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Cell Rep. 2014 Nov 6;9(3):902-9. doi: 10.1016/j.celrep.2014.09.050. Epub 2014 Oct 23.

Secretory vesicle priming by CAPS is independent of its SNARE-binding MUN domain.

Author information

1
Institute of Physiology, Saarland University, Building 59, 66421 Homburg/Saar, Germany.
2
Neurophysiology Group, Max-Planck-Institute of Experimental Medicine, 37075 Göttingen, Germany; Department of Molecular Neurobiology, Max-Planck-Institute of Experimental Medicine, 37075 Göttingen, Germany.
3
Department of Molecular Neurobiology, Max-Planck-Institute of Experimental Medicine, 37075 Göttingen, Germany.
4
Institute of Physiology, Saarland University, Building 59, 66421 Homburg/Saar, Germany. Electronic address: jrettig@uks.eu.

Abstract

Priming of secretory vesicles is a prerequisite for their Ca(2+)-dependent fusion with the plasma membrane. The key vesicle priming proteins, Munc13s and CAPSs, are thought to mediate vesicle priming by regulating the conformation of the t-SNARE syntaxin, thereby facilitating SNARE complex assembly. Munc13s execute their priming function through their MUN domain. Given that the MUN domain of Ca(2+)-dependent activator protein for secretion (CAPS) also binds syntaxin, it was assumed that CAPSs prime vesicles through the same mechanism as Munc13s. We studied naturally occurring splice variants of CAPS2 in CAPS1/CAPS2-deficient cells and found that CAPS2 primes vesicles independently of its MUN domain. Instead, the pleckstrin homology domain of CAPS2 seemingly is essential for its priming function. Our findings indicate a priming mode for secretory vesicles. This process apparently requires membrane phospholipids, does not involve the binding or direct conformational regulation of syntaxin by MUN domains of CAPSs, and is therefore not redundant with Munc13 action.

PMID:
25437547
DOI:
10.1016/j.celrep.2014.09.050
[Indexed for MEDLINE]
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