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CovidReference.com
Hemagglutinin Esterade Protein (HE) There is the presence of an additional structural protein, the hemagglutininesterase (HE) protein, in a subset of Betacoronaviruses such as murine CoVs and the humancoronavirus HKU1. The HE-protein is also located within in viral envelope as a dimer forming short projections of 5-10nm. It functions as a cofactor for the S-protein assisting with viral attachment and transit through extracellular mucosa (Knipe 2013). It is however, is not a feature of SARS-CoV-2.
Genomic Structure and Variation The CoV genome is composed of nonsegmented, single stranded, positive sense RNA ranging from 26-32 kilobases pairs (kbp) in length. Unlike other RNA viruses (whose genomes are generally less than 10kbp), CoV genomes are comparatively extremely large. Structurally they comprise of the same basic features which include: 5’ cap structure, 3’-poly-adenylated tail, 5’ and 3’ untranslated region (UTR), a conserved set of structural and non-structural genes, as well as strain-specific accessory genes. The invariant genes order of all CoV families are arranged in a 5’ to 3’ order as: ORF1a/b (or replicase gene), spike (S), envelope (E), membrane (M), and nucleocapsid (N), with accessory genes interspersed among the structural genes at the 3’ end (Perlman 2020, Chen Y 2020). Between each gene downstream from ORF1a/b, there are short motifs ranging from 6-49 base pairs called transcription regulatory sequences (TRS). TRS play a role in the production of subgenomic RNA (sgRNA) which is discussed later in the chapter (O’Leary 2020). Genomic sequencing of lower respiratory tract samples from index patients in Wuhan, China, identified SARS-CoV-2 as a novel coronavirus. It was thus placed by the CSG within the Coronaviridae family [Lu 2020]. Phylogenetic analysis conducted to determine the relationship of SARS-CoV-2 to other CoV clustered it in the Betacoronavirus genus, Sarbecovirus subgenus [Tan W 2020, Zhu N 2020]. Notably there is 94,4% homology with SARS-CoV in the seven conserved replicase domains in ORF1ab forming a distinct clade within the Severe Acute respiratory syndrome related coronavirus species (SARSr-CoV).
Kamps – Hoffmann
