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

Abstract

SUMMARY 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.

Disease-modifying effects of orally bioavailable NF-κB inhibitors in dystrophin-deficient muscle

“…While total Dysf gene expression was nearly 2-fold higher in treated mice ( Figure 7E), expression of the canonical (calcium sensitive) C2A isoform of Dysf was significantly reduced. Instead, we found a nearly 14-fold increase in the expression of the C2A variant 1 (C2Av1), which is largely calcium insensitive and has a high affinity for phospholipids (27). A 40% increase in expression of Dysf containing exon 40a, which expresses the calpain-susceptible cleavage site to release the C72 fragment (25), was also found.…”

Auditory neuropathy — neural and synaptic mechanisms

“…The sequence similarity between ferlin C 2 domains and other C 2 domain proteins, such as protein kinase C or synaptotagmin, is low, making it difficult to infer the structural determinants of oto ferlin binding to Ca 2+ and phospholipid from those of better characterized proteins 25 . We are only beginning to obtain insight into the protein structure of ferlins 55,56 . To date, approximately 90 pathogenic mutations of OTOF have been reported; the majority of these muta tions are assumed to be nonsense or truncation mutations that cause inactivation of otoferlin 57 , result ing in DFNB9type hearing impairment.…”

Cellular and molecular interactions of phosphoinositides and peripheral proteins

“…Alternative splicing of some C2 domains may also regulate their lipid and/or Ca 2+ -binding properties. The C2A domain of Dysferlin has been shown to have a canonical C2A and a variant (C2Av1) these two molecules have different Ca 2+ -binding properties and different ligand preferences (Fuson et al 2013). In addition to diverse roles in Ca 2+ selectivity and lipid-binding some C2 domains have been shown to induce membrane curvature changes upon membrane association (Martens et al 2007; Hui et al 2009; Ward et al 2012; Yu et al 2013; Sot et al 2013).…”