Alternate Splicing of Dysferlin C2A Confers Ca2+-Dependent and Ca2+-Independent Binding for Membrane Repair

• Published in: Structure (London) 2014-01, Vol.22 (1), p.104-115
• Main Authors: Fuson, Kerry, Rice, Anne, Mahling, Ryan, Snow, Adam, Nayak, Kamakshi, Shanbhogue, Prajna, Meyer, Austin G., Redpath, Gregory M.I., Hinderliter, Anne, Cooper, Sandra T., Sutton, R. Bryan
• Format: Article
• Language: English
• Subjects: Alternative Splicing; Amino Acid Sequence; Animals; Calcium - metabolism; Cell Line; Crystallography, X-Ray; Dysferlin; Humans; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Models, Molecular; Molecular Sequence Data; Muscle Proteins - chemistry; Muscle Proteins - genetics; Muscle Proteins - metabolism; Mutagenesis, Site-Directed; Myoblasts - cytology; Myoblasts - metabolism; Protein Binding; Protein Structure, Tertiary; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Regeneration; RNA, Messenger - genetics; RNA, Messenger - metabolism; Sarcolemma - metabolism; Sarcolemma - ultrastructure; Thermodynamics
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2013.10.001

Dysferlin plays a critical role in the Ca2+-dependent repair of microlesions that occur in the muscle sarcolemma. Of the seven C2 domains in dysferlin, only C2A is reported to bind both Ca2+ and phospholipid, thus acting as a key sensor in membrane repair. Dysferlin C2A exists as two isoforms, the “canonical” C2A and C2A variant 1 (C2Av1). Interestingly, these isoforms have markedly different responses to Ca2+ and phospholipid. Structural and thermodynamic analyses are consistent with the canonical C2A domain as a Ca2+-dependent, phospholipid-binding domain, whereas C2Av1 would likely be Ca2+-independent under physiological conditions. Additionally, both isoforms display remarkably low free energies of stability, indicative of a highly flexible structure. The inverted ligand preference and flexibility for both C2A isoforms suggest the capability for both constitutive and Ca2+-regulated effector interactions, an activity that would be essential in its role as a mediator of membrane repair. •Human dysferlin C2A domains are weakly stable•Alternate splicing of dysferlin is a key aspect to membrane repair•The C2A domains of dysferlin possess opposite ligand binding properties•The C2A domains of dysferlin possess a nanomolar affinity Ca2+ binding site Dysferlin is a membrane protein with a critical role in resealing tears in muscle cell membranes. Fuson et al. solve structures of the two isoforms of the first C2 domain in human dysferlin and examine their stability. The two isoforms exist on the edge of protein stability, likely linked to the fusogen activity.