Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 39, Pages 15662-15667Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1309360110
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Funding
- National Institutes of Health (NIH) [GM022778, NIH 5 T32 GM 8283-25]
- European Research Council
- French Infrastructure for Integrated Structural Biology [ANR-10-INSB-05-01]
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The initiation of protein synthesis uses initiation factor 2 (IF2) in prokaryotes and a related protein named eukaryotic initiation factor 5B (eIF5B) in eukaryotes. IF2 is a GTPase that positions the initiator tRNA on the 30S ribosomal initiation complex and stimulates its assembly to the 50S ribosomal subunit to make the 70S ribosome. The 3.1-angstrom resolution X-ray crystal structures of the full-length Thermus thermophilus apo IF2 and its complex with GDP presented here exhibit two different conformations (all of its domains except C2 domain are visible). Unlike all other translational GTPases, IF2 does not have an effecter domain that stably contacts the switch II region of the GTPase domain. The domain organization of IF2 is inconsistent with the articulated lever mechanism of communication between the GTPase and initiator tRNA binding domains that has been proposed for eIF5B. Previous cryo-electron microscopy reconstructions, NMR experiments, and this structure show that IF2 transitions from being flexible in solution to an extended conformation when interacting with ribosomal complexes.
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