title: Conformational transition of initiation factor 2 from the GTP- to GDP-bound state visualized on the ribosome.
abstract: 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.
authors.affiliation: Department of Structural Biology and Genomics, Institute of Genetics and Molecular and Cellular Biology, Centre National de la Recherche Scientifique/Institut National de la Santé et de la Recherche Médicale, Université Louis Pasteur, Illkirch, France.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Myasnikov
authors.forename: Stefano
authors.initials: S
authors.lastname: Marzi
authors.forename: Angelita
authors.initials: A
authors.lastname: Simonetti
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Giuliodori
authors.forename: Claudio O
authors.initials: CO
authors.lastname: Gualerzi
authors.forename: Gulnara
authors.initials: G
authors.lastname: Yusupova
authors.forename: Marat
authors.initials: M
authors.lastname: Yusupov
authors.forename: Bruno P
authors.initials: BP
authors.lastname: Klaholz
mesh_terms: D020285:Cryoelectron Microscopy; D006153:Guanosine Diphosphate / Q000737:chemistry*; D006160:Guanosine Triphosphate / Q000737:chemistry*; D006868:Hydrolysis; D039881:Prokaryotic Initiation Factor-2 / Q000737:chemistry*; D014176:Protein Biosynthesis; D011487:Protein Conformation; D012333:RNA, Messenger / Q000737:chemistry; D012358:RNA, Transfer, Met / Q000737:chemistry; D012270:Ribosomes / Q000737:chemistry*; D016963:Thermus thermophilus
chemical_list: D039881:Prokaryotic Initiation Factor-2; D012333:RNA, Messenger; D012358:RNA, Transfer, Met; C089238:fMet-tRNA(fMet); D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate