Crystal structure of the N-terminal segment of human eukaryotic translation initiation factor 2alpha.

Eukaryotic translation initiation factor 2alpha (eIF2alpha) is a member of the eIF2 heterotrimeric complex that binds and delivers Met-tRNA(i)(Met) to the 40 S ribosomal subunit in a GTP-dependent manner. Phosphorylation/dephosphorylation of eIF2alpha at Ser-51 is the major regulator of protein synthesis in eukaryotic cells. Here, we report the first structural analysis on eIF2, the three-dimensional structure of a 22-kDa N-terminal portion of human eIF2alpha by x-ray diffraction at 1.9 A resolution. This structure contains two major domains. The N terminus is a beta-barrel with five antiparallel beta-strands in an oligonucleotide binding domain (OB domain) fold. The phosphorylation site (Ser-51) is on the loop connecting beta3 and beta4 in the OB domain. A helical domain follows the OB domain, and the first helix has extensive interactions, including a disulfide bridge, to fix its orientation with respect to the OB domain. The two domains meet along a negatively charged groove with highly conserved residues, indicating a likely site for protein-protein interaction.