Porcine aminopeptidase N
Porcine aminopeptidase N (pAPN), a protein of 963 aa widely distributed
in the small intestine and kidney of pigs, can be decomposed into 2
subunits by trypsin, a 95 kDa of N-terminal and a 50 kDa of C- terminus,
while the positions of 717-813aa contain 3 antigen neutralizing sites.
The functions or roles of pAPN in the pathogenic mechanisms of PEDV or
TGEV infection have been extensively studied in recent years. Through
screening and identification, the main antigen functional regions of
pAPN are determined to be located at the positions of 36-153aa,
349-591aa and 592-963aa, respectively (Bo-qi, Guang-xing, & Xiao-feng,
2009). Although the conclusion of the receptor role for pAPN in PEDV
infection remains elusive, this suggestion has been supported by the
facts that pAPN can bind to the S1 region of the S PEDV protein (BX, JW,
& YJ, 2007), and the ST cells efficiently expressing pAPN through gene
recombination can support the PEDV infection and proliferation, which
also is closely associated with the distributed density of pAPN (N. E &
C, 2010). However, other studies indicated that the presence of pAPN
does not render Vero cells susceptible to PEDV infection (JS, DS, & BK,
2003) and the capability of pAPN to enhance the infectivity of PEDV is
related to its aminopeptidase activity rather than its receptor role (S.
K et al., 2016). Whether this discrepancy is only due to various cell
lines used in these studies since the results obtained in ST cells can
not be replicated in Hela cells, or whether the existence of other
routes of PEDV infection results in variable consequences, remains to be
further classified.