Sialic acid
It is recognized that a large number of the main receptors for many
viruses belong to glycoprotein or glycolipid, with sialic acid or sialic
acid derivatives at the end, such as those of pathogenic influenza A, B,
C and parainfluenza virus (S. H et al., 2016). In this regard, the
ability of PEDV binding to sialic acid, such as carbohydrates (Neu5Ac)
and proteins especially glycoproteins or glycolipid molecules located at
the cell surface, has also been confirmed in previous studies (K. F &
G, 1993; P. G et al., 2012). Moreover, using glycoproteins as receptors
is important strategy for viral intestinal pathogenicity because the
properties of glycoproteins facilitate viral binding to mucin on the
surface of epithelial cells in animal viscera (W. Jh, 2002). The effort
of Daniel Wrapp et al. to parse the prefusion conformation of the PEDV S
protein using cryo-electron microscopy at a resolution of 3.1 Å revealed
the presence of the sialic acid-binding domain at the N terminal of the
S1 subunit (Wrapp D & JS, 2019). Recognition of sugars as co-receptors
for PEDV appears to be a strategy for adapting organisms to this class
of diarrhea-causing viruses, suggesting that the binding of PEDV to
sialic acid facilitates to survive in adverse intestinal conditions.
Further in-depth investigation indicated that the S1-434, S253-533
fragments of PEDV weakly while the S19-638 fragment strongly binds to
the pAPN expressing cells, suggesting the occurrence of recognition of
pAPN as a receptor by the C-terminal region of the PEDV S1 protein and
the capability of recognition of other cellular molecules like sugars by
the N-terminal region of the S1 subunit (D. F et al., 2016). Thus, PEDV
may use sugars as receptors or co-receptors, as similar to TGEV using
Neu5Gc and Neu5Ac as co-receptors (P, CF, & S, 2006). The next works
focusing on what exact sugar molecules are utilized by PEDV as
co-receptors are of significance.