The S protein of PEDV
This S gene encoded spike (S)
protein is a type I glycoprotein, while three S proteins of PEDV forming
a rod-shaped functional spike trimer located in the outermost layer of
virus particles, are the foundation for its multi-function, such as the
binding of PEDV to other molecules, the entry of virus into target cells
(L. C et al., 2015; F. F et al., 2017). Based on the homology analysis
of its counterparts of other coronaviruses, the S protein of PEDV can be
divided into two parts: S1 (1-789 aa) and S2 (790-1383 aa). The function
of the S1 protein is to mediate the viruses to adsorb the viral
receptors on the host cells, while the role of the S2 is to induce
membrane fusion, thereby facilitating the viruses to invade the host
cells (Wrapp D & JS, 2019; L. F, 2012, 2015). Moreover, the binding of
the S1 with receptors on the host cell surface can incur the
conformation change and fusion of the S2 with the cell membrane. Indeed,
previous results have confirmed the interaction of the S protein with
the target cell surface receptor(s), which is mediated by the S1 domain
NTD (L. C et al., 2015; D. F et al., 2016). Besides these, the
involvement of the S protein in trypsin-dependent PEDV propagation in
cultured cells has been suggested (L. W, FJM, Q, PJM, & BJ, 2016). This
effect of the S protein is considered to be exerted by proteolytic
activation by trypsin or other proteases following its binding to
receptor(s) (L. C et al., 2016; O et al., 2014), which is necessary for
the membrane fusion, formation of syncytium, cell entry of the virus,
thereby enhancing infectivity of PEDV (JE, DJ, & HJ, 2011). This is
also supported by the S protein mutations influencing the proteolytic
cleave of it (L. W et al., 2015; K. Y, C, V, RA, & KO, 2017).
Additionally, a determinant role for the S protein in efficient viral
release from target cells has also been proposed, while compelling
evidence are required to substantiate this concept (O et al., 2014). It
becomes clear that the receptor binding capability and the role in viral
entry allow the S protein to determine PEDV invasion and release, tissue
tropism, host range and cross-species transmission, even to affect
trypsin-dependent PEDV proliferation (L. C et al., 2016; O et al., 2014;
L. W et al., 2015). Therefore, the property of the S gene prone to
mutation often leads to pathogenic alterations of this virus (C. F et
al., 2015; H. Y et al., 2017). The S protein contains a variety of
antigenic epitopes and plays an important role in inducing the body to
produce neutralizing antibodies (Song D & B, 2012). In view of this
vital role of the S protein, it is widely used for the development of
PEDV subunit vaccine, genetic engineering vaccine and PEDV antibody
detection kit (CY et al., 2019; L. H et al., 2018).