Abstract
PKZ is a novel and unique eIF2α protein kinase identified in fish. Although PKZ is most homologous to PKR, particularly in the C-terminal catalytic domain, it contains two N-terminal Z-DNA-binding domains (Zα1 and Zα2) instead of the dsRNA binding domains (dsRBDs) in PKR. As a novel member of eIF2α kinase family, the available data suggest that PKZ has some distinct mechanisms for recognition, binding, and B-Z DNA transition. Functionally, PKZ seems to be activated by the binding of Zα to Z-DNA and participates in innate immune responses. In this review, we summarize the recent progress on fish PKZ.
Highlights
In eukaryotes, translation initiation is an extremely complicated process, and regulation of mRNA translation is very important for a cell to adapt to various stress conditions
We summarize the recent progress on fish protein kinase containing Z-DNA binding domains (PKZ) and its role in innate immune response
It is likely that the coexistence of double-stranded RNA-dependent protein kinase (PKR) and PKZ is especially important to taxonomically lower fish species that live in a complex water environment, since harboring distinct N-terminal domains enable fish PKR and PKZ to recognize different viral nucleic acids, which makes the fish innate immune system more effective by broadening their ability to sense viruses and to defense against viral infection cooperatively
Summary
Translation initiation is an extremely complicated process, and regulation of mRNA translation is very important for a cell to adapt to various stress conditions. As an important mechanism for control of protein synthesis, phosphorylation, or dephosphorylation of eukaryotic translation initiation factor 2 α subunit (eIF2α) represents a core molecular switch for stress adaptation and rapid metabolic regulation [1]. EIF2α is phosphorylated at Ser by a family of four kinases, HRI (heme-regulated inhibitor), PERK (PKR-like endoplasmic reticulum kinase), GCN2 (general control non-derepressible-2), and PKR (double-stranded RNA-dependent protein kinase). PKR is a well-known dsRNA-activated and interferon (IFN)-stimulated protein, and plays significant roles in antiviral immune response [2,3,4]. PKZ has a closer evolutionary relationship with PKR [14] It protects fish cells against viral infection through phosphorylation of eIF2α and may act as a cytosolic DNA sensor to initiate innate immune response [15].
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