Structural basis for high-affinity actin binding revealed by a β-III-spectrin SCA5 missense mutation

Adam W. Avery, Michael E. Fealey, Fengbin Wang, Albina Orlova, Andrew R. Thompson, David D. Thomas, Thomas S. Hays, Edward H. Egelman

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Abstract

Spinocerebellar ataxia type 5 (SCA5) is a neurodegenerative disease caused by mutations in the cytoskeletal protein β-III-spectrin. Previously, a SCA5 mutation resulting in a leucine-to-proline substitution (L253P) in the actin-binding domain (ABD) was shown to cause a 1000-fold increase in actin-binding affinity. However, the structural basis for this increase is unknown. Here, we report a 6.9 Å cryo-EM structure of F-actin complexed with the L253P ABD. This structure, along with co-sedimentation and pulsed-EPR measurements, demonstrates that high-affinity binding caused by the CH2-localized mutation is due to opening of the two CH domains. This enables CH1 to bind actin aided by an unstructured N-terminal region that becomes α-helical upon binding. This helix is required for association with actin as truncation eliminates binding. Collectively, these results shed light on the mechanism by which β-III-spectrin, and likely similar actin-binding proteins, interact with actin, and how this mechanism can be perturbed to cause disease.

Original languageEnglish (US)
Article number1350
JournalNature communications
Volume8
Issue number1
DOIs
StatePublished - Dec 1 2017

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