Structural dynamics of bacterial translation initiation factor IF2.

Bacterial translation initiation factor IF2 promotes ribosomal subunit association, recruitment and binding of fMet-tRNA to the ribosomal P-site, and initiation dipeptide formation. Here we present the solution structures of GDP-bound and apo-IF2-G2 of Bacillus stearothermophilus and provide evidence that this isolated domain binds the 50S ribosomal subunit and hydrolyzes GTP. Differences between the free and GDP-bound structures of IF2-G2 suggest that domain reorganization within the G2-G3-C1 regions underlies the different structural requirements of IF2 during the initiation process. However, these structural signals are unlikely forwarded from IF2-G2 to the C-terminal fMet-tRNA binding domain (IF2-C2) because the connected IF2-C1 and IF2-C2 modules show completely independent mobility, indicating that the bacterial inter-domain connector lacks the rigidity that was found in the archaeal IF2- homolog aIF5B.