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Calcium‐Dependent Self‐Association of Synaptotagmin I
Author(s) -
Damer Cynthia K.,
Creutz Carl E.
Publication year - 1996
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1996.67041661.x
Subject(s) - synaptotagmin 1 , vesicle , calcium , c2 domain , cytoplasm , biochemistry , microbiology and biotechnology , biophysics , chemistry , stx1a , biology , membrane , synaptic vesicle , organic chemistry
Synaptotagmin I, an integral membrane protein of secretory vesicles, appears to have an essential role in calcium‐triggered hormone and neurotransmitter release. The large cytoplasmic domain of synaptotagmin I has two C2 domains that are thought to mediate calcium and phospholipid binding. A recombinant protein (p65 1–5) comprised of the cytoplasmic domain was previously shown to aggregate purified chromaffin granules and artificial phospholipid vesicles in a calcium‐dependent manner. p65 1–5 may be able to aggregate membrane vesicles by a self‐association reaction. This hypothesis led us to investigate the ability of synaptotagmin I protein fragments to multimerize in vitro. We found that p65 1–5, in the absence of membranes, was able to self‐associate to form large aggregates in a calcium‐dependent manner as shown by light‐scattering assays and electron microscopy. In addition, a recombinant protein comprised of only the second half of the cytoplasmic domain, including the second C2 domain, was also able to self‐associate and aggregate phospholipid vesicles in a calcium‐dependent manner. A recombinant protein comprised of only the first C2 domain was not able to self‐associate or aggregate vesicles. These results suggest that synaptotagmin I is able to bind calcium in the absence of membranes and that the second half of the cytoplasmic domain is able to bind calcium and mediate its multimerization in a calcium‐dependent manner. The ability of synaptotagmin I protein fragments to multimerize in a calcium‐dependent manner in vitro suggests that multimerization may have an important function in vivo.