Single-particle EM reveals extensive conformational variability of the Ltn1 E3 ligase

Proc Natl Acad Sci U S A. 2013 Jan 29;110(5):1702-7. doi: 10.1073/pnas.1210041110. Epub 2013 Jan 14.


Ltn1 is a 180-kDa E3 ubiquitin ligase that associates with ribosomes and marks certain aberrant, translationally arrested nascent polypeptide chains for proteasomal degradation. In addition to its evolutionarily conserved large size, Ltn1 is characterized by the presence of a conserved N terminus, HEAT/ARM repeats predicted to comprise the majority of the protein, and a C-terminal catalytic RING domain, although the protein's exact structure is unknown. We used numerous single-particle EM strategies to characterize Ltn1's structure based on negative stain and vitreous ice data. Two-dimensional classifications and subsequent 3D reconstructions of electron density maps show that Ltn1 has an elongated form and presents a continuum of conformational states about two flexible hinge regions, whereas its overall architecture is reminiscent of multisubunit cullin-RING ubiquitin ligase complexes. We propose a model of Ltn1 function based on its conformational variability and flexibility that describes how these features may play a role in cotranslational protein quality control.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier Proteins / chemistry
  • Carrier Proteins / metabolism
  • Carrier Proteins / ultrastructure
  • Cullin Proteins / chemistry
  • Cullin Proteins / metabolism
  • Cullin Proteins / ultrastructure
  • Humans
  • Imaging, Three-Dimensional
  • Microscopy, Electron / methods*
  • Models, Molecular
  • Particle Size
  • Protein Binding
  • Protein Conformation*
  • Protein Structure, Tertiary
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Saccharomyces cerevisiae Proteins / ultrastructure*
  • Ubiquitin / chemistry
  • Ubiquitin / metabolism
  • Ubiquitin / ultrastructure
  • Ubiquitin-Protein Ligases / chemistry*
  • Ubiquitin-Protein Ligases / metabolism
  • Ubiquitin-Protein Ligases / ultrastructure*


  • Carrier Proteins
  • Cullin 1
  • Cullin Proteins
  • RBX1 protein, human
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin
  • Ltn1 protein, S cerevisiae
  • Ubiquitin-Protein Ligases