PKR and eIF2alpha: integration of kinase dimerization, activation, and substrate docking.

Area of Science:

• Molecular Biology
• Virology
• Structural Biology

Background:

• The RNA-dependent protein kinase (PKR) is a crucial antiviral factor that inhibits protein synthesis upon detecting viral double-stranded RNA.
• PKR phosphorylates the alpha subunit of the translation initiation factor eIF2 (eIF2alpha), a key step in halting cellular protein production during viral infection.

Purpose of the Study:

• To elucidate the structural mechanisms underlying the interaction between PKR and its substrate, eIF2alpha.
• To understand how PKR dimer formation contributes to its kinase activation and substrate recognition.

Main Methods:

• X-ray crystallography was used to determine the structures of eIF2alpha bound to PKR.
• Site-directed mutagenesis was employed to analyze the functional importance of specific interfaces within PKR.

Main Results:

• The structures reveal that PKR forms a dimer, with the dimerization interface being critical for kinase activation.
• Detailed insights into how the protein substrate eIF2alpha docks onto the activated PKR kinase.
• Demonstration of allosteric coupling between the dimerization interface and the substrate recognition interface via phosphorylation of the activation loop.

Conclusions:

• The structural and mutagenesis data provide a comprehensive understanding of PKR activation and substrate binding.
• These findings illuminate a key molecular mechanism of the innate antiviral immune response mediated by PKR.
• The study reveals how allosteric regulation through phosphorylation controls kinase activity and substrate interaction.