1  Introduction
The present pandemic situation of the Severe Acute Respiratory Syndrome (COVID-19) is caused by the RNA virus SARS-CoV2 which is characterized by its rapid mutations up to a million times higher than that of their hosts [1]. Several mutations have been detected in various proteins of the SARS-CoV2 over a short period of time, which are recently reported in various articles [[2], [3], [4]]. Genomic variations and evolution enabled the virus to escape host immunity [5,6]. So, such variability would help the scientists towards the drug development [1]. Among various proteins of SARS-CoV2, spike(S), envelope (E), membrane(M) and nucleocapsid (N) are the four structural proteins which help them in assembling and releasing new copies of the virus within human cell [7].
The CoV envelope (E) protein is the smallest among the four structural proteins involved in several aspects of the virus life cycle, such as assembly, budding, envelope formation, and pathogenesis [7]. However, the molecular mechanism involving E-protein in pathogenesis is not yet clearly understood. Notably, this protein interacts with other structural proteins such as membrane(M) and other accessory proteins viz. ORF3a, ORF7a and host cell proteins [8]. Envelope protein of SARS-CoV2 is 76 amino acids long and possesses three important domains viz. (N)-terminus, transmembrane domain (TMD) and (C)-terminus (Fig. 1 ). The (C)-terminal domain of envelope protein in SARS-CoV2 binds to human PALS1, a tight junction-associated protein, which is essential for the establishment and maintenance of epithelial polarity in mammals [9,10].
Fig. 1 Amino acid sequence and domains of the envelope protein of SARS-CoV2 [7].
Red and blue colors are representing hydrophobic and hydrophilic amino acid, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Four mutations including one deletion have been found in the envelope protein of SARS-CoV2 with reference to the SARS-CoV1, a species of coronavirus that also infects humans, bats and certain other mammals. The alignment of the envelope proteins of the SARS-CoV1 and SARS-CoV2 is given in Fig. 2 .
Fig. 2 Clustal alignment of the envelope protein of SARS-CoV1 and SARS-CoV2.
Mutations in (C)-terminus domain in the E protein protein of SARS-CoV2 are T55S, V56F, E69R (the mutation of an amino acid A1 to an amino acid A2 is denoted by A1pA2 where p denotes location in the reference amino acid sequence).The deletion mutation of G at the 70th position with respect to the reference envelope protein of SARS-CoV1 is also noted.
It is reported that the C-terminus domain of the envelope protein contains the motif DLLV which binds to the host cell PALS1 protein to facilitate infection [9,11,12].
In this present study, non-synonymous mutations over the envelope protein of SARS-CoV2 across the available 3617 SARS-CoV2 genomes (as on 6th June 2020), have been found and accordingly their probable consequences are discussed.