Title
Structural basis for high-affinity actin binding revealed by a β-III-spectrin SCA5 missense mutation
Author
Adam W. Avery, Michael E. Fealey, Fengbin Wang, Albina Orlova, Andrew R. Thompson, David D. Thomas, Thomas S. Hays, Edward H. Egelman
Year
2017
Journal
Nature Communications
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.
Full Article
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Protein folding, Thermal stability, Thermodynamics, Biochemistry