Calpain cleavage within dysferlin exon 40a releases a synaptotagmin-like module for membrane repair.
Bottom Line: Here we show that injury-activated cleavage of dysferlin is mediated by the ubiquitous calpains via a cleavage motif encoded by alternately spliced exon 40a.Of importance, we reveal that myoferlin and otoferlin are also cleaved enzymatically to release similar C-terminal modules, bearing two C2 domains and a transmembrane domain.Evolutionary preservation of this feature highlights its functional importance and suggests that this highly conserved C-terminal region of ferlins represents a functionally specialized vesicle fusion module.
Affiliation: Institute for Neuroscience and Muscle Research, Children's Hospital at Westmead, Sydney, NSW 2145, Australia Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia.Show MeSH
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Mentions: To determine whether there is one dominant exon 40a-containing dysferlin transcript, we derived primer sets flanking each of the alternately spliced exons 5a, 17, and 40a and analyzed their relative abundance among dysferlin transcripts derived from a panel of human tissues (Clontech Multiple Tissue cDNA panels I and II; Figure 3A). Exon 40a-containing dysferlin transcripts are abundantly expressed in most human tissues (40–60% of transcripts in liver, kidney, lung, placenta, and pancreas; Figure 3A). Skeletal muscle expresses the lowest relative levels of exon 40a–containing transcripts (∼10–15%), with heart and brain expressing intermediate levels (∼15–25%). Exon 5a–containing transcripts dominate in liver, kidney, lung, placenta, and pancreas (80–90% of transcripts). Exon 17 shows variable tissue-specific expression, comprising the dominant mRNA species in liver, heart, brain, and muscle but only a minor mRNA species in kidney, lung, placenta, and pancreas. Our results therefore suggest that in human tissues exon 40a is regularly copresent with exon 5a and sometimes copresent with exon 17; this is consistent with previous results by Pramono et al. (2009), who compared splice isoforms of dysferlin in skeletal muscle and peripheral blood monocytes.
Affiliation: Institute for Neuroscience and Muscle Research, Children's Hospital at Westmead, Sydney, NSW 2145, Australia Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia.