Linkage-Specific Conformational Ensembles of Non-Canonical Polyubiquitin Chains

Published

February 28, 2016

Author(s)

Carlos A. Castaneda, Apurva Chaturvedi, Christina M. Camara, Joseph E. Curtis, Susan T. Krueger, David Fushman

Abstract

Polyubiquitination is a critical protein post-translational modification involved in a variety of processes in eukaryotic cells. The molecular basis for selective recognition of the polyubiquitin signals by cellular receptors is determined by the conformations polyubiquitin signals by cellular receptors is determined by the conformations polyubiquitin chains adopt; this has been demonstrated for K48- and K63-linked chains. Recent studies of the so-called non-canonical chains (linked via K6, K11, K27, K29, or K33) suggest they plan important regulatory roles in growth, development, and immune system pathways, but biophysical studies are needed to elucidate the physical/structural basis of their interactions with receptors. A first step towards this goal is characterization of the conformations these chains adopt in solution. We assembled diubiquitins (Ub₂) comprised of every lysine linkage. Using solution NMR measurements, small-angle neutron scattering (SANS), and in silico ensemble generation, we determined population-weighted conformational ensembles that shed light on the structure and dynamics of the non-canonical polyubiquitin chains. We found that polyubiquitin is conformationally heterogeneous, and each chain type exhibits unique conformational ensembles. For example, K6-Ub₂ and K11-Ub₂ (at physiological salt concentration) are in dynamic equilibrium between at least two conformers, where one exhibits a unique Ub/Ub interface, distinct from that observed in K48-Ub₂ but similar to crystal structures of these chains. Conformers for K29-Ub_{2 and K33-Ub}d2^ resemble recent crystal structures in the ligandbound state. Remarkably, a number of diubiquitins adopt conforms similar to K48-Ub₂ and K63-Ub₂, suggesting potential overlap of biological function among different lysine linkages. These studies highlight the potential power of determining function from elucidation of conformational states.

Citation

Physical Chemistry Chemical Physics

Volume

18

Issue

8

Pub Type

Journals

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Keywords

non-canonical polyubiquitin chains, residual dipolar couplings, small-angle neutron scattering, sparse ensemble selection, conformational ensemble

Citation

Castaneda, C. , Chaturvedi, A. , Camara, C. , Curtis, J. , Krueger, S. and Fushman, D. (2016), Linkage-Specific Conformational Ensembles of Non-Canonical Polyubiquitin Chains, Physical Chemistry Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919200 (Accessed May 3, 2024)