In tropical and subtropical zones, arboviruses are among the major threats to human life, affecting a large number of populations with serious diseases. Worldwide, over three hundred million people are infected with dengue virus (DENV) every year as per the World Health Organization (WHO). DENV-mediated disease severity ranges from a mild fever to hemorrhagic fever and shock syndrome. Patients suffering from severe infection might experience multi-organ failure, cardiomyopathy and even encephalopathy, further complicating the disease pathogenesis. In life-threatening cases, DENV has been reported to affect almost all organs of the human body. In this review, we discuss the organ tropism of DENV in humans in depth as detected in various autopsy studies. Keeping in mind the fact that there is currently no DENV-specific antiviral, it is of utmost importance to achieve a vivid picture of the susceptible cells in humans which might help in designing antivirals against DENV, especially targeting those tissues in which infection might lead to life-threatening conditions.

1. The open reading frame (ORF) 1ab of SARS-CoV2 encodes non-structural proteins involved in viral RNA functions like translation and replication including nsp1-4; 3C like proteinase; nsp6-10; RNA dependent RNA polymerase (RdRp); helicase and 3’-5’ exonuclease. Sequence analyses of ORF1ab unravelled emergence of mutations especially in the viral RdRp and helicase at specific positions, both of which are important in mediating viral RNA replication. Since proteins are dynamic in nature and their functions are governed by the molecular motions, we performed normal mode analyses of the SARS-CoV2 wild type and mutant RdRp and helicases to understand the effect of mutations on their structure, conformation, dynamics and thus function. Structural analyses revealed that mutation of RdRp (at position 4715 in the context of the polyprotein/ at position 323 of RdRp) leads to rigidification of structure and that mutation in the helicase (at position 5828 of polyprotein/ position 504) leads to destabilization increasing the flexibility of the protein structure. Such structural modifications and protein dynamics alterations might alter unwinding of complex RNA stem loop structures, the affinity/ avidity of polymerase RNA interactions and in turn the viral RNA replication. The mutation analyses of proteins of the SARS-CoV2 RNA replication complex would help targeting RdRp better for therapeutic intervention.

Till date there are three full length COVID 19 virus genome sequences available from India. The earlier two were reported from Kerala, Southern India and the more recent one has been reported from Gujarat, western part of India. In this paper we report two novel mutations in the Spike protein sequence of Gujarat’s isolate. These mutations are based on comparison with the original Wuhan sequence. The two mutations have been found to be located just upstream and downstream of the receptor binding domain (RBD). Out of these two one has also been found to affect the secondary structure of the S1 domain. Since both of these mutations lie near the receptor binding domain, they might influence the spike receptor interactions by changing the conformation of the spike protein S1 domain. These mutations are uniquely placed and might be important in the context of vaccine engineering and therapeutic interventions.

India has recently started sequencing SARS-CoV2 genome from clinical isolates. Currently only few sequences are available from three states in India. Kerala was the first state to deposit complete sequence from two isolates followed by one from Gujarat. On April 27, 2020, the first five sequences from the state of West Bengal (Eastern India) were deposited on ‘a global initiative on sharing avian flu data’ (GISAID) platform. In this paper we have analysed the spike protein sequences from all these five isolates and also compared for their similarities or differences with other sequences reported in India and with isolates of Wuhan origin. We report one unique mutation at position 723 and the other at 1124 in the S2 domain of spike protein of the isolates from West Bengal only and one mutation downstream of the receptor binding domain at position 614 in S1 domain which was common with the sequence from Gujarat (a state of western part of India). Mutation in the S2 domain showed changes in the secondary structure of the spike protein at region of mutation. We also studied molecular dynamics using normal mode analyses and found that this mutation decreases the flexibility of S2 domain. Since both S1 and S2 are important in receptor binding followed by entry in the host cells, such mutations may define the affinity or avidity of receptor binding.

RNA helicases play pivotal role in RNA replication by catalysing the unwinding of complex RNA duplex structures into single strands in ATP/NTP dependent manner. SARS coronavirus 2 (SARS-CoV-2) is a single stranded positive sense RNA virus belonging to the family Coronaviridae . The viral RNA encodes non structural protein Nsp13 or the viral helicase protein that helps the viral RNA dependent RNA polymerase (RdRp) to execute RNA replication by unwinding the RNA duplexes. In this study we identified a novel mutation at position 541of the helicase where the tyrosine (Y) got substituted with cytosine (C). We found that Y541C is a destabilizing mutation increasing the molecular flexibility and leading to decreased affinity of helicase binding with RNA. Earlier we had reported a mutation P504L in the helicase protein for which had not performed RNA binding study. Here we report that P504L mutation leads to increased affinity of helicase RNA interaction. So, both these mutations have opposite effects on RNA binding. Moreover, we found a significant fraction of isolate population where both P504L and Y541C mutations were co-existing.

Spike (S) protein of Coronaviruses help in receptor attachment and virus entry into the host cells. While S protein is required for virus entry, it is also important as an immunogen as it is the most accessible part of the virus architecture. S protein form knob like structures (viral spikes) protruding outwards in the form of homotrimers containing an S1 and S2 as monomers. Mutations in structural proteins of virus play crucial role in determining virulence and also in many instances influencing emergence of antibody escape variants and cellular tropism. In this paper we have performed in depth analyses of spike protein sequences from various parts of the world and tried to correlate the data with possible functional relevance of such mutations.