Calcium Sensitive Allostery Regulates the PI(4,5)P2 Binding Site of the Dysferlin C2A Domain

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Abstract
C2 domains are the second-most abundant calcium binding module in the proteome. Activity of the muscular dystrophy associated protein dysferlin is dependent on the C2A domain at the N-terminus of the protein, which couples calcium and PI(4,5)P2 binding through an unknown mechanism. Using solution state nuclear magnetic resonance spectroscopy we confirm the phosphoinositide binding site for the domain and find that calcium binding attenuates millisecond to microsecond motions at both in the calcium binding loops and the concave face of the C2A, including a portion of the phosphoinositide binding site. Our results support a model whereby increasing calcium concentrations shift the phosphoinositide binding pocket of C2A into a binding-competent state, allowing for calcium dependent membrane targeting. This model contrasts with the canonical mechanism for C2 domain-phosphoinositide interaction and provides a basis for how pathogenic mutations in the C2A domain result in loss of function and disease.

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