The Journal of Neuroscience, August 15, 2000, 20(16):5997-6006
A Novel SNAP25-Caveolin Complex Correlates with the Onset of
Persistent Synaptic Potentiation
Janice E. A.
Braun1 and
Daniel V.
Madison2
1 Department of Physiology and Biophysics, Neuroscience
Research Group, The University of Calgary, Calgary, Alberta, Canada T2N
4N1, and 2 Department of Molecular and Cellular Physiology,
Stanford University Medical Center, Stanford, California 94305-5428
We have identified synaptic protein complexes in intact rat
hippocampal slices using the rapid chemical cross-linking reagent paraformaldehyde. Cellular proteins were rapidly cross-linked, solubilized, separated electrophoretically by SDS-PAGE, and then identified immunologically. Multiple complexes containing syntaxin, the
synaptosomal-associated protein of 25 kDa (SNAP25), and
vesicle-associated membrane protein (VAMP) were observed to coexist in
a single hippocampal slice including a 100 kDa cross-linked protein
complex that exhibited the same electrophoretic migration as a member
of the previously identified SDS-resistant soluble
N-ethylmaleimide-sensitive fusion attachment protein
receptor "core" of the 20 S complex. A VAMP-synaptophysin complex, reported previously in vitro, was also observed
in the hippocampal slices. This study links biochemical and
physiological studies involving presynaptic proteins implicated in
secretion and confirms that these proteins that have been studied
extensively previously in the presence of detergent do form "bona
fide" cellular complexes. Importantly, we have also detected
additional novel protein complexes that do not correspond to complexes
identified previously in vitro. After the induction of
persistent synaptic potentiation, an abundant 40 kDa SNAP25-caveolin1
complex was observed. The SNAP25-caveolin1 complex was not abundant in
control slices and, therefore, represents the first demonstration of a reorganization of protein complexes in intact hippocampal slices during
the induction of synaptic potentiation. The interaction between
caveolin1 and SNAP25 was confirmed biochemically by demonstration of
the association of caveolin with recombinant-immobilized SNAP25 and by
the coimmunoprecipitation of SNAP25 using caveolin-specific antisera.
Caveolin1, like SNAP25, was observed to be abundant in isolated
hippocampal nerve terminals (synaptosomes). Immunofluorescent studies
demonstrated that both SNAP25 and caveolin1 are present in neurons and
colocalize in axonal varicosities. These results suggest that a
short-lasting SNAP25-caveolin interaction may be involved in the early
phase of synaptic potentiation.
Key words:
synaptic protein; caveolin; SNAP25; hippocampus; synaptic
potentiation; paraformaldehyde
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