INTRODUCTION

Over the past 2 decades, coronaviruses (CoVs) have been associated with significant

disease outbreaks in East Asia and the Middle East. The severe acute respiratory

syndrome (SARS) and the Middle East respiratory syndrome (MERS) began to

emerge in 2002 and 2012, respectively. Recently, a novel coronavirus, severe acute

respiratory syndrome coronavirus 2 (SARS-CoV-2), causing coronavirus disease

2019 (COVID-19), emerged in late 2019, and it has posed a global health threat,

causing an ongoing pandemic in many countries and territories (1).

Health workers worldwide are currently making efforts to control further

disease outbreaks caused by the novel COV (originally named 2019-nCoV), which

was first identified in Wuhan City, Hubei Province, China, on 12 December 2019. On

I l February 2020, the World Health Organization (WHO) announced the official

designation for the current CoV-associated disease to be COVID-19, caused by

SARS-CoV-2. The primary cluster of patients was found to be connected with the

Huanan South China Seafood Market in Wuhan (2). COVs belong to the family

Coronaviridae (subfamily Coronavirinae), the members of which infect a broad

trunerlc Sl locates itsell on top 01 the S 2 stalk (45). Recently, structural analyses of

the S proteins of COVID-19 have revealed 27 amino acid substitutions within a

1,273-ammo-acld stretch (16)Six substitutions are located in the RBI) (amino acids

357 to 528), while four substitutions are in the RBM at the CTD of the Sl domain

(16). Of note, no amino acid change is seen in the RBM, which binds directly to the

angiotensin-converting enzyme-2 (ACE2) receptor in SARS-CoV (16, 46). At

present, the main emphasis is knowing how many differences would be required to

change the host tropism. Sequence comparison revealed 17 nonsynonymous changes

between the early sequence of SARS-CoV-2 and the later isolates of SARS-CoV, The

changes were found scattered over the genome of the virus, with nine substitutions in

ORFlab, ORF8 (4 substitutions), the spike gene (3 substitutions), and ORF7a (single

substitution) (4). Notably, the same nonsynonymous changes were found in a familial

cluster, indicating that the viral evolution happened during person-to-person

transmission (4, 47). Such adaptive evolution events are frequent and constitute a

constantly ongoing process once the virus spreads among new hosts (47). Even

though no functional changes occur in the virus associated with this adaptive

evolution, close monitoring of the viral absence of this protein IS related to the

altered virulence of coronaviruses due to changes in morphology and tropism (54).

The E protein consists of three domains, namely, a short hydrophilic amino terminal,

a large hydrophobic transmembrane domain, and an efficient C-terminal domain (51).

The SARS-CoV-2 E protein reveals a similar amino acid constitution without any

substitution (16)