Ca+2-dependent secretion activator 1 (Ca+2-dependent activator protein for secretion 1, CAPS-1, CADPS, CAPS, CAPS1, KIAA1121)
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Function
- Ca+2-binding protein
- role in exocytosis of vesicles containing neurotransmitters & neuropeptides
- probably acts upstream of fusion in the biogenesis or maintenance of mature secretory vesicles
- preferentially binds to dense-core vesicles (DCV) but not to small clear synaptic vesicles
- binds phosphoinosides, with a strong selectivity for PIP2 over PIP3
- may specifically mediate the Ca+2-dependent exocytosis of large dense-core vesicles as PIP2-binding protein
- acts at prefusion step following ATP-dependent priming
- role in dense-core vesicle membrane fusion
- role in small clear synaptic vesicles exocytosis
- unclear whether function related to Ca+2 triggering
- regulates catecholamine loading of dense-core vesicles
- interacts with the dopamine receptor DRD2
Structure
- homodimer
- contains 1 C2 domain
- contains 1 MHD1 domain (MUNC13 homology domain 1)
- contains 1 PH domain
- essential for regulated exocytosis binds phospholipids & plasma membrane
Compartment
- cytoplasmic vesicle, membrane-associated
- strongly enriched in synaptic fractions
- probably localizes to different vesicles than CADPS2
Alternative splicing
named isoforms=5
Expression
- specifically expressed in neural & endocrine secretory tissues
- expressed in brain & pancreas > heart
- expressed in fetal heart, cerebellum, cerebral cortex, medulla oblongata, occipital pole, frontal & temporal lobes, putamen
- weak expression in spinal cord