Heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1)
Heterogeneous nuclear ribonucleoprotein (hnRNP) is a general term
designated for the members of the RNA binding protein family, which
consists of at least twenty members, referred as to from A to U, with
molecular weight ranging from 34kDa to 120kDa. HnRNPA1, one of the most
abundant members of this family (CK et al., 2017), can be divided into
two different parts: the N-terminal functional region with two closely
linked RNA recognition motifs mainly responsible for binding to RNA, and
the C-terminal glycine enrichment region with RNA binding sites and
localization sequence M9 principally involved in RNA binding, cell
localization and protein-protein interaction (U & H, 2013). As a
multifunctional protein, HnRNPA1 widely participates in the regulation
of RNA transcription, splicing, nuclear shuttle and the translation of
cellular and viral proteins. Similarly, the N protein, as an RNA binding
protein, is implicated in forming the replication and transcription
complex of coronaviruses, and plays a crucial role in the replication of
viruses. Especially, the binding of hnRNPA1 to the N proteins of other
coronaviruses like MHV and SARS-CoV, has been confirmed by a series of
experiments (W. Y & X, 1999). Likewise, the binding and co-localization
of hnRNPA1 with the N protein of PEDV have been verified, implying the
involvement of hnRNPA1 in the formation of PEDV
replication-transcription complex (L. Z et al., 2018). It remains to be
determined whether the same binding site of the PEDV N protein is used
to interact with hnRNPA1 as that of other coronaviruses such as MHV and
SARS-CoV [75, 76].
Assembly and release
Successful PEDV replication requires the coordinated production,
processing and assembly of each protein and nucleic acid of the virus,
as well as the release of progeny viruses capable of infecting new cells
from infected cells. Initially, the interaction of the same type M
proteins provides a scaffold for the morphogenesis of the virus, while
the interaction between the M-S and M-N facilitates the recruitment of
the structural components of the virus to the assembly site (Y. Y & BG,
2007). Finally, the newly generated virus particles are transported in
the smooth vesicles and released by the exocytic pathway of exocytosis.
In this aspect, multiple host factors also take part in these processes
of coronavirus including PEDV.