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.
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.
J
J
Frank
R K
RK
Agrawal
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