Synaptophysin is an ~38kD integral membrane protein involved in neurotransmitter exocytosis present on synaptic vesicles. This protein consists of four transmembrane domains, with its amino- and carboxyl-terminus facing the cytoplasm. Due to its transmembrane domain structure, synaptophysin has been postulated to be a gap junction-like protein because voltage-dependent channel activity is seen when synaptophysin hexamers are reconstituted into lipid membranes. Recent studies have shown synaptophysin to be a major cholesterol-binding protein in brain synaptic vesicles and it has been proposed that this cholesterol-binding ability may be of key importance in the generation of synaptic vesicles at plasma membranes. A regional reduction of synaptophysin was found in patients with Alzheimer’s disease and schizophrenia.
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