A ratchet-like inter-subunit reorganization of the ribosome during translocation.
The ribosome is a macromolecular assembly that is responsible for protein biosynthesis following genetic instructions in all organisms. It is composed of two unequal subunits: the smaller subunit binds messenger RNA and the anticodon end of transfer RNAs, and helps to decode the mRNA; and the larger subunit interacts with the amino-acid-carrying end of tRNAs and catalyses the formation of the peptide bonds. After peptide-bond formation, elongation factor G (EF-G) binds to the ribosome, triggering the translocation of peptidyl-tRNA from its aminoacyl site to the peptidyl site, and movement of mRNA by one codon. Here we analyse three-dimensional cryo-electron microscopy maps of the Escherichia coli 70S ribosome in various functional states, and show that both EF-G binding and subsequent GTP hydrolysis lead to ratchet-like rotations of the small 30S subunit relative to the large 50S subunit. Furthermore, our finding indicates a two-step mechanism of translocation: first, relative rotation of the subunits and opening of the mRNA channel following binding of GTP to EF-G; and second, advance of the mRNA/(tRNA)2 complex in the direction of the rotation of the 30S subunit, following GTP hydrolysis.
Frank
J
J
Howard Hughes Medical Institute, Health Research Incorporated at the Wadsworth Center, and Department of Biomedical Sciences, State University of New York at Albany, 12201-0509, USA.
Agrawal
R K
RK
D001692:Biological Transport; D020285:Cryoelectron Microscopy; D004926:Escherichia coli; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D046911:Macromolecular Substances; D008958:Models, Molecular; D008968:Molecular Conformation; D020653:Peptide Elongation Factor G / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*
D046911:Macromolecular Substances; D020653:Peptide Elongation Factor G; D012333:RNA, Messenger; D006160:Guanosine Triphosphate; D012343:RNA, Transfer