Structure of archaeal translational initiation factor 2 betagamma-GDP reveals significant conformational change of the beta-subunit and switch 1 region.
Archaeal/eukaryotic initiation factor 2 (a/eIF2) consists of alpha-, beta-, and gamma-subunits and delivers initiator methionine tRNA (Met-tRNA(i)) to a small ribosomal subunit in a GTP-dependent manner. The structures of the aIF2betagamma (archaeal initiation factor 2 betagamma) heterodimeric complex in the apo and GDP forms were analyzed at 2.8- and 3.4-A resolution, respectively. The results showed that the N-terminal helix and the central helix-turn-helix domain of the beta-subunit bind to the G domain of the gamma-subunit but are distant from domains 2 and 3, to which the alpha-subunit and Met-tRNA(i) bind. This result is consistent with most of the previous analyses of eukaryotic factors, and thus indicates that the binding mode is essentially conserved among a/eIF2. Comparison with the uncomplexed structure showed significant differences between the two forms of the beta-subunit, particularly the C-terminal zinc-binding domain, which does not interact with the gamma-subunit and was suggested previously to be involved in GTP hydrolysis. Furthermore, the switch 1 region in the gamma-subunit, which is shown to be responsible for Met-tRNA(i) binding by mutational analysis, is moved away from the nucleotide through the interaction with highly conserved R87 in the beta-subunit. These results implicate that conformational change of the beta-subunit facilitates GTP hydrolysis by inducing the conformational change of the switch 1 region toward the off state.
Sokabe
Masaaki
M
Faculty of Advanced Life Sciences, Hokkaido University, Sapporo 060-0810, Japan.
Yao
Min
M
Sakai
Naoki
N
Toya
Shingo
S
Tanaka
Isao
I
D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D006153:Guanosine Diphosphate / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010448:Peptide Initiation Factors / Q000737:chemistry*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry*; D020027:Pyrococcus furiosus / Q000737:chemistry*; D012358:RNA, Transfer, Met / Q000737:chemistry; D016415:Sequence Alignment
D019843:Archaeal Proteins; D010448:Peptide Initiation Factors; D021122:Protein Subunits; D012358:RNA, Transfer, Met; C116557:initiation factor 2, archaeal; D006153:Guanosine Diphosphate