Synaptophysin, also known as the major synaptic vesicle protein p38, is a protein that in humans is encoded by the SYP gene. [5] [6]
Synaptophysin, also known as the major synaptic vesicle protein p38, is a protein that in humans is encoded by the SYP gene. [5] [6]
The gene is located on the short arm of X chromosome (Xp11.23-p11.22). It is 12,406 bases in length and lies on the minus strand. The encoded protein has 313 amino acids with a predicted molecular weight of 33.845 kDa.
The protein is a synaptic vesicle glycoprotein with four transmembrane domains weighing 38 kDa. It is present in neuroendocrine cells and in virtually all neurons in the brain and spinal cord that participate in synaptic transmission. It acts as a marker for neuroendocrine tumors, and its ubiquity at the synapse has led to the use of synaptophysin immunostaining for quantification of synapses. [7]
The exact function of the protein is unknown: it interacts with the essential synaptic vesicle protein synaptobrevin, but when the synaptophysin gene is experimentally inactivated in animals, they still develop and function normally. [8] Recent research has shown, however, that elimination of synaptophysin in mice creates behavioral changes such as increased exploratory behavior, impaired object novelty recognition, and reduced spatial learning. [9]
This gene has been implicated in X-linked intellectual disability. [10]
Using immunohistochemistry, synaptophysin can be demonstrated in a range of neural and neuroendocrine tissues, [11] including cells of the adrenal medulla and pancreatic islets. As a specific marker for these tissues, it can be used to identify tumours arising from them, such as neuroblastoma, retinoblastoma, phaeochromocytoma, carcinoid, small-cell carcinoma, medulloblastoma and medullary thyroid carcinoma, among others. Diagnostically, it is often used in combination with chromogranin A. [12]
Synaptophysin has been shown to interact with AP1G1 [13] and SIAH2. [14]
The synapsins are a family of proteins that have long been implicated in the regulation of neurotransmitter release at synapses. Specifically, they are thought to be involved in regulating the number of synaptic vesicles available for release via exocytosis at any one time. Synapsins are present in invertebrates and vertebrates and are strongly conserved across all species. They are expressed in highest concentration in the nervous system, although they also express in other body systems such as the reproductive organs, including both eggs and spermatozoa. Synapsin function also increases as the organism matures, reaching its peak at sexual maturity.
Synaptosomal-Associated Protein, 25kDa (SNAP-25) is a Target Soluble NSF (N-ethylmaleimide-sensitive factor) Attachment Protein Receptor (t-SNARE) protein encoded by the SNAP25 gene found on chromosome 20p12.2 in humans. SNAP-25 is a component of the trans-SNARE complex, which accounts for membrane fusion specificity and directly executes fusion by forming a tight complex that brings the synaptic vesicle and plasma membranes together.
Syntaxin-1A is a protein that in humans is encoded by the STX1A gene.
Ras-related protein Rab-3A is a protein that in humans is encoded by the RAB3A gene. It is involved in calcium-triggered exocytosis in neurons.
Disks large homolog 3 (DLG3) also known as neuroendocrine-DLG or synapse-associated protein 102 (SAP-102) is a protein that in humans is encoded by the DLG3 gene. DLG3 is a member of the membrane-associated guanylate kinase (MAGUK) superfamily of proteins.
Synaptotagmin-1 is a protein that in humans is encoded by the SYT1 gene.
Vesicle-associated membrane protein 2 (VAMP2) is a protein that in humans is encoded by the VAMP2 gene.
Amyloid beta A4 precursor protein-binding family A member 1 is a protein that in humans is encoded by the APBA1 gene.
Neurexin-1-alpha is a protein that in humans is encoded by the NRXN1 gene.
Complexin-2 is a protein that in humans is encoded by the CPLX2 gene.
Regulating synaptic membrane exocytosis protein 1 is a protein that in humans is encoded by the RIMS1 gene.
Rabphilin-3A is a protein that in humans is encoded by the RPH3A gene. It contains two C2 domains and binds calcium ions at low micromolar concentration. Rabphilin was shown to regulate neurotransmitter release in hippocampal neurons after neurons had an increased synaptic activity and their release rate was depressed.
Protein unc-13 homolog B is a protein that in humans is encoded by the UNC13B gene.
DnaJ homolog subfamily C member 5, also known as cysteine string protein or CSP is a protein, that in humans encoded by the DNAJC5 gene. It was first described in 1990.
Synaptophysin-like protein 1 is a protein that in humans is encoded by the SYPL1 gene.
Synaptoporin is a protein that in humans is encoded by the SYNPR gene.
Synaptogyrin-1 is a protein that in humans is encoded by the SYNGR1 gene.
Double C2-like domain-containing protein beta is a protein that in humans is encoded by the DOC2B gene.
Synapsin I, is the collective name for Synapsin Ia and Synapsin Ib, two nearly identical phosphoproteins that in humans are encoded by the SYN1 gene. In its phosphorylated form, Synapsin I may also be referred to as phosphosynaspin I. Synapsin I is the first of the proteins in the synapsin family of phosphoproteins in the synaptic vesicles present in the central and peripheral nervous systems. Synapsin Ia and Ib are close in length and almost the same in make up, however, Synapsin Ib stops short of the last segment of the C-terminal in the amino acid sequence found in Synapsin Ia.
Synapsin II is the collective name for synapsin IIa and synapsin IIb, two nearly identical phosphoproteins in the synapsin family that in humans are encoded by the SYN2 gene. Synapsins associate as endogenous substrates to the surface of synaptic vesicles and act as key modulators in neurotransmitter release across the presynaptic membrane of axonal neurons in the nervous system.