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Structural significance of conformational preferences and ribose ring puckering of newly discovered hyper modified nucleotide, 5'-monophosphate 2-methylthio cyclic N 6 -threonylcarbamoyladenosine (p-ms 2 ct 6 A) have been investigated using quantum chemical semi-empirical RM1 and molecular dynamics simulation techniques. Automated geometry optimization of most stable structure of p-ms 2 ct 6 A has also been carried out with the help of abinitio (HF SCF, DFT) as well as semi empirical quantum chemical (RM1, AM1, PM3, and PM6) methods. Most stable structure of p-ms 2 ct 6 A is stabilized by intramolecular interactions between N(3)…HC(2'), N(1)…HC(16), O(13)…HC(15), and O(13)…HO(14). The torsion angles alpha (α) and beta (β) show the significant characteristic patterns with the involvement of intramolecular hydrogen bonding to provide stability to the p-ms 2 ct 6 A. Further, molecular dynamics simulations of p-ms 2 ct 6 A revealed the role of ribose sugar ring puckering i.e. C2'-endo and C3'-endo on the structural dynamics of ms 2 ct 6 A side chain. The modified nucleotide p-ms 2 ct 6 A periodically prefers both the C2'-endo and C3'-endo sugar with 'anti' and 'syn' conformations. This property of p-ms 2 ct 6 A could be useful to recognize the starting ANN codons. All atom explicit MD simulation of anticodon loop (ACL) of tRNA Lys of Bacillus subtilis containing ms 2 ct 6 A at 37th position showed the U-turn feature, base stacking ability with other adjacent bases and hydrogen bonding interactions similar to the isolated base p-ms 2 ct 6 A. The ribose sugar puckering contributes to the orientation of the side chain conformation of p-ms 2 ct 6 A. Thus, the present study could be helpful to understand the structure-function relationship of the hypermodified nucleoside, ms 2 ct 6 A in recognition of the proper codons AAA/AAG during protein biosynthesis., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Being a part of dormancy survival regulator (DosR) regulon, Rv2004c (rough morphology and virulent strain gene) has been identified in earlier experimental studies as an indispensable protein required for the growth and survival of Mycobacterium tuberculosis . This protein was predicted to have a role in inhibition of phospholipase A2 activity related to immuno-defence and other membrane-related events. Thus, considering significance of Rv2004c protein, a structure-based drug designing strategy was followed to identify potential inhibitors to this novel target. Initially, to validate the target, absence of homologous proteins in the host was verified through sequence and structure similarity search against human proteome. Then, a potential ligand binding site on the target was identified and virtual screening against Zinc database molecules was carried out. The top scoring hits along with their analogs were taken for docking studies with Glide. The binding free energy of the docked complexes of the Glide hits were predicted by Prime program from Schrodinger and molecules ZINC57990006, ZINC33605742, ZINC71773467 and ZINC34198774 were recognized as potential hits against this target. Analyzing the predicted pharmacokinetic properties of the molecules from QikProp and admetSAR tool, ZINC34198774 was identified as a valid molecule. Molecular dynamics simulation studies ascertained that ZINC34198774 could be a potential inhibitor against Rv2004c. Thus, results acquired from this study could be of use to design new therapeutics against tuberculosis.Communicated by Ramaswamy H. Sarma.

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has been responsible for the cause of global pandemic Covid-19 and to date, there is no effective treatment available. The spike 'S' protein of SARS-CoV-2 and ACE2 of the host cell are being targeted to design new drugs to control Covid-19. Similarly, a transmembrane serine protease, TMPRSS2 of the host cell plays a significant role in the proteolytic cleavage of viral 'S' protein helpful for the priming of ACE2 receptors and viral entry into human cells. However, three-dimensional structural information and the inhibition mechanism of TMPRSS2 is yet to be explored experimentally. Hence, we have used a molecular dynamics (MD) simulated homology model of TMPRSS2 to study the inhibition mechanism of experimentally known inhibitors Camostat mesylate, Nafamostat and Bromhexine hydrochloride (BHH) using molecular modeling techniques. Prior to docking, all three inhibitors were geometry optimized by semi-empirical quantum chemical RM1 method. Molecular docking analysis revealed that Camostat mesylate and its structural analogue Nafamostat interact strongly with residues His296 and Ser441 present in the catalytic triad of TMPRSS2, whereas BHH binds with Ala386 along with other residues. Comparative molecular dynamics simulations revealed the stable behavior of all the docked complexes. MM-PBSA calculations also revealed the stronger binding of Camostat mesylate to TMPRSS2 active site residues as compared to Nafamostat and BHH. Thus, this structural information could be useful to understand the mechanistic approach of TMPRSS2 inhibition, which may be helpful to design new lead compounds to prevent the entry of SARS-Coronavirus 2 in human cells., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2021 Published by Elsevier Ltd.)

Transfer RNA remains to be a mysterious molecule of the cell repertoire. With its modified bases and selectivity of codon recognition, it remains to be flexible inside the ribosomal machinery for smooth and hassle-free protein biosynthesis. Structural changes occurring in tRNA due to the presence or absence of wybutosine, with and without Mg 2+ ions, have remained a point of interest for structural biologists. Very few studies have come to a conclusion correlating the changes either with the structure and flexibility or with the codon recognition. Considering the above facts, we have implemented molecular modeling methods to address these problems using multiple molecular dynamics (MD) simulations of tRNA Phe along with codons. Our results highlight some of the earlier findings and also shed light on some novel structural and functional aspects. Changes in the stability of tRNA Phe in native or codon-bound states result from the conformations of constituent nucleotides with respect to each other. A smaller change in their conformations leads to structural distortions in the base-pairing geometry and eventually in the ribose-phosphate backbone. MD simulation studies highlight the preference of UUC codons over UUU by tRNA Phe in the presence of wybutosine and Mg 2+ ions. This study also suggests that magnesium ions are required by tRNA Phe for proper recognition of UUC/UUU codons during ribosomal interactions with tRNA., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Deficiency of 5-taurinomethyl-2-thiouridine, τm 5 s 2 U at the 34th 'wobble' position in tRNA Lys causes MERRF (Myoclonic Epilepsy with Ragged Red Fibers), a neuromuscular disease. This modified nucleoside of mt tRNA Lys , recognizes AAA/AAG codons during protein biosynthesis process. Its preference to identify cognate codons has not been studied at the atomic level. Hence, multiple MD simulations of various molecular models of anticodon stem loop (ASL) of mt tRNA Lys in presence and absence of τm 5 s 2 U 34 and N 6 -threonylcarbamoyl adenosine (t 6 A 37 ) along with AAA and AAG codons have been accomplished. Additional four MD simulations of multiple ASL mt tRNA Lys models in the context of ribosomal A-site residues have also been performed to investigate the role of A-site in recognition of AAA/AAG codons. MD simulation results show that, ASL models in presence of τm 5 s 2 U 34 and t 6 A 37 with codons AAA/AAG are more stable than the ASL lacking these modified bases. MD trajectories suggest that τm 5 s 2 U recognizes the codons initially by 'wobble' hydrogen bonding interactions, and then tRNA Lys might leave the explicit codon by a novel 'single' hydrogen bonding interaction in order to run the protein biosynthesis process smoothly. We propose this model as the 'Foot-Step Model' for codon recognition, in which the single hydrogen bond plays a crucial role. MD simulation results suggest that, tRNA Lys with τm 5 s 2 U and t 6 A recognizes AAA codon more preferably than AAG. Thus, these results reveal the consequences of τm 5 s 2 U and t 6 A in recognition of AAA/AAG codons in mitochondrial disease, MERRF.

Hypermodified bases present at 3'-adjacent (37 th ) position in anticodon loop of tRNA Phe are well known for their contribution in modulating codon-anticodon interactions. Peroxywybutosine (o2yW), a wyosine family member, is one of such tricyclic modified bases observed at the 37 th position in tRNA Phe . Conformational preferences and three-dimensional structural analysis of peroxywybutosine have not been investigated in detail at atomic level. Hence, in the present study quantum chemical semi-empirical RM1 and multiple molecular dynamics (MD) simulations have been used to study structural significance of peroxywybutosine in tRNA Phe . Full geometry optimizations over the peroxywybutosine base have also been performed using ab-initio HF-SCF (6-31G**), DFT (B3LYP/6-31G**) and semi-empirical PM6 method to compare the salient properties. RM1 predicted most stable structure shows that the amino-carboxy-propyl side chain of o2yW remains 'distal' to the five membered imidazole ring of tricyclic guanosine. MD simulation trajectory of the isolated peroxy base showed restricted periodical fluctuations of peroxywybutosine side chain which might be helpful to maintain proper anticodon loop structure and mRNA reading frame during protein biosynthesis process. Another comparative MD simulation study of the anticodon stem loop with codon UUC showed various properties, which justify the functional implications of peroxywybutosine at 37 th position along with other modified bases present in ASL of tRNA Phe . Thus, this study presents an atomic view into the structural properties of peroxywybutosine, which can be useful to determine its role in the anticodon stem loop in context of codon-anticodon interactions and frame shift mutations., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Lack of naturally occurring modified nucleoside 5-taurinomethyluridine (τm5U) at the 'wobble' 34th position in tRNALeu causes mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). The τm5U34 specifically recognizes UUG and UUA codons. Structural consequences of τm5U34 to read cognate codons have not been studied so far in detail at the atomic level. Hence, 50ns multiple molecular dynamics (MD) simulations of various anticodon stem loop (ASL) models of tRNALeu in presence and absence of τm5U34 along with UUG and UUA codons were performed to explore the dynamic behaviour of τm5U34 during codon recognition process. The MD simulation results revealed that τm5U34 recognizes G/A ending codons by 'wobble' as well as a novel 'single' hydrogen bonding interactions. RMSD and RMSF values indicate the comparative stability of the ASL models containing τm5U34 modification over the other models, lacking τm5U34. Another MD simulation study of 55S mammalian mitochondrial rRNA with tRNALeu showed crucial interactions between the A-site residues, A918, A919, G256 and codon-anticodon bases. Thus, these results could improve our understanding about the decoding efficiency of human mt tRNALeu with τm5U34 to recognize UUG and UUA codons.

Transfer RNAs (tRNAs) contain various uniquely modified nucleosides thought to be useful for maintaining the structural stability of tRNAs. However, their significance for upholding the tRNA structure has not been investigated in detail at the atomic level. In this study, molecular dynamic simulations have been performed to assess the effects of methylated nucleic acid bases, N (2)-methylguanosine (m(2)G) and N (2)-N (2)-dimethylguanosine (m 2 (2) G) at position 26, i.e., the hinge region of E. coli tRNA(Phe) on its structure and dynamics. The results revealed that tRNA(Phe) having unmodified guanosine in the hinge region (G26) shows structural rearrangement in the core of the molecule, resulting in lack of base stacking interactions, U-turn feature of the anticodon loop, and TΨC loop. We show that in the presence of the unmodified guanosine, the overall fold of tRNA(Phe) is essentially not the same as that of m(2)G26 and m 2 (2) G26 containing tRNA(Phe). This structural rearrangement arises due to intrinsic factors associated with the weak hydrogen-bonding patterns observed in the base triples of the tRNA(Phe) molecule. The m(2)G26 and m 2 (2) G26 containing tRNA(Phe) retain proper three-dimensional fold through tertiary interactions. Single-point energy and molecular electrostatics potential calculation studies confirmed the structural significance of tRNAs containing m(2)G26 and m 2 (2) G26 compared to tRNA with normal G26, showing that the mono-methylated (m(2)G26) and dimethylated (m 2 (2) G26) modifications are required to provide structural stability not only in the hinge region but also in the other parts of tRNA(Phe). Thus, the present study allows us to better understand the effects of modified nucleosides and ionic environment on tRNA folding.

Mycobacterium tuberculosis is a Gram positive, acid-fast bacteria belonging to genus Mycobacterium, is the leading causative agent of most cases of tuberculosis. The pathogenicity of the bacteria is enhanced by its developed DNA repair mechanism which consists of machineries such as nucleotide excision repair. Nucleotide excision repair consists of excinuclease protein UvrABC endonuclease, multi-enzymatic complex which carries out repair of damaged DNA in sequential manner. UvrC protein is a part of this complex and thus helps to repair the damaged DNA of M. tuberculosis. Hence, structural bioinformatics study of UvrC protein from M. tuberculosis was carried out using homology modeling and molecular docking techniques. Assessment of the reliability of the homology model was carried out by predicting its secondary structure along with its model validation. The predicted structure was docked with the ATP and the interacting amino acid residues of UvrC protein with the ATP were found to be TRP539, PHE89, GLU536, ILE402 and ARG575. The binding of UvrC protein with the DNA showed two different domains. The residues from domain I of the protein VAL526, THR524 and LEU521 interact with the DNA whereas, amino acids interacting from the domain II of the UvrC protein included ARG597, GLU595, GLY594 and GLY592 residues. This predicted model could be useful to design new inhibitors of UvrC enzyme to prevent pathogenesis of Mycobacterium and so the tuberculosis.