drug repurposing pipeline. In this chapter, we discuss how the knowledge on protein sequence, structure, and dynamics can be exploited to search for potential anti-Covid19 molecules from the repertoire of approved/under-trial drugs by using various computational tools and resources. Over the past few years, our group has been involved in repurposing drugs against various diseases including Covid19. The learning from our experiences which could improve the reliability on the computational predictions has also been discussed. Overall, this chapter provides a bird's-eye view of various computational methods which can be efficiently used to repurpose drugs against any disease. We hope especially the non-experts in the field could be benefitted from our learning we are sharing in this chapter.

Direct massively parallel sequencing of SARS-CoV-2 genome was undertaken from nasopharyngeal and oropharyngeal swab samples of infected individuals in Eastern India. Seven of the isolates belonged to the A2a clade, while one belonged to the B4 clade. Specific mutations, characteristic of the A2a clade, were also detected, which included the P323L in RNA-dependent RNA polymerase and D614G in the Spike glycoprotein. Further, our data revealed emergence of novel subclones harbouring nonsynonymous mutations, viz. G1124V in Spike (S) protein, R203K, and G204R in the nucleocapsid (N) protein. The N protein mutations reside in the SR-rich region involved in viral capsid formation and the S protein mutation is in the S2 domain, which is involved in triggering viral fusion with the host cell membrane. Interesting correlation was observed between these mutations and travel or contact history of COVID-19 positive cases. Consequent alterations of miRNA binding and structure were also predicted for these mutations. More importantly, the possible implications of mutation D614G (in SD domain) and G1124V (in S2 subunit) on the structural stability of S protein have also been discussed. Results report for the first time a bird’s eye view on the accumulation of mutations in SARS-CoV-2 genome in Eastern India. Electronic supplementary material The online version of this article (10.1007/s12038-020-00046-1) contains supplementary material, which is available to authorized users.

The ongoing global pandemic of COVID-19 has brought life to almost stand still with implementations of lockdown and social distancing as some of the preventive measures in the absence of any approved specific therapeutic interventions. To combat this crisis, research community world-wide are falling back on the existing repertoire of approved/investigational drugs to probe into their anti-coronavirus properties. In this report, we have described our unique efforts in identifying potential drugs that could be repurposed against main protease of SARS-CoV-2 (SARS-CoV-2 Mpro). To achieve this goal, we have primarily exploited the principles of ‘neighbourhood behaviour’ in protein 3-D (workflow-I) and chemical 2-D structural space (workflow-II) coupled with docking simulations and insights into the possible mode of actions of the selected candidates from available literature. Such an integrative approach culminated in prioritizing 29 potential repurpose-able agents (20 approved drugs and 9 investigational molecules) against SARS-CoV-2 Mpro. Apart from the approved/investigational anti-viral drugs, other notable hits include anti-bacterial, anti-inflammatory, anti-cancer and anti-coagulant drugs. Our analysis suggests that some of these drugs have the potential to simultaneously modulate the functions of viral proteins and host response system. Interestingly, many of these identified candidates (12 molecules from workflow-I and several molecules belonging to the chemical classes of alkaloids, tetracyclines, peptidomimetics from workflow-II) are suggested to possess anti-viral properties which are supported by laboratory and clinical data. Further, this work opens a new avenue of research to probe into the molecular mechanism of action of many drugs which are known to demonstrate anti-viral activity but are so far not known to target viral proteases. Our findings should only be used for research purposes and we strongly urge that no individual should interpret these findings for any self-diagnosis or self-medication without the prior approval from competent international health/medical regulatory agencies.

The current global crisis due to COVID-19 has almost brought normal life to standstill in most parts of the world. With our research interest on repurposing known drugs/drug candidates targeting various diseases, we decided to analyse the available data on the deadly pathogen that has already taken thousands of lives since its outbreak in China in December 2019. Our host institute is now shutdown and we are confining ourselves to our homes with limited access to computational resources. Using a simple in silico approach based on the principle of ‘neighbourhood behaviour’ in three-dimensional (3D) space and two-dimensional (2D) space of protein and small molecules respectively, we have identified potential drugs/drug candidates which can be repurposed against protein targets encoded by the SARS-CoV-2 genome. Based on our preliminary analysis, we have so far prioritized more than 20 known drugs/drug candidates which might elucidate anti-coronavirus properties by binding to main protease of the pathogen. These drugs belong to diverse therapeutic areas such as antiviral, anticancer, antibacterial agents etc. Notably, apart from many synthetic molecules, our analysis also hints that phytochemicals obtained from vinca plant (vinca alkaloids) and camptotheca tree (camptothecin and its derivatives) have the potential to bind to main protease of SARS-CoV-2. In-depth investigation on our findings are currently on-going. Here we are presenting the results we obtained so far. The sole purpose of making these preliminary findings openly available to the community is for the experimental biologists and biomedical researchers to investigate our predictions in experimental set ups and for the clinicians to evaluate the potential of these findings for anti-COVID-19 treatment. Our findings should only be used for research purposes and we strongly urge that no individual should interpret these findings for any self-diagnosis or self-medication without the prior approval from competent international health/medical regulatory agencies.

Thioamide substitution into macrocyclic peptides increases the conformational rigidity of the backbone resulting in enhanced biological activity and metabolic stability., We show that substituting a single atom, O to S (amide to thioamide), in a peptide bond results in global restriction of the conformational flexibility in peptide macrocycles with minimal perturbation of the parent conformation. The van der Waals interactions between the C 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 S group and the surrounding atoms are the major driving force in inducing the conformational restriction, resulting in well-defined structures of these cyclic peptides with static 3-D presentation of the pharmacophores. Utilizing this property of thioamides, we report the development of a superactive antagonist of pro-angiogenic αvβ3, αvβ5 and α5β1 integrins, which are responsible for cancer cell proliferation and survival. Using simple thio-scanning and spatial screening of a non-efficacious and conformationally flexible cyclic peptide, we could achieve a more than 105 fold enhancement in its efficacy in cellulo via a single O to S substitution. The developed peptide shows better efficacy in inhibiting the pro-angiogenic integrins than the drug candidate cilengitide, with a significantly enhanced serum half-life of 36 h compared to that of cilengitide (12 h). The long shelf-life, absence of non-specific toxicity and resistance to degradation of the thioamidated macrocyclic peptides in human serum suggest the promise of thioamides in markedly improving the affinity, efficacy and pharmacology of peptide macrocycles.

The ongoing global pandemic of COVID-19 has brought life to almost a standstill with the implementation of lockdowns and social distancing as some of the preventive measures in the absence of any approved specific therapeutic interventions. To combat this crisis, research communities worldwide are falling back on the existing repertoire of approved/investigational drugs to probe into their anti-coronavirus properties. In this report, we describe our unique efforts in identifying potential drugs that could be repurposed against the main protease of SARS-CoV-2 (SARS-CoV-2 Mpro). To achieve this goal, we have primarily exploited the principles of 'neighbourhood behaviour' in the protein 3D (workflow-I) and chemical 2D structural space (workflow-II) coupled with docking simulations and insights into the possible modes of action of the selected candidates from the available literature. This integrative approach culminated in prioritizing 29 potential repurpose-able agents (20 approved drugs and 9 investigational molecules) against SARS-CoV-2 Mpro. Apart from the approved/investigational anti-viral drugs, other notable hits include anti-bacterial, anti-inflammatory, anti-cancer and anti-coagulant drugs. Our analysis suggests that some of these drugs have the potential to simultaneously modulate the functions of viral proteins and the host response system. Interestingly, many of these identified candidates (12 molecules from workflow-I and several molecules, belonging to the chemical classes of alkaloids, tetracyclines, peptidomimetics, from workflow-II) are suggested to possess anti-viral properties, which is supported by laboratory and clinical data. Furthermore, this work opens a new avenue of research to probe into the molecular mechanism of action of many drugs, which are known to demonstrate anti-viral activity but are so far not known to target viral proteases.

The human genome encodes more than 500 protein kinases that regulate numerous crucial cell-signaling pathways, and their dysregulation triggers many diseases including cancer. The Aurora kinases constitutes one of the subfamilies of kinases that are attractive drug targets in anticancer therapy as they play pivotal roles in cell division. Although there are a handful of known Aurora kinase inhibitors, yet there are no approved drugs targeted against these kinases. In this study, we have identified potential Aurora kinase inhibitors from among the repertoire of Food and Drug Administration–approved drugs. We largely adopted a ligand-centric approach that uses the information on shape and chemical features of known inhibitors of Aurora kinases as filter to screen for new molecules possessing similar shape and chemical features. Our analysis identified several approved molecules currently used in diverse therapeutic areas (antivirals, antiinflammatory, anticonvulsant, antiulcer drugs, etc.), which could be probed further to repurpose against Aurora kinases for the treatment of cancer.

Tuberculosis (TB) is a global health concern, and this situation has further worsened due to the emergence of drug-resistant strains and the failure of BCG vaccine to impart protection. There is an imperative need to develop highly sensitive, specific diagnostic tools, novel therapeutics, and vaccines for the eradication of TB. In the present study, a chemical screen of a pharmacologically active compound library was performed to identify antimycobacterial compounds. The phenotypic screen identified a few novel small-molecule inhibitors, including NU-6027, a known CDK-2 inhibitor. We demonstrate that NU-6027 inhibits Mycobacterium bovis BCG growth in vitro and also displayed cross-reactivity with Mycobacterium tuberculosis protein kinase D (PknD) and protein kinase G (PknG). Comparative structural and sequence analysis along with docking simulation suggest that the unique binding site stereochemistry of PknG and PknD accommodates NU-6027 more favorably than other M. tuberculosis Ser/Thr protein kinases. Further, we also show that NU-6027 treatment induces the expression of proapoptotic genes in macrophages. Finally, we demonstrate that NU-6027 inhibits M. tuberculosis growth in both macrophage and mouse tissues. Taken together, these results indicate that NU-6027 can be optimized further for the development of antimycobacterial agents.

Our understanding of the structure–function relationships of biomolecules and thereby applying it to drug discovery programs are substantially dependent on the availability of the structural information of ligand–protein complexes. However, the correct interpretation of the electron density of a small molecule bound to a crystal structure of a macromolecule is not trivial. Our analysis involving quality assessment of ~0.28 million small molecule–protein binding site pairs derived from crystal structures corresponding to ~66,000 PDB entries indicates that the majority (65%) of the pairs might need little (54%) or no (11%) attention. Out of the remaining 35% of pairs that need attention, 11% of the pairs (including structures with high/moderate resolution) pose serious concerns. Unfortunately, most users of crystal structures lack the training to evaluate the quality of a crystal structure against its experimental data and, in general, rely on the resolution as a ‘gold standard’ quality metric. Our work aims to sensitize the non-crystallographers that resolution, which is a global quality metric, need not be an accurate indicator of local structural quality. In this article, we demonstrate the use of several freely available tools that quantify local structural quality and are easy to use from a non-crystallographer’s perspective. We further propose a few solutions for consideration by the scientific community to promote quality research in structural biology and applied areas.

The current public-health burden caused by invasive fungal infections, especially by Candida albicans, is becoming a growing concern due to the emergence of antifungal drug resistance, further compounded by availability of a limited antifungal armament. Indeed, this calls for the development of new formulations for antifungal agents. Concomitantly, several research groups have sought to improve treatment via different strategies, such as combinatorial therapy or boosting the host's immune response through vaccines. In this article, we describe an in silico drug-repurposing strategy to identify potential anticandida agents from the existing repertoire of Food and Drug Administration-approved drugs by means of the comparative analyses of targets of approved drugs and proteins of C. albicans. We identified 26 approved drugs with antifungal potential that can be repurposed against 31 protein targets of C. albicans. Through chemical similarity searches we identified an additional set of 33 approved drugs that may have an inhibitory effect on C. albicans. The drug-target associations made in our study have the potential to further clinical investigations related to the antifungal drug-development pipeline.

Drug repurposing has garnered much interest as an effective method for drug development among biopharmaceutical companies. The availability of information on complete sequences of genomes and their associated biological data, genotype-phenotype-disease relationships, and properties of small molecules offers opportunities to explore the repurpose-able potential of existing pharmacopoeia. This method gains further importance, especially, in the context of development of drugs against infectious diseases, some of which pose serious complications due to emergence of drug-resistant pathogens. In this article, we describe computational means to achieve potential repurpose-able drug candidates that may be used against infectious diseases by exploring evolutionary relationships between established targets of FDA-approved drugs and proteins of pathogen of interest.