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

Dmitry Lyumkis, Selom K. Doamekpor, Mario H. Bengtson, Joong-Won Lee, Tasha B. Toro, Matthew D. Petroski, Christopher D. Lima, Clinton S. Potter, Bridget Carragher and Claudio A. P. Joazeiro
Proceedings of the National Academy of Sciences of the United States of America
Vol. 110, No. 5 (January 29, 2013), pp. 1702-1707
Stable URL: http://www.jstor.org/stable/41992104
Page Count: 6
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Single-particle EM reveals extensive conformational variability of the Ltn1 E3 ligase
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Abstract

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 LtnVs 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.

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