Conformational transition of initiation factor 2 from the GTP- to GDP-bound state visualized on the ribosome

• Published in: Nature structural & molecular biology Vol. 12; no. 12; pp. 1145 - 1149
• Main Authors: Klaholz, Bruno P, Myasnikov, Alexander G, Marzi, Stefano, Simonetti, Angelita, Giuliodori, Anna Maria, Gualerzi, Claudio O, Yusupova, Gulnara, Yusupov, Marat
• Format: Journal Article
• Language: English
• Published: United States Nature Publishing Group 01.12.2005
• Subjects: Binding sites; Biochemistry, Molecular Biology; Biology; Cryoelectron Microscopy; Guanosine Diphosphate - chemistry; Guanosine Triphosphate - chemistry; Hydrolysis; Life Sciences; Physiological aspects; Prokaryotes; Prokaryotic Initiation Factor-2 - chemistry; Protein Biosynthesis; Protein Conformation; Protein synthesis; Proteins; Ribonucleic acid; Ribosomes; Ribosomes - chemistry; RNA; RNA, Messenger - chemistry; RNA, Transfer, Met - chemistry; Structure; Thermus thermophilus; Transfer RNA; France
• ISSN: 1545-9993; 1545-9985
• DOI: 10.1038/nsmb1012

Initiation of protein synthesis is a universally conserved event that requires initiation factors IF1, IF2 and IF3 in prokaryotes. IF2 is a GTPase essential for binding initiator transfer RNA to the 30S ribosomal subunit and recruiting the 50S subunit into the 70S initiation complex. We present two cryo-EM structures of the assembled 70S initiation complex comprising mRNA, fMet-tRNA(fMet) and IF2 with either a non-hydrolyzable GTP analog or GDP. Transition from the GTP-bound to the GDP-bound state involves substantial conformational changes of IF2 and of the entire ribosome. In the GTP analog-bound state, IF2 interacts mostly with the 30S subunit and extends to the initiator tRNA in the peptidyl (P) site, whereas in the GDP-bound state IF2 steps back and adopts a 'ready-to-leave' conformation. Our data also provide insights into the molecular mechanism guiding release of IF1 and IF3.