![]() The CoV outbreaks are highly likely to be unavoidable in the future due to climate and ecology changes, and increased human-animal interactions. It has been suggested that spike protein, envelope protein, membrane protein, nucleocapsid protein, 3CL protease, papain such as protease, RNA polymerase, and helicase protein are viable antiviral drug targets. Comparatively, the SARS-CoV-2 lacks the hemagglutinin esterase gene found in other human coronavirus (hCoV) HKU1, a lineage A betacoronavirus, ]. While accessory proteins have been found to be dispensable for in vitro viral replication, others have been shown to play a significant role in in vivo virus-host interactions. The SARS-CoV proteins consist of two large polyproteins: ORF1a and ORF1ab (which cleavage proteolytically to shape 16 non-structural proteins) ( Table 1 The outbreaks of severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and coronavirus disease 2019 (COVID-19) have shown the potential for transmission of newly emerging CoVs from animal to human and human to human. While CoVs can infect many hosts, the coronaviruses infecting humans are all belonging to either alpha- or beta- CoVs. Alternatively, coronaviruses are divided into four genera on the basis of genetic and serologic properties Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus in the subfamily Coronavirinae, ,, ]. The current classification of coronaviruses recognizes 39 species in 27 subgenera, five genera and two subfamilies that belong to the family Coronaviridae, suborder Cornidovirineae, order Nidovirales and realm Riboviria. They can infect human, livestock, birds, bat, mouse and many other wild animals with the respiratory, gastrointestinal, hepatic and central nervous system infections, , ]. Therefore, it is crucial to understand the structure, function, and interactions of coronaviruses RNA synthesizing machinery and their replication strategies.Ĭoronaviruses (CoVs) are major threats to humans and vertebrate species. Besides that, several smaller subunits (nsp 7– nsp 10) serve as essential cofactors for these enzymes and contribute to the emerging “nsp interactome.” In spite of the significant progress in studying coronaviruses structural and functional properties, there is an urgent need to understand the coronaviruses evolutionary success that will be helpful to develop enhanced control strategies. Coronavirus replicase has more or less universal activities, such as RNA polymerase (nsp 12) and helicase (nsp 13), as well as a variety of unusual or even special mRNA capping (nsp 14, nsp 16) and fidelity regulation (nsp 14) domains. Non-structural proteins (nsp) 7–16 are cleaved from two large replicase polyproteins and guide the replication and processing of coronavirus RNA. Coronavirus have the largest RNA genomes (~26–32 kilobases) and their expansion was likely enabled by acquiring enzyme functions that counter the commonly high error frequency of viral RNA polymerases. All CoVs belong to the order Nidovirales, family Coronaviridae, are enveloped positive-sense RNA viruses, characterised by club-like spikes on their surfaces and large RNA genome with a distinctive replication strategy. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly emerging respiratory virus and is causing CoVID-19 with high morbidity and considerable mortality. These viruses can infect respiratory, gastrointestinal, hepatic and central nervous systems of human, livestock, birds, bat, mouse, and many wild animals. Coronaviruses (CoVs) are causing a number of human and animal diseases because of their zoonotic nature such as Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19).
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