PKR kinase domain- eIF2alpha- AMP-PNP complex.
[IF2A_YEAST] eIF-2 functions in the early steps of protein synthesis by forming a ternary complex with GTP and initiator tRNA. This complex binds to a 40S ribosomal subunit, followed by mRNA binding to form a 43S preinitiation complex. Junction of the 60S ribosomal subunit to form the 80S initiation complex is preceded by hydrolysis of the GTP bound to eIF-2 and release of an eIF-2-GDP binary complex. In order for eIF-2 to recycle and catalyze another round of initiation, the GDP bound to eIF-2 must exchange with GTP by way of a reaction catalyzed by eIF-2B. [E2AK2_HUMAN] Following activation by double-stranded RNA in the presence of ATP, the kinase becomes autophosphorylated and can catalyze the phosphorylation of the translation initiation factor EIF2S1, which leads to an inhibition of the initiation of protein synthesis. Double-stranded RNA is generated during the course of a viral infection. In addition to serine/threonine-protein kinase activity, also has tyrosine-protein kinase activity: phosphorylates CDK1 upon DNA damage. CDK1 phosphorylation triggers CDK1 polyubiquitination and subsequent proteolysis, thus leading to G2 arrest.
Publication Abstract from PubMed
In response to binding viral double-stranded RNA byproducts within a cell, the RNA-dependent protein kinase PKR phosphorylates the alpha subunit of the translation initiation factor eIF2 on a regulatory site, Ser51. This triggers the general shutdown of protein synthesis and inhibition of viral propagation. To understand the basis for substrate recognition by and the regulation of PKR, we determined X-ray crystal structures of the catalytic domain of PKR in complex with eIF2alpha. The structures reveal that eIF2alpha binds to the C-terminal catalytic lobe while catalytic-domain dimerization is mediated by the N-terminal lobe. In addition to inducing a local unfolding of the Ser51 acceptor site in eIF2alpha, its mode of binding to PKR affords the Ser51 site full access to the catalytic cleft of PKR. The generality and implications of the structural mechanisms uncovered for PKR to the larger family of four human eIF2alpha protein kinases are discussed.
Higher-order substrate recognition of eIF2alpha by the RNA-dependent protein kinase PKR.,Dar AC, Dever TE, Sicheri F Cell. 2005 Sep 23;122(6):887-900. PMID:16179258
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.