Large-scale opening of utrophin's tandem calponin homology (CH) domains upon actin binding by an induced-fit mechanism

Ava Y. Lin, Ewa Prochniewicz, Zachary M. James, Bengt Svensson, David D. Thomas

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

We have used site-directed spin labeling and pulsed electron paramagnetic resonance to resolve a controversy concerning the structure of the utrophin-actin complex, with implications for the pathophysiology of muscular dystrophy. Utrophin is a homolog of dystrophin, the defective protein in Duchenne and Becker muscular dystrophies, and therapeutic utrophin derivatives are currently being developed. Both proteins have a pair of N-terminal calponin homology (CH) domains that are important for actin binding. Although there is a crystal structure of the utrophin actin-binding domain, electron microscopy of the actin-bound complexes has produced two very different structural models, in which the CH domains are in open or closed conformations. We engineered a pair of labeling sites in the CH domains of utrophin and used dipolar electron-electron resonance to determine the distribution of interdomain distances with high resolution. We found that the two domains are flexibly connected in solution, indicating a dynamic equilibrium between two distinct open structures. Upon actin binding, the two domains become dramatically separated and ordered, indicating a transition to a single open and extended conformation. There is no trace of this open conformation of utrophin in the absence of actin, providing strong support for an induced-fit model of actin binding.

Original languageEnglish (US)
Pages (from-to)12729-12733
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume108
Issue number31
DOIs
StatePublished - Aug 2 2011

Keywords

  • Cryo-EM
  • Pulsed EPR
  • Spectroscopy

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