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BIOLOGICAL SCIENCES / BIOCHEMISTRY
Structure of archaeal translational initiation factor 2 
–GDP reveals significant conformational change of the -subunit and switch 1 region
*Faculty of Advanced Life Sciences, Hokkaido University, Sapporo 060-0810, Japan; and RIKEN Harima Institute/SPring-8, Hyogo 679-5148, Japan
Edited by Peter B. Moore, Yale University, New Haven, CT, and approved July 10, 2006 (received for review May 19, 2006)
Archaeal/eukaryotic initiation factor 2 (a/eIF2) consists of 
-, 
-, and 
-subunits and delivers initiator methionine tRNA (Met-tRNAi) to a small ribosomal subunit in a GTP-dependent manner. The structures of the aIF2 (archaeal initiation factor 2 ) heterodimeric complex in the apo and GDP forms were analyzed at 2.8- and 3.4-Å resolution, respectively. The results showed that the N-terminal helix and the central helix–turn–helix domain of the -subunit bind to the G domain of the -subunit but are distant from domains 2 and 3, to which the -subunit and Met-tRNAi 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 -subunit, particularly the C-terminal zinc-binding domain, which does not interact with the -subunit and was suggested previously to be involved in GTP hydrolysis. Furthermore, the switch 1 region in the -subunit, which is shown to be responsible for Met-tRNAi binding by mutational analysis, is moved away from the nucleotide through the interaction with highly conserved R87 in the -subunit. These results implicate that conformational change of the -subunit facilitates GTP hydrolysis by inducing the conformational change of the switch 1 region toward the off state.
initiator methionine tRNA | ribosome
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, www.pdb.org (PDB ID codes 2D74 and 2DCU).
To whom correspondence should be addressed. E-mail: tanaka{at}castor.sci.hokudai.ac.jp
© 2006 by The National Academy of Sciences of the USA
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