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UL16 Binding Protein 3 (ULBP3) is a ligand for the NKG2D receptor in NK cells. ULBPs activate different signaling pathways resulting in the production of cytokines and chemokines. ULBP3 is a ligand for the KLRK1/NKG2D receptor, along with at least ULBP1 and ULBP2. Binding of ULBPs ligands to KLRK1/NKG2D stimulates calcium mobilization and activation of the JAK2, STAT5, ERK and PI3K kinase/Akt signal transduction pathway. ULBP3 has lower affinity for KLRK1/NKG2D compared to ULBP1 and ULBP2 and stimulates weaker signaling responses than does ULBP2 or ULBP1.

UL16 Binding Protein 4 (ULBP4) is a member of the RAET1 family, which is comprised of major histocompatibility complex (MHC) class I-related genes located in a cluster on chromosome 6q24.2-q25.3. ULBP4 functions as a ligand for the NKG2D receptor on the surface of NK cells. ULBP4 binding to the receptor induces expansion of anti-tumor cytotoxic lymphocytes. ULBP4 is expressed mainly in the skin, but also in the testis or trachea. ULBP4 is upregulated in different tumors. ULBP4 doesn’t interact with the CMV glycoprotein UL16. ULBP4 is also a ligand for the KLRK1 receptor. ULBP4 distributes activating signals to NK cells and stimulates tumor immune surveillance by inducing the expansion of anti-tumor cytotoxic lymphocytes.

Uromodulin is the most abundant protein in normal urine. Its secretion in urine follows proteolytic cleavage of the ectodomain of its glycosyl phosphatidylinosital-anchored counterpart that is situated on the luminal cell surface of the loop of Henle. Uromodulin plays a role as a constitutive inhibitor of calcium crystallization in renal fluids. Secretion of uromodulin in urine provides protection against urinary tract infections caused by uropathogenic bacteria. Defects in Uromodulin expression are associated with the autosomal dominant renal disorders medullary cystic kidney disease-2 (MCKD2) and familial juvenile hyperuricemic nephropathy (FJHN). These disorders are characterized by juvenile onset of hyperuricemia, gout, and progressive renal failure. While several transcript variants may exist for this gene, the full-length natures of only two have been described to date. UMOD is involved in regulating the circulating activity of cytokines as it binds to il-1, il-2 and tnf with high affinity.

Uromodulin is the most abundant protein in normal urine. Its secretion in urine follows proteolytic cleavage of the ectodomain of its glycosyl phosphatidylinosital-anchored counterpart that is situated on the luminal cell surface of the loop of Henle. Uromodulin plays a role as a constitutive inhibitor of calcium crystallization in renal fluids. Secretion of uromodulin in urine provides protection against urinary tract infections caused by uropathogenic bacteria. Defects in Uromodulin expression are associated with the autosomal dominant renal disorders medullary cystic kidney disease-2 (MCKD2) and familial juvenile hyperuricemic nephropathy (FJHN). These disorders are characterized by juvenile onset of hyperuricemia, gout, and progressive renal failure. While several transcript variants may exist for this gene, the full-length natures of only two have been described to date. UMOD is involved in regulating the circulating activity of cytokines as it binds to il-1, il-2 and tnf with high affinity.

Uromodulin is the most abundant protein in normal urine. Its secretion in urine follows proteolytic cleavage of the ectodomain of its glycosyl phosphatidylinosital-anchored counterpart that is situated on the luminal cell surface of the loop of Henle. Uromodulin plays a role as a constitutive inhibitor of calcium crystallization in renal fluids. Secretion of uromodulin in urine provides protection against urinary tract infections caused by uropathogenic bacteria. Defects in Uromodulin expression are associated with the autosomal dominant renal disorders medullary cystic kidney disease-2 (MCKD2) and familial juvenile hyperuricemic nephropathy (FJHN). These disorders are characterized by juvenile onset of hyperuricemia, gout, and progressive renal failure. While several transcript variants may exist for this gene, the full-length natures of only two have been described to date. UMOD is involved in regulating the circulating activity of cytokines as it binds to il-1, il-2 and tnf with high affinity.

Uromodulin is the most abundant protein in normal urine. Its secretion in urine follows proteolytic cleavage of the ectodomain of its glycosyl phosphatidylinosital-anchored counterpart that is situated on the luminal cell surface of the loop of Henle. Uromodulin plays a role as a constitutive inhibitor of calcium crystallization in renal fluids. Secretion of uromodulin in urine provides protection against urinary tract infections caused by uropathogenic bacteria. Defects in Uromodulin expression are associated with the autosomal dominant renal disorders medullary cystic kidney disease-2 (MCKD2) and familial juvenile hyperuricemic nephropathy (FJHN). These disorders are characterized by juvenile onset of hyperuricemia, gout, and progressive renal failure. While several transcript variants may exist for this gene, the full-length natures of only two have been described to date. UMOD is involved in regulating the circulating activity of cytokines as it binds to il-1, il-2 and tnf with high affinity.

Uridine 5'-monophosphate synthase (UMPS), is a bifunctional enzyme that catalyzes the ultimate two steps of the de novo pyrimidine biosynthetic pathway. UMPS in eukaryotes links the orotate phosphoribosyltransferase and the orotidine-5’-monophosphate (OMP) decarboxylase activities into a single protein. The harmony of these 2 enzymes is assumed to be stabilized the catalytic centers as a result of the low molar concentration of the protein in mammalian cells.mutations in this gene are the reason of inherited orotic aciduria disease.

Uridine 5'-monophosphate synthase (UMPS), is a bifunctional enzyme that catalyzes the ultimate two steps of the de novo pyrimidine biosynthetic pathway. UMPS in eukaryotes links the orotate phosphoribosyltransferase and the orotidine-5’-monophosphate (OMP) decarboxylase activities into a single protein. The harmony of these 2 enzymes is assumed to be stabilized the catalytic centers as a result of the low molar concentration of the protein in mammalian cells. Mutations in UMPS are the reason of inherited orotic aciduria disease.

UCN119B is a member of the PDE6D/unc-119 family. UCN119B has a large number of photoreceptors of the retina. Additionaly, UCN119B has a strong homology with the C. elegans unc119 and is able to functionally complement the C. elegans unc119 mutation gene.

UNC-5 Netrin Receptor B or UNC5B, is part of the UNC5 family that has 4 linked receptors and act as a axon guidance molecule Netrin-1 receptor. UNC5B promotes inhibitionleukocyte migration, capillary branching and osteoclast differentiation that are Netrin-1-mediated. UNC5B is responsible for the activation of DAPK1 that can cause apoptosis. The protein takes part in tumorgenesis, development of atherosclerosis and tubular epithelial cells survival when an acute injury in the kidney occurs.

E.Coli Uracil DNA Glycosilase (UNG) catalyses the release of free Uracil from Uracil-containing DNA. UNG efficiently hydrolyzes uracil from signle-stranded or double-stranded DNA, but not from oligomers (6 fewer bases).

UNG is a member of the Uracil-DNA glycosylase family. One of his functions is to prevent mutagenesis by eliminating uracil from DNAmolecules by cleaving the N-glycosylic bond and initiating the base-excision repair (BER) pathway. Uracil basesare formed as a result of cytosine deamination or misincorporation of dUMP residues. After a mutation is formed, the mutagenicthreat of uracil propagates through any subsequent DNA replication steps. Among the diseases associated with UNG are: congenital rubella, and immunodeficiency with hyper igm type 4.

Uracil DNA glycosylase (UDG), or uracil-DNA glycosylase 1, is a crucial enzyme found in all life forms, involved in repairing damaged DNA by specifically removing uracil bases that are misincorporated into DNA during replication or deaminated cytosine. In various organisms, UDG goes by different names, such as b2580, JW2564, EC 3.2.2.27, DGU, UNG15, HIGM5, EC 3.2.2, HIGM4, and UNG2. Here, we delve into the E. coli UDG, examining its structure, function, and applications in molecular biology.

Structure: The crystal structure of E. coli UDG has been extensively studied, revealing that it belongs to the uracil DNA glycosylase (UDG) superfamily. The E. coli UDG monomer has 229 amino acids with a molecular weight of 25 kDa. The protein has a beta-sheet-rich structure with an alpha-helix on one side and a groove on the other side that binds to DNA. The active site of E. coli UDG contains a conserved glutamic acid residue that acts as a catalytic base to facilitate the hydrolysis of the N-glycosidic bond between uracil and the sugar phosphate backbone.

Function: E. coli UDG plays a critical role in maintaining the integrity of the genome by preventing the accumulation of mutations that can arise from the incorporation of uracil into DNA. Uracil in DNA can occur spontaneously from the deamination of cytosine or can be incorporated during DNA synthesis when dUTP is used instead of dTTP. Unrepaired uracil bases can lead to DNA damage and genomic instability, possibly resulting in cell death or disease. E. coli UDG specifically recognizes and removes uracil bases from DNA, creating an abasic site that is further processed by other repair enzymes.

E. coli UDG is a valuable tool in molecular biology research for its ability to remove uracil from DNA templates. This enzyme is widely used in various applications, including site-directed mutagenesis, PCR amplification, and sequencing. UDG can remove uracil from the template strand of a DNA duplex, enabling the introduction of specific mutations or the creation of nicked DNA for downstream applications. Additionally, UDG is used in PCR amplification to prevent the amplification of any residual uracil-containing templates, which can lead to false-positive results. UDG has also been used in sequencing applications to remove uracil from DNA templates before sequencing, improving the accuracy and reliability of the results.

Conclusion: E. coli UDG is a highly conserved enzyme that plays a crucial role in maintaining genomic integrity by removing uracil from DNA. The crystal structure of E. coli UDG has been extensively studied, revealing the conserved catalytic mechanism and the interaction of the protein with DNA. E. coli UDG is a valuable enzyme with numerous applications in molecular biology research and potential applications in the medical field, such as cancer treatment. More research is needed to fully understand the therapeutic potential of targeting UDG. Overall, E. coli UDG is a valuable enzyme with numerous applications in molecular biology research and potential applications in the medical field.

Uroplakin 2 (UPK2) is one of the proteins of the highly urothelium-specific integral membrane proteins of the asymmetric unit membrane which forms urothelium apical plaques in mammals. The asymmetric unit membrane is thought to strengthen the urothelium by preventing cell rupture during bladder distention. The UPK2 protein is expressed in the peripheral blood of bladder cancer patients with transitional cell carcinomas.

UPK3A is a member of the uroplakin-3 family. Uroplakins (UP) which are transmembrane proteins are important components of the urothelium that pass the lipid bilayer once (UPII, UPIIIa, and UPIIIb) or four times (UPIa and UPIb; both members of the "tetraspanin" family). All hold great luminal/extracellular domains, but only UPIIIa and UPIIIb have significant cytoplasmic shares in their C-termini. UPK3A is an extremely specific and moderately sensitive immunohistochemical marker for primary and metastatic urothelial carcinomas. Alterations in this gene are related to renal adysplasia.

UPP1 catalyzes the reversible phosphorylytic cleavage of uridine and deoxyuridine to uracil and ribose- or deoxyribose-1-phosphate which are used as carbon and energy sources or in the release of pyrimidine bases for nucleotide synthesis. UPP1 is part of the family of glycosyltransferases, specifically the pentosyltransferases. Pyrimidine nucleoside phosphorylases add ribose or deoxyribose to pyrimidine bases to form nucleosides that can be incorporated into RNA or DNA.

UPP1 catalyzes the reversible phosphorylytic cleavage of uridine and deoxyuridine to uracil and ribose- or deoxyribose-1-phosphate which are used as carbon and energy sources or in the release of pyrimidine bases for nucleotide synthesis. UPP1 is part of the family of glycosyltransferases, specifically the pentosyltransferases. Pyrimidine nucleoside phosphorylases add ribose or deoxyribose to pyrimidine bases to form nucleosides that can be incorporated into RNA or DNA.

Uridine phosphorylase from Salmonella typhimurium (StUP) catalyzes the reversible phosphorolysis of uridine with the formation of ribose-1-phosphate and uracil.

UPRT is a uracil phosphoribosyltransferase, that catalyzes the alteration of uracil and 5-phosphoribosyl-1-R-diphosphate to uridine monophosphate (UMP). This reaction is a significant part of nucleotide metabolism, specifically the pyrimidine salvage pathway. UPRT is restricted to the nucleus and cytoplasm and is a possible target for rational design of drugs to cure cancer and parasitic infections.

Ubiquinol-Cytochrome C Reductase Core Protein I (UQCRC1) is a member of the peptidase M16 family,UQCRC1/QCR1 subfamily. UQCRC1 is a part of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome b-c1 complex), which is component of the mitochondrial respiratory chain. UQCRC1 can mediate formation of the complex between cytochromes c and c1.

Cytochrome b-c1 complex subunit 2, mitochondrial (UQCRC2) is a member of the peptidase M16 family. UQCRC2 is a component of the ubiquinol-cytochrome c reductase complex (complex III), which is a part of the mitochondrial respiratory chain. UQCRC2 is essential for the compilation of the complex.

Ubiquinol-Cytochrome C Reductase Hinge Protein (UQCRH) is a member of the UQCRH/QCR6 family. UQCRH is a component of the ubiquinol-cytochrome c reductase complex (complex III or cytochrome b-c1 complex), which is part of the mitochondrial respiratory chain. The UQCRH protein mediates formation of the complex between cytochromes c and c1.

Ubiquinol-Cytochrome C Reductase (UQCRQ) is a small core-associated protein and a subunit of ubiquinol-cytochrome c reductase complex III that belongs to the mitochondrial respiratory chain. UQCRQ is also a ubiquinone-binding protein of low molecular mass.

Urate oxidase catalyzes the enzymatic oxidation (degrades) of uric acid into allantoin, an inactive and soluble metabolite, which is 5 to 10 fold more soluble than uric acid . Urate oxidase is an enzyme of the purine breakdown pathway that catalyses the oxidation of uric acid to allantoin. Uricase is present in numerous diverse organisms, but not in higher primates including human. Hyperuricaemia is most commonly associated with gout and also occurs in mammalians with malignancy, especially those with lymphoid malignancies due to rapid cell turnover and an increased rate of purine metabolism. Uricase is effective in the prevention and treatment of hyperuricaemia in mammalians with malignancy and in those who have undergone transplantation. It appears to act rapidly, safely and induces a more dramatic decrease in plasma levels of uric acid.

URM1 is ubiquitin-related modifier 1 homolog protein which mainly functions in the post-translational modification of proteins via the urmylation pathway. Urm1 covalently binds to its E1 activating enzyme, Uba4p, to conjugate alkyl hydroperoxide reductase (Ahp1) as determined by studies with Saccharomyces cerevisiae. It has been theorized that this complex may then have a role in the oxidative-stress response in mammals.

UROD is the fifth enzyme in the human heme biosynthetic pathway and is in charge for the transfer of uroporphyrinogen to coproporphyrinogen through the deletion of four carboxymethyl side chains. UROD Mutations and deficiency result in 3 autosomal disorders in humans: familial porphyria cutanea tarda (f-PCT), sporadic porphyria cutanea tarda (s-PCT) and hepatoerythropoietic porphyria (HEP).

Urokinase (UK) is a serine protease, which is one of biological plasminogen activators.
It is involved in a number of biological functions including fibrinolysis, embryogenesis, cell migration, tissue remodeling, ovulation, and wound healing.
It can be obtained from human urine or kidney cell culture.

Urokinase (UK) is a serine protease, which is one of biological plasminogen activators.
It is involved in a number of biological functions including fibrinolysis, embryogenesis, cell migration, tissue remodeling, ovulation, and wound healing.
It can be obtained from human urine or kidney cell culture.

Uroporphyrinogen III synthase (UROS) is an enzyme involved in the 4th step of porphyrin metabolism and in the conversion of hydroxymethyl bilane into uroporphyrinogen III. Defects in the UROS protein can cause molecular lesions which lead to the autosomal recessive Gunther disease, otherwise known as congenital erythropoietic porphyria (CEP).

USE1 Belongs to the USE1 family, this protein is a vesicle transport protein. USE1 is a component of a SNAREcomplex consisting of STX18, USE1L, BNIP1/SEC20L and SEC22B. In addition USE1 interacts directly with STX18. SNARE maybe involved in targeting and fusion of Golgi-derived retrograde transport vesicles with the ER. Diseases associated with USE1 comprise dysentery and hemolytic-uremic syndrome. Among its related super-pathways are Nicotine Pathway (Dopaminergic Neuron) and Pharmacodynamics. GO annotations related to this gene include protein binding.

Upstream Transcription Factor 1 (USF1) belongs to the basic helix-loop-helix leucine zipper family, and functions as a cellular transcription factor. USF1 activates transcription via pyrimidine-rich initiator (Inr) elements and E-box motifs. The USF1 gene has been linked to familial combined hyperlipidemia (FCHL). USF1 is a transcription factor which binds to a symmetrical DNA sequence (E-boxes) (5'-CACGTG-3') found in a various viral and cellular promoters.

USH1C gene product Harmonin, is a scaffold protein which functions in the assembly of Usher protein complexes. Harmonin is able to attach to various proteins in cell membranes and coordinate their activities. Harmonin contains PDZ domains, a coiled-coil region with a bipartite nuclear localization signal and a PEST degradation sequence. USH1C is expressed in the small intestine, colon, kidney, eye, vestibule of the inner ear and weakly in the pancreas.
Mutations in the USH1C gene cause the Usher syndrome type I which is an autosomal recessive sensory defect involving congenital profound sensorineural deafness, vestibular dysfunction, and blindness due to progressive retinitis pigmentosa. Sensorineural deafness is caused by damage to the neural receptors of the inner ear, the nerve pathways to the brain, or the area of the brain that receives sound information. The 3 types of the Usher syndrome (1- 3) are distinguished by age at onset and differences in auditory and vestibular function. USH1C gene defects cause of non-syndromic sensorineural deafness autosomal recessive type 18 (DFNB18), is a form of sensorineural hearing loss.

USP14 belongs to the ubiquitin-specific processing (UBP) family of proteases which is a deubiquitinating enzyme (DUB) containing His and Cys domains. USP14 placed in the cytoplasm and cuts the ubiquitin from ubiquitin-fused precursors and ubiquitinylated proteins.a mutation which results in reduced expression of the ortholog of USP14 in mice inhibits growth, develop severe tremors by 2 to 3 weeks of age followed by paralysis and death by 6 to 10 weeks of age.

USP15 belongs to the ubiquitin specific protease (USP) family of deubiquitinating enzymes which has a vital role in ubiquitin-dependent processes through polyubiquitin chain disassembly and hydrolysis of ubiquitin-substrate bonds. USP15 connects with the COP9 signalosome, and takes part in transforming growth factor beta signalling through deubiquitination of receptor-activated SMAD transcription factors. Alternatively spliced transcript variants encoding multiple isoforms of this gene are known, and a pseudo gene of USP15 is sited on the long arm of chromosome 2.

USP46 is a part of a large family of cysteine proteases that function as deubiquitinating enzymes which interacts with WDR48 to have a high activity. USP46 operates by mediating the deubiquitination of GAD1/GAD67.

Urinary-Trypsin Inhibitor is a glucoprotein proteinase inhibitor which inhibits the activity of trypsin, chymotrypsin, lactate, lipase, hyaluronidase and various pancreatic enzymes. Ulinastatin is effective for acute pancreatitis, chronic recurrent pancreatitis and hemorrhagic, traumatic and endotoxic shocks. Ulinastatin is has strong inhibition effect to various protease, sugar and fat hydrolase. Ulinastatin precursor is proteolytically processed into distinct functioning proteins. Urinary trypsin inhibitor belongs to the superfamily of Kunitz-type protease inhibitors and plays an important role in many physiological and pathological processes. Uristatin gene is located on chromosome 9 in a cluster of lipocalin genes.
High levels of Ulinastatin secretion is an early marker of renal tubular involvement and has radical scavenging activity. Bikunin localizes cell membrane.
Free uristatin and bikunin pass readily into urine and are primarily bound to heavy chains that constitute the proinhibitor form in plasma. UTI has a calculated Mw of approx. 20kDa and 40kDa by SDS-PAGE analysis.
Ulinastatin particularly interacts with ORF3 protein of hepatitis E virus and in charge for enhancing alpha microglobulin export from the hepatocyte.

rRNA-processing protein UTP23 homolog (UTP23) is a small subunit (SSU) processome component. The SSU processome is a complex involved in ribosome biogenesis and essential for pre-18S rRNA maturation. UTP23 is vital for the first 3 cleavage steps in 18S rRNA maturation. Furthermore, single-point mutations in the conserved putative active site of Utp24 but not Utp23 annul its function in ribosome biogenesis.

Ubiquitously-expressed transcript (UXT) is a member of the UXT family. UXT serves as a cofactor which modulates androgen receptor-dependent transcription, and also has a crucial role in tumor necrosis factor-induced apoptosis. UXT gene expression has a role in tumorigenesis. UXT is ubiquitous expressed: it is expressed in prostate epithelial cells, overexpressed in a number of tumor tissues. The highest levels are found in the heart, skeletal muscle, pancreas, kidney, liver, adrenal gland, peripheral blood leukocytes, lymph node, prostate, and thyroid and the lowest levels in bladder and uterus.

Synaptobrevin 1(Vehicle-associated membrane, VAMP1) is one of the key proteins in the SNARE complex which is involved in regulated exocytosis. Synaptobrevin1 binds to t-SNAREs, syntaxin (STX) and SNAP25, after the fusion of synaptic vesicles to plasma membrane.

Synaptobrevin 2 which is an 18 kDa integral membrane protein localized to the cytoplasmic surface of synaptic vesicle, consists of a proline-rich N-terminal region, a highly conserved hydrophilic domain, followed by a transmembrane anchor and a C-terminal. Synaptobrevin 2 is predominantly expressed in Langerhans islets and glomerular cells. The N-terminal domain of the protein (residues 1-89) forms a specific SNARE complex with the target membrane-associated t- or Q-SNAREs syntaxin 1 and SNAP-25.

Synaptobrevin 2 which is an 18 kDa integral membrane protein localized to the cytoplasmic surface of synaptic vesicle, consists of a proline-rich N-terminal region, a highly conserved hydrophilic domain, followed by a transmembrane anchor and a C-terminal. Synaptobrevin 2 is predominantly expressed in Langerhans islets and glomerular cells. The N-terminal domain of the protein (residues 1-89) forms a specific SNARE complex with the target membrane-associated t- or Q-SNAREs syntaxin 1 and SNAP-25.

Synaptobrevin-2 or VAMP2 is a protein that has a proline-rich N-terminal part, highly conserved hydrophilic domain, a transmembrane anchor and a C-terminal.VAMP2 found in the transmembrane region of the cell, in the cytoplasmic surface of the synaptic vesicle. The protein is mainly found in the Langerhans islets in the pancreas and glomerular cells in the kidney. A SNARE complex is created within the protein’s N-terminal domain and the target membrane-associated T.

Synaptobrevin 2 which is an 18 kDa integral membrane protein localized to the cytoplasmic surface of synaptic vesicle, consists of a proline-rich N-terminal region, a highly conserved hydrophilic domain, followed by a transmembrane anchor and a C-terminal. Synaptobrevin 2 is predominantly expressed in Langerhans islets and glomerular cells. The N-terminal domain of the protein (residues 1-89) forms a specific SNARE complex with the target membrane-associated t- or Q-SNAREs syntaxin 1 and SNAP-25.

VAMP3 is present in recycling endosomes and endosome-derived vesicles. VAMP3 has been implicated in recycling of transferrin receptors to the plasma membrane, secretion of alpha-granules in platelets, recycling of T-cell receptors to the immunological synapses, and membrane trafficking during cell migration. VAMP-3 is present in human platelets and necessary for granule secretion. Synaptobrevins are the main components of a protein complex involved in the docking and/or fusion of synaptic vesicles with the presynaptic membrane. VAMP3 high homology to other VAMPs in its broad tissue distribution and subcellular localization is shown to be the human equivalent of the rodent cellubrevin. In platelets the protein resides on a compartment that is not mobilized to the plasma membrane on calcium or thrombin stimulation.

VAMP3 is present in recycling endosomes and endosome-derived vesicles. VAMP3 has been implicated in recycling of transferrin receptors to the plasma membrane, secretion of alpha-granules in platelets, recycling of T-cell receptors to the immunological synapses, and membrane trafficking during cell migration. VAMP-3 is present in human platelets and necessary for granule secretion. Synaptobrevins are the main components of a protein complex involved in the docking and/or fusion of synaptic vesicles with the presynaptic membrane. VAMP3 high homology to other VAMPs in its broad tissue distribution and subcellular localization is shown to be the human equivalent of the rodent cellubrevin. In platelets the protein resides on a compartment that is not mobilized to the plasma membrane on calcium or thrombin stimulation.

VAMP4 belongs to the synaptobrevin family who are involved in docking and/or fusion of vesicles with cell membrane. VAMP4 is enriched in the trans-Golgi network and may be a factor in the trans-Golgi network-to-endosome transport. VAMP4 is involved in the pathway which functions to eliminate an inhibitor (most likely synaptotagmin-4) of calcium-triggered exocytosis during the maturation of secretory granules. Synaptobrevins, syntaxins, and SNAP25 are the chief components of a protein complex involved in the docking and/or fusion of synaptic vesicles with the presynaptic membrane.