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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 Mg2+ 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 tRNAPhe 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 tRNAPhe 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 tRNAPhe in the presence of wybutosine and Mg2+ ions. This study also suggests that magnesium ions are required by tRNAPhe for proper recognition of UUC/UUU codons during ribosomal interactions with tRNA.

The rapid outbreak of SARS-Coronavirus 2 (SARS-CoV-2) caused a serious global public health threat. The spike ‘S’ protein of SARS-CoV-2 and ACE2 of the host cell are being targeted to design and discover new drugs to control Covid-19 disease. Similarly, a transmembrane serine protease, TMPRSS2 of the host cell has been found to play a significant role in proteolytic cleavage of viral spike protein priming to the receptor ACE2 present in human cell. However, three dimensional structure and inhibition mechanism of TMPRSS2 is yet to be explored experimentally. Hence, in the present study we have generated a homology model of TMPRSS2 and studied its binding properties with experimentally studied inhibitors <i>viz.</i> Camostat mesylate, Nafamostat and Bromhexine hydrochloride (BHH) using molecular docking technique. Docking analysis revealed that the Camostat mesylate and its structural analogue Nafamostat interacts strongly with residues His296, Ser441 and Asp435 present in catalytic triad of TMPRSS2. However, BHH interacts with Gln438 and other residues present in the active site pocket of TMPRSS2 through hydrophobic contacts effectively. Thus, these results revealed the inhibition mechanism of TMPRSS2 by known inhibitors Camostat mesylate, Nafamostat and Bromhexine hydrochloride in detail at the molecular level. However, Camostat mesylate shows strong binding as compared to other two inhibitors. This structural information could also be useful to design and discover new inhibitors of TMPRSS2, which may be helpful to prevent the entry to SARS-Coronavirus 2 in human cell.

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