Synaptophysin (SYP)

Synaptophysin is an abundant 38 kDa integral membrane glycoprotein of small synaptic vesicles, encoded by the SYP gene located on chromosome Xp11.23-p11.22 in humans[2][5]. It is characterized by four transmembrane domains and belongs to the MARVEL domain family of proteins involved in membrane trafficking and apposition[1][6]. Synaptophysin is highly expressed in neurons and neuroendocrine cells and serves as a marker for these cell types in diagnostic pathology[2]. Its precise physiological function remains uncertain, but it is known to interact with synaptobrevin and participate in synaptic vesicle trafficking, exocytosis, and possibly in regulating vesicle fusion through its associations with SNARE proteins and V-ATPase complexes[1][3][4]. It binds cholesterol and cytoplasmic calcium, although the exact consequences of these interactions are not fully elucidated[3]. Synaptophysin is widely used as a biomarker for neuroendocrine tumors (e.g., neuroblastoma, small-cell carcinoma) and for quantifying synapses in neuroscience research due to its ubiquitous presence at neuronal synapses[2]. Mutations in SYP have been implicated in X-linked intellectual disability[2]. Despite its abundance, mice lacking synaptophysin demonstrate only subtle behavioral abnormalities, and no drugs currently target it directly as a therapeutic mechanism, so it is not considered a therapeutic target as of current knowledge[2][3].

Other names

major synaptic vesicle protein p38p38