Gene Symbol: Vamp2
Description: vesicle-associated membrane protein 2
Alias: RATVAMPB, RATVAMPIR, SYB, Syb2, vesicle-associated membrane protein 2, Synaptobrevin 2 (vesicle-associated membrane protein VAMP-2), VAMP-2, Vesicle-associated membrane protein (synaptobrevin 2), synaptobrevin-2
Species: rat
Products:     Vamp2

Top Publications

  1. Procino G, Barbieri C, Tamma G, De Benedictis L, Pessin J, Svelto M, et al. AQP2 exocytosis in the renal collecting duct -- involvement of SNARE isoforms and the regulatory role of Munc18b. J Cell Sci. 2008;121:2097-106 pubmed publisher
    ..Both VAMP2 and VAMP3 were associated with immunoisolated AQP2 vesicles, whereas syntaxin 3 (Stx3), SNAP23 and Munc18 were ..
  2. Williams D, Pessin J. Mapping of R-SNARE function at distinct intracellular GLUT4 trafficking steps in adipocytes. J Cell Biol. 2008;180:375-87 pubmed publisher
    ..Using this approach, we confirm the requirement of VAMP2 and VAMP7 for insulin and osmotic shock trafficking from the vesicle storage sites, respectively, and fusion with ..
  3. Asano Miyoshi M, Hamamichi R, Emori Y. Synaptophysin as a probable component of neurotransmission occurring in taste receptor cells. J Mol Histol. 2009;40:59-70 pubmed publisher
    ..These results suggest that the taste receptor cells have a neurotransmission system involving synaptophysin, which occurs alternatively or additionally to a recently shown hemichannel system...
  4. Lvov A, Chikvashvili D, Michaelevski I, Lotan I. VAMP2 interacts directly with the N terminus of Kv2.1 to enhance channel inactivation. Pflugers Arch. 2008;456:1121-36 pubmed publisher
    ..We report here that Kv2.1 interacts with VAMP2, the vesicular SNARE partner that is also present at high concentration in neuronal plasma membrane...
  5. Schwenk R, Dirkx E, Coumans W, Bonen A, Klip A, Glatz J, et al. Requirement for distinct vesicle-associated membrane proteins in insulin- and AMP-activated protein kinase (AMPK)-induced translocation of GLUT4 and CD36 in cultured cardiomyocytes. Diabetologia. 2010;53:2209-19 pubmed publisher
    ..demonstrated to be necessary for both GLUT4 and CD36 translocation, either specifically in insulin-treated cells (VAMP2, VAMP5) or in oligomycin/contraction-treated cells (VAMP3)...
  6. Raptis A, Torrejón Escribano B, Gómez de Aranda I, Blasi J. Distribution of synaptobrevin/VAMP 1 and 2 in rat brain. J Chem Neuroanat. 2005;30:201-11 pubmed
    ..isoforms are involved in calcium-dependent synaptic vesicle exocytosis, synaptobrevin/VAMP 1 and synaptobrevin/VAMP 2. However, the functional significance of these two highly homologous isoforms remains to be elucidated...
  7. Pennuto M, Dunlap D, Contestabile A, Benfenati F, Valtorta F. Fluorescence resonance energy transfer detection of synaptophysin I and vesicle-associated membrane protein 2 interactions during exocytosis from single live synapses. Mol Biol Cell. 2002;13:2706-17 pubmed
    To investigate the molecular interactions of synaptophysin I and vesicle-associated membrane protein 2 (VAMP2)/synaptobrevin II during exocytosis, we have used time-lapse videomicroscopy to measure fluorescence resonance energy transfer ..
  8. Rose A, Jeppesen J, Kiens B, Richter E. Effects of contraction on localization of GLUT4 and v-SNARE isoforms in rat skeletal muscle. Am J Physiol Regul Integr Comp Physiol. 2009;297:R1228-37 pubmed publisher
    ..b>VAMP2, VAMP3, VAMP5, and VAMP7 were enriched in immunoprecipitated GLUT4 vesicles...
  9. Tokumaru H, Shimizu Okabe C, Abe T. Direct interaction of SNARE complex binding protein synaphin/complexin with calcium sensor synaptotagmin 1. Brain Cell Biol. 2008;36:173-89 pubmed publisher
    ..We propose that synaphin recruits synaptotagmin 1 to the SNARE-based fusion complex and synergistically functions with synaptotagmin 1 in mediating fast synaptic vesicle exocytosis. ..

More Information


  1. Schoch S, Deak F, Königstorfer A, Mozhayeva M, Sara Y, Sudhof T, et al. SNARE function analyzed in synaptobrevin/VAMP knockout mice. Science. 2001;294:1117-22 pubmed
    ..In the absence of synaptobrevin 2, spontaneous synaptic vesicle fusion and fusion induced by hypertonic sucrose were decreased approximately 10-..
  2. Sutton R, Fasshauer D, Jahn R, Brunger A. Crystal structure of a SNARE complex involved in synaptic exocytosis at 2.4 A resolution. Nature. 1998;395:347-53 pubmed
    ..These characteristics may be important for membrane fusion and for the binding of regulatory factors affecting neurotransmission. ..
  3. Ernst J, Brunger A. High resolution structure, stability, and synaptotagmin binding of a truncated neuronal SNARE complex. J Biol Chem. 2003;278:8630-6 pubmed
    ..The truncated SNARE complex is monomeric, and it retains binding to synaptotagmin I. ..
  4. Pennuto M, Bonanomi D, Benfenati F, Valtorta F. Synaptophysin I controls the targeting of VAMP2/synaptobrevin II to synaptic vesicles. Mol Biol Cell. 2003;14:4909-19 pubmed
    ..Interestingly, the proteins displayed a diffuse component of distribution along the axon. In addition, VAMP2 was found to travel in vesicles that constitutively fuse with the plasma membrane...
  5. Singh B, Lockwich T, Bandyopadhyay B, Liu X, Bollimuntha S, Brazer S, et al. VAMP2-dependent exocytosis regulates plasma membrane insertion of TRPC3 channels and contributes to agonist-stimulated Ca2+ influx. Mol Cell. 2004;15:635-46 pubmed
    ..Here we demonstrate that TRPC3-N terminus interacts with VAMP2 and alphaSNAP...
  6. Pobbati A, Stein A, Fasshauer D. N- to C-terminal SNARE complex assembly promotes rapid membrane fusion. Science. 2006;313:673-6 pubmed
    ..the soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) syntaxin 1, SNAP-25, and synaptobrevin 2 is thought to be the driving force for the exocytosis of synaptic vesicles...
  7. Wang L, Peng R, Hu X, Gao Y, Wang S, Zhao L, et al. Abnormality of synaptic vesicular associated proteins in cerebral cortex and hippocampus after microwave exposure. Synapse. 2009;63:1010-6 pubmed publisher
    ..The perturbation could induce the deposit of synaptic vesicle, which might be relative to the dysfunction of the synaptic transmission, even the cognition deficit. ..
  8. Yao H, Zhou K, Yan D, Li M, Wang Y. The Kv2.1 channels mediate neuronal apoptosis induced by excitotoxicity. J Neurochem. 2009;108:909-19 pubmed publisher
    ..1 membrane translocation is regulated by a soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent vesicular trafficking mechanism and is responsible for neuronal cell death induced by chronic loss of K(+). ..
  9. Che Y, Yamashita T, Tohyama M. Changes in mRNA for VAMPs following facial nerve transection. J Chem Neuroanat. 2002;24:147-52 pubmed
    ..Signals for VAMP2 and -3 mRNAs in the facial nucleus were increased from 3 to 28 days after axotomy...
  10. Li H, Alavian K, Lazrove E, Mehta N, Jones A, Zhang P, et al. A Bcl-xL-Drp1 complex regulates synaptic vesicle membrane dynamics during endocytosis. Nat Cell Biol. 2013;15:773-85 pubmed publisher
    ..Mutagenesis studies suggest that formation of the Bcl-xL-Drp1 complex is necessary for the enhanced rate of vesicle endocytosis produced by Bcl-xL, thus providing a mechanism for presynaptic plasticity. ..
  11. Takamori S, Holt M, Stenius K, Lemke E, Gr Nborg M, Riedel D, et al. Molecular anatomy of a trafficking organelle. Cell. 2006;127:831-46 pubmed publisher
  12. Nevins A, Thurmond D. A direct interaction between Cdc42 and vesicle-associated membrane protein 2 regulates SNARE-dependent insulin exocytosis. J Biol Chem. 2005;280:1944-52 pubmed
    ..interactions among the target SNARE protein Syntaxin 1A and the vesicle-associated membrane SNARE protein (VAMP2) with Cdc42 and compared these structural interactions with their functional importance to glucose-stimulated ..
  13. Yun H, Park J, Ho D, Kim H, Kim C, Oh H, et al. LRRK2 phosphorylates Snapin and inhibits interaction of Snapin with SNAP-25. Exp Mol Med. 2013;45:e36 pubmed publisher
    ..Combined, these data suggest that LRRK2 may regulate neurotransmitter release via control of Snapin function by inhibitory phosphorylation...
  14. Antonin W, Riedel D, von Mollard G. The SNARE Vti1a-beta is localized to small synaptic vesicles and participates in a novel SNARE complex. J Neurosci. 2000;20:5724-32 pubmed
    ..These data suggest that Vti1a-beta does not function in exocytosis but in a separate SNARE complex in a membrane fusion step during recycling or biogenesis of synaptic vesicles...
  15. Wang P, Howard M, Zhang H, Chintagari N, Bell A, Jin N, et al. Characterization of VAMP-2 in the lung: implication in lung surfactant secretion. Cell Biol Int. 2012;36:785-91 pubmed publisher
    ..Functionally, the cytoplasmic domain of VAMP-2, but not VAMP-8 inhibited surfactant secretion in type II cells. We suggest that VAMP-2 is the v-SNARE (vesicle SNARE) involved in regulated surfactant secretion. ..
  16. Gu Y, Chiu S, Liu B, Wu P, Delannoy M, Lin D, et al. Differential vesicular sorting of AMPA and GABAA receptors. Proc Natl Acad Sci U S A. 2016;113:E922-31 pubmed publisher
    ..The insertion of AMPA receptors requires SNAP25-syntaxin1A/B-VAMP2 complexes, whereas insertion of GABAA receptors relies on SNAP23-syntaxin1A/B-VAMP2 complexes...
  17. Marcet Palacios M, Odemuyiwa S, Coughlin J, Garofoli D, Ewen C, Davidson C, et al. Vesicle-associated membrane protein 7 (VAMP-7) is essential for target cell killing in a natural killer cell line. Biochem Biophys Res Commun. 2008;366:617-23 pubmed
    ..Thus, targeting VAMP-7 expression specifically with siRNA, following transplantation, may be a viable strategy for preventing NK cell-mediated transplant rejection, in vivo. ..
  18. Jakhanwal S, Lee C, Urlaub H, Jahn R. An activated Q-SNARE/SM protein complex as a possible intermediate in SNARE assembly. EMBO J. 2017;36:1788-1802 pubmed publisher
    ..Moreover, the complex is resistant to disassembly by NSF Based on these findings, we consider the ternary complex as a strong candidate for a physiological intermediate in SNARE assembly. ..
  19. Jagadish M, Fernandez C, Hewish D, Macaulay S, Gough K, Grusovin J, et al. Insulin-responsive tissues contain the core complex protein SNAP-25 (synaptosomal-associated protein 25) A and B isoforms in addition to syntaxin 4 and synaptobrevins 1 and 2. Biochem J. 1996;317 ( Pt 3):945-54 pubmed
    ..Furthermore, we have confirmed the presence of syntaxin 4 in fat and of synaptobrevin 2 in skeletal muscle by PCR amplification and Southern hybridization analysis...
  20. Vassilopoulos S, Esk C, Hoshino S, Funke B, Chen C, Plocik A, et al. A role for the CHC22 clathrin heavy-chain isoform in human glucose metabolism. Science. 2009;324:1192-6 pubmed publisher
    ..Thus, CHC22-dependent membrane trafficking constitutes a species-restricted pathway in human muscle and fat with potential implications for type 2 diabetes. ..
  21. Maienschein V, Marxen M, Volknandt W, Zimmermann H. A plethora of presynaptic proteins associated with ATP-storing organelles in cultured astrocytes. Glia. 1999;26:233-44 pubmed
    ..Our data suggest that messenger substances may be released from cultured astrocytes via receptor-mediated, Ca2+-dependent exocytosis. ..
  22. Ferlito M, Fulton W, Zauher M, Marban E, Steenbergen C, Lowenstein C. VAMP-1, VAMP-2, and syntaxin-4 regulate ANP release from cardiac myocytes. J Mol Cell Cardiol. 2010;49:791-800 pubmed publisher
    ..Our data suggest that three specific SNAREs regulate cardiac myocyte exocytosis of ANP. Pathways that modify the exocytic machinery may influence natriuresis and blood pressure. ..
  23. Ke B, Oh E, Thurmond D. Doc2beta is a novel Munc18c-interacting partner and positive effector of syntaxin 4-mediated exocytosis. J Biol Chem. 2007;282:21786-97 pubmed
    ..All changes in secretion correlated with parallel alterations in VAMP2 granule docking with Syntaxin 4...
  24. Manca P, Mameli O, Caria M, Torrej n Escribano B, Blasi J. Distribution of SNAP25, VAMP1 and VAMP2 in mature and developing deep cerebellar nuclei after estrogen administration. Neuroscience. 2014;266:102-15 pubmed publisher
    Synaptosomal-associated protein of 25kDa (SNAP25), vesicle-associated membrane protein 1 (VAMP1) and 2 (VAMP2) are components of soluble N-ethylmaleimide-sensitive fusion attachment protein receptors (SNARE) complex which is involved in ..
  25. Kioumourtzoglou D, Gould G, Bryant N. Insulin stimulates syntaxin4 SNARE complex assembly via a novel regulatory mechanism. Mol Cell Biol. 2014;34:1271-9 pubmed publisher the plasma membrane is mediated by formation of functional SNARE complexes containing syntaxin4, SNAP23, and VAMP2. Here we have used an in situ proximity ligation assay to integrate these two observations by demonstrating for ..
  26. Müller H, Kragballe M, Fjorback A, Wiborg O. Differential regulation of the serotonin transporter by vesicle-associated membrane protein 2 in cells of neuronal versus non-neuronal origin. PLoS ONE. 2014;9:e97540 pubmed publisher
    ..Here, we report that vesicle-associated membrane protein 2 (VAMP2), a SNARE protein that mediates vesicle fusion with the plasma membrane, interacts with SERT...
  27. Jurado S, Goswami D, Zhang Y, Molina A, Sudhof T, Malenka R. LTP requires a unique postsynaptic SNARE fusion machinery. Neuron. 2013;77:542-58 pubmed publisher
    ..In contrast, the R-SNARE protein synaptobrevin-2/VAMP2 contributes to both regulated and constitutive AMPAR exocytosis...
  28. Sikorra S, Henke T, Galli T, Binz T. Substrate recognition mechanism of VAMP/synaptobrevin-cleaving clostridial neurotoxins. J Biol Chem. 2008;283:21145-52 pubmed publisher
    ..The data show that, similar to the SNAP-25 proteolyzing BoNT/A and E, VAMP/synaptobrevin-specific clostridial neurotoxins also initiate substrate interaction, employing an exosite located N-terminal of the scissile peptide bond. ..
  29. Ngatchou A, Kisler K, Fang Q, Walter A, Zhao Y, Bruns D, et al. Role of the synaptobrevin C terminus in fusion pore formation. Proc Natl Acad Sci U S A. 2010;107:18463-8 pubmed publisher
    Neurotransmitter release is mediated by the SNARE proteins synaptobrevin II (sybII, also known as VAMP2), syntaxin, and SNAP-25, generating a force transfer to the membranes and inducing fusion pore formation...
  30. Felkl M, Leube R. Interaction assays in yeast and cultured cells confirm known and identify novel partners of the synaptic vesicle protein synaptophysin. Neuroscience. 2008;156:344-52 pubmed publisher
  31. Borisovska M, Zhao Y, Tsytsyura Y, Glyvuk N, Takamori S, Matti U, et al. v-SNAREs control exocytosis of vesicles from priming to fusion. EMBO J. 2005;24:2114-26 pubmed
    ..We demonstrate that dynamics of fusion pore dilation are regulated by v-SNAREs, indicating their action throughout exocytosis from priming to fusion of vesicles. ..
  32. Caceres P, Mendez M, Ortiz P. Vesicle-associated membrane protein 2 (VAMP2) but Not VAMP3 mediates cAMP-stimulated trafficking of the renal Na+-K+-2Cl- co-transporter NKCC2 in thick ascending limbs. J Biol Chem. 2014;289:23951-62 pubmed publisher
    ..Here we report that NKCC2 co-immunoprecipitates with VAMP2 in rat TALs, and they co-localize in discrete domains at the apical surface...
  33. St Denis J, Cabaniols J, Cushman S, Roche P. SNAP-23 participates in SNARE complex assembly in rat adipose cells. Biochem J. 1999;338 ( Pt 3):709-15 pubmed
    ..In addition, we demonstrate for the first time the participation of SNAP-23, along with syntaxin 4 and VAMP2/3, in the formation of 20S SNARE complexes prepared using rat adipose cell membranes and recombinant alpha-SNAP ..
  34. Kepner E, Yoder S, Oh E, Kalwat M, Wang Z, Quilliam L, et al. Cool-1/?PIX functions as a guanine nucleotide exchange factor in the cycling of Cdc42 to regulate insulin secretion. Am J Physiol Endocrinol Metab. 2011;301:E1072-80 pubmed publisher
  35. Ortiz P. cAMP increases surface expression of NKCC2 in rat thick ascending limbs: role of VAMP. Am J Physiol Renal Physiol. 2006;290:F608-16 pubmed
    ..min(-1).mm(-1); not significant). We concluded that cAMP increases NKCC2 surface expression by a mechanism involving VAMP and that NKCC2 trafficking to the apical membrane is involved in the stimulation of TAL NaCl absorption by cAMP. ..
  36. Yamamoto Y, Fujikura K, Sakaue M, Okimura K, Kobayashi Y, Nakamura T, et al. The tail domain of tomosyn controls membrane fusion through tomosyn displacement by VAMP2. Biochem Biophys Res Commun. 2010;399:24-30 pubmed publisher
    ..Cumulative biochemical results suggest that the tomosyn-SNARE complex is so tight that VAMP2 cannot displace tomosyn...
  37. Fdez E, Jowitt T, Wang M, Rajebhosale M, Foster K, Bella J, et al. A role for soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex dimerization during neurosecretion. Mol Biol Cell. 2008;19:3379-89 pubmed publisher
    ..of cytosolic SNARE complexes are in apposition, and it involves residues from the vesicle-associated SNARE synaptobrevin 2 that lie close to the cytosol-membrane interface within the full-length protein...
  38. Cosen Binker L, Binker M, Wang C, Hong W, Gaisano H. VAMP8 is the v-SNARE that mediates basolateral exocytosis in a mouse model of alcoholic pancreatitis. J Clin Invest. 2008;118:2535-51 pubmed publisher
    ..These findings indicate that VAMP8 is the ZG-SNARE that mediates basolateral exocytosis in alcoholic pancreatitis and that VAMP8 is critical for ZG-ZG homotypic fusion. ..
  39. Deng A, Rapp J. Locus for the inducible, but not a constitutive, nitric oxide synthase cosegregates with blood pressure in the Dahl salt-sensitive rat. J Clin Invest. 1995;95:2170-7 pubmed
    ..In F2(S x MNS) functionally variant alleles at both QTL influence blood pressure, but in F2(S x WKY) only the QTL marked by Nos2 is segregating alleles influencing blood pressure. ..
  40. Larance M, Ramm G, James D. The GLUT4 code. Mol Endocrinol. 2008;22:226-33 pubmed
    ..Many are now taking on this challenge. ..
  41. He S, Yang J. Maturation of neurotransmission in the developing rat cochlea: immunohistochemical evidence from differential expression of synaptophysin and synaptobrevin 2. Eur J Histochem. 2011;55:e2 pubmed publisher
    Synaptophysin and synaptobrevin 2 associate closely with packaging and storage of synaptic vesicles and transmitter release, and both play important roles in the development of rat cochlea...
  42. Takuma T, Shitara A, Arakawa T, Okayama M, Mizoguchi I, Tajima Y. Isoproterenol stimulates transient SNAP23-VAMP2 interaction in rat parotid glands. FEBS Lett. 2013;587:583-9 pubmed publisher
    ..When SNARE complexes were immunoprecipitated by anti-SNAP23, the coprecipitation of VAMP2 was significantly increased in response to ISO and/or CyD, although the coprecipitation of VAMP8 or syntaxin 4 was ..
  43. Roy R, Laage R, Langosch D. Synaptobrevin transmembrane domain dimerization-revisited. Biochemistry. 2004;43:4964-70 pubmed
    ..Thus, our present results corroborate that homodimerization of synaptobrevin is mediated by its transmembrane segment. ..
  44. Fasshauer D, Eliason W, Brunger A, Jahn R. Identification of a minimal core of the synaptic SNARE complex sufficient for reversible assembly and disassembly. Biochemistry. 1998;37:10354-62 pubmed
    ..These conserved biophysical properties may thus be of fundamental importance in the mechanism of membrane fusion. ..
  45. Chen X, Tomchick D, Kovrigin E, Arac D, Machius M, Sudhof T, et al. Three-dimensional structure of the complexin/SNARE complex. Neuron. 2002;33:397-409 pubmed
    ..These results suggest that complexin stabilizes the fully assembled SNARE complex as a key step that enables the exquisitely high speed of Ca(2+)-evoked neurotransmitter release. ..
  46. Mayer P, Huang N, Dewey C, Dries D, Zhang H, Yu G. Expression, localization, and biochemical characterization of nicotinamide mononucleotide adenylyltransferase 2. J Biol Chem. 2010;285:40387-96 pubmed publisher
    ..These studies show that Nmnat2 is a neuronal protein peripherally attached to membranes via palmitoylation and suggest that Nmnat2 is transported to synaptic terminals via an endosomal pathway. ..
  47. Elferink L, Trimble W, Scheller R. Two vesicle-associated membrane protein genes are differentially expressed in the rat central nervous system. J Biol Chem. 1989;264:11061-4 pubmed
    ..Both VAMP transcripts are expressed differentially in the rat central nervous system. Whereas VAMP-2 is more highly expressed in the whole brain, VAMP-1 is expressed at a higher level in the spinal cord. ..
  48. Bose A, Guilherme A, Robida S, Nicoloro S, Zhou Q, Jiang Z, et al. Glucose transporter recycling in response to insulin is facilitated by myosin Myo1c. Nature. 2002;420:821-4 pubmed
    ..Thus, myosin Myo1c functions in a PI(3)K-independent insulin signalling pathway that controls the movement of intracellular GLUT4-containing vesicles to the plasma membrane. ..
  49. Quetglas S, Iborra C, Sasakawa N, De Haro L, Kumakura K, Sato K, et al. Calmodulin and lipid binding to synaptobrevin regulates calcium-dependent exocytosis. EMBO J. 2002;21:3970-9 pubmed
    ..release involves the assembly of a heterotrimeric SNARE complex composed of the vesicle protein synaptobrevin (VAMP 2) and two plasma membrane partners, syntaxin 1 and SNAP-25...
  50. Perez Branguli F, Mishra H, Prots I, Havlicek S, Kohl Z, Saul D, et al. Dysfunction of spatacsin leads to axonal pathology in SPG11-linked hereditary spastic paraplegia. Hum Mol Genet. 2014;23:4859-74 pubmed publisher
    ..Understanding the cellular functions of spatacsin will allow deciphering mechanisms of motor cortex dysfunction in autosomal-recessive hereditary spastic paraplegia. ..
  51. Vennekate W, Schröder S, Lin C, van den Bogaart G, Grunwald M, Jahn R, et al. Cis- and trans-membrane interactions of synaptotagmin-1. Proc Natl Acad Sci U S A. 2012;109:11037-42 pubmed publisher
    ..We conclude that trans-interactions of synaptotagmin considered to be essential for its function are controlled by a delicate balance between cis- and trans-binding, which may play an important modulatory role in synaptic transmission. ..
  52. Gitler D, Xu Y, Kao H, Lin D, Lim S, Feng J, et al. Molecular determinants of synapsin targeting to presynaptic terminals. J Neurosci. 2004;24:3711-20 pubmed
    ..Domain D inhibited targeting, but this inhibition was overcome by domain E. Thus, multiple intermolecular and intramolecular interactions are required for synapsins to target to presynaptic terminals. ..
  53. Zaid H, Antonescu C, Randhawa V, Klip A. Insulin action on glucose transporters through molecular switches, tracks and tethers. Biochem J. 2008;413:201-15 pubmed publisher