Abstract

Interferon-induced protein kinase (PKR) is a member of a family of kinases that regulate translation initiation through phosphorylation of eukaryotic initiation factor 2alpha. In addition to the conserved catalytic subdomains that are present in all serine/threonine kinases, the eukaryotic initiation factor 2alpha kinases possess an insert region between catalytic subdomains IV and V that has been termed the kinase insert domain. To investigate the importance of the kinase insert domain of PKR, several deletions and point mutations were introduced within this domain and analyzed for kinase activity both in vitro and in vivo. Here we show that deletion of the kinase insert sequence or mutation of serine 355, which lies within this region, abrogates kinase activity. In addition, the kinase insert domain of PKR and adjacent amino acids (LFIQME) in catalytic subdomain V are not required for binding of the pseudosubstrate inhibitor K3L from vaccinia virus. A portion of the catalytic domain of PKR between amino acids 366 and 415 confers K3L binding in vivo, suggesting a possible role for this region of PKR in substrate interaction.

Highlights

  • The double-stranded RNA1-activated protein kinase, PKR is an interferon-inducible protein that plays a key role in the antiviral and antiproliferative interferon response

  • Our findings indicate that the kinase insert domain is dispensible for K3L interaction, but it is required for kinase activity, suggesting that the kinase insert domain is not involved in binding of K3L

  • In this study we report that the kinase insert domain of human PKR is required for kinase activity but does not play a role in binding of PKR to the pseudosubstrate K3L protein from vaccinia virus

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Summary

Introduction

The double-stranded RNA (dsRNA)1-activated protein kinase, PKR ( called p68, DAI, and P1 kinase) is an interferon-inducible protein that plays a key role in the antiviral and antiproliferative interferon response (for a review see Ref. 1). Prior to the association of the 60 S ribosomal subunit, GTP hydrolysis results in formation of an inactive eIF21⁄7GDP complex. PKR mutants cause the malignant transformation of cells possibly through formation of inactive heterodimers with endogenous PKR [18], diminishing the levels of eIF2␣ phosphorylation. In support of this hypothesis, a recent study has shown that expression of the eIF2␣ subunit, in which the phosphorylation site residue (serine 51) was mutated to alanine, resulted in malignant transformation of NIH 3T3 cells [19]

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