From the structural protein of
coronavirus the spiked glycoprotein play very essential role in the
entry of the corona virus in to the host cells. The name of coronavirus
also related by its S-protein have a crown appearance which is derived
their name; corona in Latin means crowns. The spiked protein has the
receptor-binding domain (RBD). Thus, the virus use S-protein to bind its
receptor with host cells by its S1 subunit followed by fused the viral
and hast cell membrane through its S2 subunits.30,31S-proteins coronavirus are the large heavily N-glycosylated proteins
which mediate the interaction of the virus with the host cell surface
receptors.30,32 Angiotensin-converting enzyme 2 (ACE2)
is an entry receptor on human for SARS-CoV-2 and
SARS-CoV-113,18,33-35 Angiotensin-converting enzyme 2
(ACE2) is an enzyme found in the outer surface cells such as nasal
mucosa, nasopharynx, lung, stomach, small intestine, colon, skin, lymph
nodes, thymus, bone marrow, spleen, liver, kidney, and brain. ACE2
regulates the renin-angiotensin system, which has an important role on
regulation of blood pressure and heart
functions.30,35-37
The genomic sequence result of (COVID-19) SARS-CoV-2 has shown 79.6%
identical with SARS-CoV-1 and 96% with bat coronavirus
respectively.38 Furthermore, in vitro based recent
experimental study using the ACE recombinant protein and ACE2 expressing
cell lines indicated that the SARS-CoV-2 and SARS-CoV-1 showed the
similar binding affinity to the host ACE2 receptor.18
S-protein has very essential role to produce a potentially effective
antibody and vaccine. Recently the receptor-biding domain (RBM) in the
S-protein apparently amino acid residue (Gln493) provide favorable
interactions with human ACE2, which enabled the virus for human cell
infections. This might be related the infectivity potential of the
COVID-19.39 The amino acid sequence result analysis of
SARS-CoV and SARS-CoV-2 SAR showed that similarity 75% in S-protein,
73.7% in receptor-biding domain (RBM) and 50% receptor binding motif
(RBM).18
Since the COVID-19 (SARS-CoV-2) and SARS-CoV-1 showed sequence
similarity, identify the common cross-reactive epitopes (CREs) is the
key point. The shared CREs are similar epitope regions on the antigen
surface among viruses that can be bound or neutralized by the same
antibodies. Interestingly, very similar epitope was identified in
between COVID-19 and SARS-CoV-1 at the biding site of S-protein with
human ACE2 receptor.39 Recently, robust anti-ACE-2
Blocking antibody showed limited binding and neutralization activity
against SARS-CoV-1. However, anti-ACE2 nonbanking SARS CoV-1 antibody
showed positive cross-neutralizing activities to SARS-CoV-2. Indeed the
reason is unknown yet. 18 This might be due to the RBD
conserved immunogenic part that antibody able to recognize in SARS-CoV-1
and the SARS-CoV-2. This provides a scientific evidence to develop a
potent antibody or vaccine based on RBD against COVID-19.
Figure 2. ABO blood group. a phenotypic distribution of ABO
blood group by race and Ethnicity,29 bRelationship between the ABO Blood Group and the COVID-19
Susceptibility.12
Histo‐blood group antigens which are responsible for ABO blood group are
highly expressed on epithelial cells and many other normal
cells.40 In the same fashion, epithelial cells of
respiratory and digestive tracts are the main site for replication of
SARS-CoV-2 and SARS-CoV-1.6,37 Thus, SARS-CoV can
produce the ABH carbohydrate epitope in the epithelia cells. S-protein
of virions produced by either A or B individuals could be decorated with
A or B carbohydrate epitopes, respectively. Naturally, with unknown
reason we huma acquired natural anti-histo-blood group antibodies. These
natural antibodies from blood group O, B, and A individuals could bind
to the S-protein and block its interaction with ACE2. Surprisingly, O
blood group individual showed very low risk of infection by COVID-19 and
SARS-CoV-1 as compared with non O blood group.12,28,41The major reason is that the O blood group individuals have anti-A and
anti-B antibodies in plasma. Interestingly, the plasma contained high
anti-A antibody titer able to inhibit the S-protein interacting with
ACE2 receptors.13 This indicated that ABO polymorphism
has significant effect of the SARS-CoV outbreak further more study is
needed to produce broadly neutralizing antibody and vaccine.
Green fluorescent tagged the C-terminal of S-protein was expressed in
Chinese hamster ovary cells cotransfected with an
α1,2-fucosyltransferase and an A-transferase (antigen A) in order to
coexpress the S-glycoprotein ectodomain. The vitro result showed that
anti-A monoclonal antibody and anti-A natural antibody from O blood
group inhibited ACE2 and S-protein of SARS-CoV-1
interaction.13,42 Furthermore, convalescent plasma
therapy taken from O blood group result in better recovery including for
pregnant woman.22 In erectly, SARS-CoV-2 S- protein
peptide are identified in human leukocyte antigen (HLA) complexes. The
protein glycosylation has role in the adaptive immune response; this
could leads for development of potential antibody and
vaccine.43 Therefore, furthermore studies based on
these evidence are suggested.
The potential of natural antibody in human varies from person to person.
The natural antibodies possibly decrease over years in developed
countries due to good environmental and person hygiene. Peoples who
lived in less developed countries may elicit good natural antibodies.
Plasma taken from O blood group with high anti-A antibody dramatically
inhibits the interaction of S-protein with ACE2. However, Plasma from O
blood group with low anti-A antibody did not inhibit S-protein and ACE2
in cell adhesion assay.13 ABO blood group based
intervention of the COVID-19 may slowdown the fast spread the outbreak.
Moreover, antigen-A based further study could lead to get potent
antibody and vaccine.
Figure 3. SARS-CoV-2 entry to host cell and inhibition by
antibody mechanism. The SARS-CoV-2 attaches by its spiked protein sub
unit 1 (S1) to the host Angiotensin-converting enzyme 2 (ACE2)
receptors. The host natural antibody and lab made and neutralizing
monoclonal antibody can inhibited the interaction of the S-protein and
host ACE2.The membrane fusion is carried out by its S2-proten. The RNA
virus replicate inside the host genome and finally RNA virus released.