Staring, a Novel E3 Ubiquitin-Protein Ligase That Targets Syntaxin 1 for Degradation

Abstract

Syntaxin 1 is an essential component of the neurotransmitter release machinery, and regulation of syntaxin 1 expression levels is thought to contribute to the mechanism underlying learning and memory. However, the molecular events that control the degradation of syntaxin 1 remain undefined. Here we report the identification and characterization of a novel RING finger protein, Staring, that interacts with syntaxin 1. Staring is expressed throughout the brain, where it exists in both cytosolic and membrane-associated pools. Staring binds and recruits the brain-enriched E2 ubiquitin-conjugating enzyme UbcH8 to syntaxin 1 and facilitates the ubiquitination and proteasome-dependent degradation of syntaxin 1. These findings suggest that Staring is a novel E3 ubiquitin-protein ligase that targets syntaxin 1 for degradation by the ubiquitin-proteasome pathway. Syntaxin 1 is an essential component of the neurotransmitter release machinery, and regulation of syntaxin 1 expression levels is thought to contribute to the mechanism underlying learning and memory. However, the molecular events that control the degradation of syntaxin 1 remain undefined. Here we report the identification and characterization of a novel RING finger protein, Staring, that interacts with syntaxin 1. Staring is expressed throughout the brain, where it exists in both cytosolic and membrane-associated pools. Staring binds and recruits the brain-enriched E2 ubiquitin-conjugating enzyme UbcH8 to syntaxin 1 and facilitates the ubiquitination and proteasome-dependent degradation of syntaxin 1. These findings suggest that Staring is a novel E3 ubiquitin-protein ligase that targets syntaxin 1 for degradation by the ubiquitin-proteasome pathway. Modulation of protein degradation is a major mechanism by which cells regulate the expression levels of specific proteins and consequently the cellular processes that these proteins participate in (1Schwartz A.L. Ciechanover A. Annu. Rev. Med. 1999; 50: 57-74Crossref PubMed Scopus (379) Google Scholar, 2Ciechanover A. Isr. Med. Assoc. J. 2001; 3: 319-327PubMed Google Scholar). The ubiquitin-proteasome pathway plays a crucial role in the degradation of proteins involved in a variety of cellular processes, including differentiation, proliferation, and apoptosis. However, the role of the ubiquitin-proteasome pathway in the degradation of presynaptic proteins remains poorly characterized, despite the presence of ubiquitin at nerve terminals (3Chapman A.P. Courtney S.C. Smith S.J. Rider C.C. Beesley P.W. Biochem. Soc. Trans. 1992; 20: 155SCrossref PubMed Scopus (14) Google Scholar, 4Chapman A.P. Smith S.J. Rider C.C. Beesley P.W. Neurosci. 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Ubiquitination involves a highly specific enzyme cascade in which ubiquitin is first activated by an E1 1The abbreviations used are: E1, ubiquitin-activating enzyme; E2, ubiquitin-conjugating enzyme; E3, ubiquitin-protein ligase; GST, glutathioneS-transferase; DMEM, Dulbecco's modified Eagle's medium; HA, hemagglutinin; SNARE, soluble NSF attachment protein receptors. ubiquitin-activating enzyme and then transferred to an E2 ubiquitin-conjugating enzyme and finally ligated to the substrate by an E3 ubiquitin-protein ligase (1Schwartz A.L. Ciechanover A. Annu. Rev. Med. 1999; 50: 57-74Crossref PubMed Scopus (379) Google Scholar,7Bonifacino J.S. Weissman A.M. Annu. Rev. Cell Dev. Biol. 1998; 14: 19-57Crossref PubMed Scopus (536) Google Scholar, 8Ciechanover A. EMBO J. 1998; 17: 7151-7160Crossref PubMed Scopus (1200) Google Scholar). The E3 ubiquitin-protein ligase plays an essential role in determining the specificity of ubiquitination and subsequent protein degradation. Consistent with this role, it is estimated that an organism such as a human contains over 100 E3 ubiquitin ligases, in contrast to a single E1 ubiquitin-activating enzyme and about a dozen E2 ubiquitin-conjugating enzymes (9Hershko A. Ciechanover A. Annu. Rev. Biochem. 1998; 67: 425-479Crossref PubMed Scopus (6958) Google Scholar). Despite the importance of E3 ubiquitin-protein ligases in specific protein degradation and the estimated presence of more than 100 E3 ligases in the human genome, only a few E3 ligases have been characterized at the molecular level. Syntaxin 1 is a neuronal membrane protein that was originally identified as a binding partner for synaptotagmin and the N-type calcium channel (10Bennett M.K. Calakos N. Scheller R.H. Science. 1992; 257: 255-259Crossref PubMed Scopus (1077) Google Scholar, 11Inoue A. Akagawa K. Biochem. Biophys. Res. Commun. 1992; 187: 1144-1150Crossref PubMed Scopus (43) Google Scholar, 12Yoshida A. Oho C. Omori A. Kuwahara R. Ito T. Takahashi M. J. Biol. Chem. 1992; 267: 24925-24928Abstract Full Text PDF PubMed Google Scholar). It is well established that syntaxin 1 functions as a synaptic t-SNARE to mediate synaptic vesicle exocytosis at nerve terminals (13Rothman J.E. Nature. 1994; 372: 55-63Crossref PubMed Scopus (2011) Google Scholar, 14Jahn R. Sudhof T.C. Annu. Rev. Biochem. 1999; 68: 863-911Crossref PubMed Scopus (1025) Google Scholar, 15Lin R.C. Scheller R.H. Annu. Rev. Cell Dev. Biol. 2000; 16: 19-49Crossref PubMed Scopus (422) Google Scholar). Syntaxin 1 appears early during embryonic development (16Kushima Y. Fujiwara T. Sanada M. Akagawa K. J. Mol. Neurosci. 1997; 8: 19-27Crossref PubMed Scopus (24) Google Scholar, 17Noakes P.G. Chin D. Kim S.S. Liang S. Phillips W.D. J. Comp. Neurol. 1999; 410: 531-540Crossref PubMed Scopus (29) Google Scholar), and its expression level is dramatically up-regulated during synapse formation and brain maturation (16Kushima Y. Fujiwara T. Sanada M. Akagawa K. J. Mol. Neurosci. 1997; 8: 19-27Crossref PubMed Scopus (24) Google Scholar, 17Noakes P.G. Chin D. Kim S.S. Liang S. Phillips W.D. J. Comp. Neurol. 1999; 410: 531-540Crossref PubMed Scopus (29) Google Scholar, 18Miya F. Yamamoto A. Akagawa K. Kawamoto K. Tashiro Y. Cell Struct. Funct. 1996; 21: 525-532Crossref PubMed Scopus (7) Google Scholar, 19Veeranna Grant P. Pant H.C. Dev. Neurosci. 1997; 19: 172-183Crossref PubMed Scopus (22) Google Scholar). Regulation of syntaxin 1 levels may contribute to the mechanism underlying learning and memory, since changes in syntaxin 1 levels have been found to correlate with long term potentiation and various learning and memory behaviors (20Davis S. Rodger J. Hicks A. Mallet J. Laroche S. Eur. J. Neurosci. 1996; 8: 2068-2074Crossref PubMed Scopus (29) Google Scholar, 21Hicks A. Davis S. Rodger J. Helme-Guizon A. Laroche S. Mallet J. Neuroscience. 1997; 79: 329-340Crossref PubMed Scopus (63) Google Scholar, 22Richter-Levin G. Thomas K.L. Hunt S.P. Bliss T.V. Neurosci. Lett. 1998; 251: 41-44Crossref PubMed Scopus (26) Google Scholar). Alteration in syntaxin 1 expression levels has been associated with several neurodegenerative diseases and psychiatric disorders, including schizophrenia, Alzheimer's disease, and Creutzfeldt-Jakob disease (23Gabriel S.M. Haroutunian V. Powchik P. Honer W.G. Davidson M. Davies P. Davis K.L. Arch. Gen. Psychiatry. 1997; 54: 559-566Crossref PubMed Scopus (125) Google Scholar, 24Shimohama S. Kamiya S. Taniguchi T. Akagawa K. Kimura J. Biochem. Biophys. Res. Commun. 1997; 236: 239-242Crossref PubMed Scopus (83) Google Scholar, 25Honer W.G. Falkai P. Young C. Wang T. Xie J. Bonner J., Hu, L. Boulianne G.L. Luo Z. Trimble W.S. Neuroscience. 1997; 78: 99-110Crossref PubMed Scopus (140) Google Scholar, 26Ferrer I. Rivera R. Blanco R. Marti E. Neurobiol. Dis. 1999; 6: 92-100Crossref PubMed Scopus (45) Google Scholar). Despite the importance of the regulation of syntaxin 1 levels in synaptic function and dysfunction, the molecular mechanisms underlying such regulation remain undefined. To identify proteins that regulate syntaxin 1, we carried out a search in rat brain for proteins that interact with syntaxin 1 using yeast two-hybrid screens. Here we report the isolation of a novel syntaxin 1-interacting protein, named Staring, that acts as an E3 ubiquitin-protein ligase to promote the ubiquitination and degradation of syntaxin 1 by the proteasome pathway. The bait plasmid, pPC97-Syntaxin 1, was constructed by subcloning the cytoplasmic domain (amino acids 5–270) of rat syntaxin 1B (27Kwong J. Roundabush F.L. Moore P.H. Montague M. Oldham W., Li, Y. Chin L. Li L. J. Cell Sci. 2000; 113: 2273-2284PubMed Google Scholar) into the pPC97 vector (28Chevray P.M. Nathans D. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 5789-5793Crossref PubMed Scopus (481) Google Scholar, 29Li X.J., Li, S.H. Sharp A.H. Nucifora Jr., F.C. Schilling G. Lanahan A. Worley P. Snyder S.H. Ross C.A. Nature. 1995; 378: 398-402Crossref PubMed Scopus (541) Google Scholar). For the two-hybrid screen, the yeast strain CG-1945 (CLONTECH) was transformed sequentially with pPC97-Syntaxin 1 and a rat hippocampal/cortical two-hybrid cDNA library (29Li X.J., Li, S.H. Sharp A.H. Nucifora Jr., F.C. Schilling G. Lanahan A. Worley P. Snyder S.H. Ross C.A. Nature. 1995; 378: 398-402Crossref PubMed Scopus (541) Google Scholar), using the lithium acetate method (30Chin L.S. Nugent R.D. Raynor M.C. Vavalle J.P. Li L. J. Biol. Chem. 2000; 275: 1191-1200Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). Positive clones were selected on 3-aminotriazole (5 mm; Sigma)-containing medium lacking leucine, tryptophan, and histidine and verified with a filter assay for β-galactosidase activity. Prey plasmids were then recovered and retransformed into yeast with pPC97-Syntaxin 1 or various control to the specificity of the For of Staring, a Staring cDNA the was used to a rat cDNA library in to the J. T. Scholar). The cDNA Staring clones were on both using an molecular J. T. Scholar) were used to and of Staring into the the pPC97 and for yeast two-hybrid the expression and for the of and and the expression and (30Chin L.S. Nugent R.D. Raynor M.C. Vavalle J.P. Li L. J. Biol. Chem. 2000; 275: 1191-1200Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar) for into The expression and were as Y. J. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar). in and and in and were Staring and The were using the as (30Chin L.S. Nugent R.D. Raynor M.C. Vavalle J.P. Li L. J. Biol. Chem. 2000; 275: 1191-1200Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). used in this the and 1 and with of Staring expression was on a rat and a human expression using a Staring cDNA as the J. T. Scholar). For rat were in and to The proteins were transferred and with and binding was by using the of rat brain into and membrane were as (30Chin L.S. Nugent R.D. Raynor M.C. Vavalle J.P. Li L. J. Biol. Chem. 2000; 275: 1191-1200Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). The membrane were to as (30Chin L.S. Nugent R.D. Raynor M.C. Vavalle J.P. Li L. J. Biol. Chem. 2000; 275: 1191-1200Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar), using or proteins or control were on and with rat brain as (30Chin L.S. Nugent R.D. Raynor M.C. Vavalle J.P. Li L. J. Biol. Chem. 2000; 275: 1191-1200Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar, Y. Chin L.S. C. Li L. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). proteins were by in and by and with or cells were with plasmids using as by the Cell were and to as Raynor M.C. Li L. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar), using 1 or control The were recovered by with protein or protein the were by in the and by and cells were with of the 1, and a of Staring that the RING finger cells were with in with or the cells were for with The cells were then and an of protein was using or syntaxin 1 Raynor M.C. Li L. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). were by by with an to to syntaxin 1. cells were with 1 and or vector cells were with or vector To control for the cells were using in a the cells were into of which was used for a single cells in the were and for with The medium was then with of protein for 1 the medium was by with in were then for the in with and the of and as T.C. Chin Li, Y. F.L. Li L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). were then and an of protein was using an were by and by a or cells Staring and syntaxin 1 were for at with the proteasome the the or or were then and the protein of the were by the protein assay of protein was then by and To identify syntaxin 1-interacting we a rat hippocampal/cortical cDNA library by yeast two-hybrid using the cytoplasmic domain of rat syntaxin 1B as to the isolation of several clones a syntaxin 1-interacting protein the of the two-hybrid of the clones was to of a novel protein that we to as Staring it is 1-interacting RING finger protein 1 that Staring interacts with syntaxin and syntaxin 1B with or and t-SNARE that are to the t-SNARE domain of syntaxin 1 T. S.H. S.J. P. K. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar), the of Staring to interact with and the specificity of the 1 of the Staring cDNA that Staring is a protein with a molecular of The the of Staring well to the M. Res. PubMed Scopus Google Scholar) and is by an in the the of Staring with this expressed in cells to a protein with an molecular to that of Staring that the Staring contains the Staring is highly with a of and a of acids over the Staring contains a a in 1, Staring contains and a RING finger at the The RING finger is a binding domain that is found in a of of which have been in K.L. Biochem. Sci. 1996; 21: Full Text PDF PubMed Scopus Google Scholar). that the RING finger may function in protein ubiquitination as a of the E3 ubiquitin-protein ligase K.L. J. Mol. Biol. 2000; PubMed Scopus Google Scholar, C.A. Weissman A.M. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, Annu. Rev. Biochem. 2001; PubMed Scopus Google Scholar). The of rat Staring is to human an protein identified a yeast two-hybrid using protein as bait S. Biochem. Biophys. Res. Commun. 2000; 275: PubMed Scopus Google Scholar). The expression of protein has been on to a of the the human finger protein the presence of Staring as or in a of including and yeast that is the human of rat The human contains a Staring which is by a that is the In C. and appears to only Staring the function of these Staring is the of the yeast Staring was to to including and M. G. C. K. 1999; PubMed Google Scholar, E. M. G. 2001; PubMed Scopus Google Scholar). of the proteins the that these proteins have a domain that is to that of Staring these Staring a highly RING finger at The and domain Staring that Staring is an of Staring expression the presence of a single Staring of The Staring is in brain, and and expressed at levels in and Consistent with this of human Staring expression using a expression that Staring is expressed in various brain as well as and human The of Staring expression that Staring has a role to including To Staring at the protein we in and and in and the and of rat Staring, The and the of Staring are to both Staring and the and the of Staring only the Staring that recognized a single protein of that Staring is the expressed in protein to by or the of Staring that is a that is expressed at levels or expressed at with Staring protein expressed in and cells of these with Staring protein to as well as Staring protein the specificity of these In with the of using the that Staring protein is expressed in the expression levels in and are To the of Staring, of rat brain was into and membrane and then to with Staring was in both and membrane the of Staring in the was more than that in the membrane To the of Staring with the membrane was with or the membrane protein syntaxin 1 that was to by and a of Staring was by these that Staring is associated with To the 1 in yeast in proteins various of Staring were on and used to syntaxin 1 rat brain in the proteins the Staring or the Staring that the domain and Staring was to syntaxin 1. In the protein the domain or was to syntaxin 1, that the 1 is These that the syntaxin of Staring the and In of Staring to contribute to the with syntaxin 1, since the proteins of Staring syntaxin 1 than a of the To Staring with syntaxin 1 in we first using of cells syntaxin 1 and in syntaxin 1 and were by the for the of these proteins in control was to syntaxin 1 or then to the of Staring and syntaxin 1 in rat brain 1 the was to syntaxin 1 and Staring the of 1 at nerve of Staring was with syntaxin 1, that only a of Staring and syntaxin 1 in the 1 These are with that syntaxin 1 interacts with more than a dozen including and R. Sudhof T.C. Annu. Rev. Biochem. 1999; 68: 863-911Crossref PubMed Scopus (1025) Google Scholar, Y. C.A. Sudhof T.C. Nature. PubMed Scopus Google Scholar, A. M. F. N. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, Y. T. T. T. S. Y. A. Scheller R.H. Y. 1998; 20: Full Text Full Text PDF PubMed Scopus Google Scholar, G. V. S. J. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). as by its Staring is to interact with The presence of the RING finger in Staring the that Staring may function as an E3 ubiquitin-protein ligase with a specific E2 ubiquitin-conjugating enzyme Annu. Rev. Biochem. 2001; PubMed Scopus Google Scholar). a first to this Staring was expressed in cells with E2 enzyme or and the of these E2 enzymes with Staring was by The that Staring interacts with a brain-enriched E2 ubiquitin-conjugating enzyme M. T. Y. T. N. Y. S. Y. Cell 1997; 78: PubMed Scopus Google Scholar). In Staring and or These that UbcH8 is the E2 ubiquitin-conjugating enzyme for To Staring interacts with both UbcH8 and syntaxin 1 to a were using of cells with Staring, syntaxin 1, and UbcH8 that syntaxin 1 and UbcH8 with Staring in a that Staring has the to its E2 enzyme UbcH8 to syntaxin 1. we to Staring acts as an E3 ubiquitin-protein ligase to syntaxin 1 by using a well established in ubiquitination assay M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). syntaxin 1 was in cells with ubiquitin in the or presence of Cell were to with an by with an to syntaxin 1 levels of ubiquitin were on syntaxin 1 in the presence of Staring, that Staring the ubiquitination of syntaxin 1. The ubiquitination to the ubiquitinated syntaxin 1 was as a molecular In to the several ubiquitination were which may ubiquitinated syntaxin 1 in as the of the ubiquitination and in have been with ubiquitinated such as and Y. J. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar, Y. K.L. Y. J. Ross C.A. Med. 2001; 1144-1150Crossref PubMed Scopus Google Scholar). The at is a it exists in the control that has ubiquitin. the RING finger is thought to essential for the of a E3 ubiquitin-protein ligase C.A. Weissman A.M. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, Annu. Rev. Biochem. 2001; PubMed Scopus Google Scholar), we the of of the Staring RING finger on the in ubiquitination of syntaxin 1. of Staring that the RING finger was and for its to syntaxin 1 using the ubiquitination assay as The that of the RING finger the of Staring to syntaxin 1, the role of Staring as a E3 ubiquitin-protein of a cellular protein to the degradation of the protein by the proteasome pathway D. Ciechanover A. J. 2000; PubMed Scopus Google Scholar). To ubiquitination of syntaxin 1 its we to the of syntaxin 1 protein in the and presence of in the of syntaxin 1 was in the of the of syntaxin 1 was to in the presence of Staring, that Staring has the to regulate the degradation of syntaxin 1. Consistent with this of the syntaxin 1 protein level by that the expression level of syntaxin 1 was in the presence of Staring as with the syntaxin 1 level in the of Staring the degradation of syntaxin 1 was by a of proteasome function A.L. Cell Biol. 1998; 8: Full Text Full Text PDF PubMed Scopus Google Scholar), by an of these suggest that Staring the degradation of syntaxin 1 by the proteasome pathway. Staring is to regulate the ubiquitination and degradation of syntaxin 1. For these we used human a well characterized that syntaxin 1 and neurotransmitter release K. J. 1997; 68: PubMed Scopus Google Scholar, S. 2001; PubMed Scopus Google Scholar). of Staring in cells the ubiquitination of syntaxin 1, as by the of a molecular syntaxin 1 The of Staring on syntaxin 1 ubiquitination was by the of Staring RING finger that Staring the ubiquitination of syntaxin 1 in a RING In of Staring the of syntaxin 1, as by the in the and presence of Staring The of syntaxin 1 was to by of The of syntaxin 1 was by a in the expression level of syntaxin 1 in the presence of Staring the degradation of syntaxin 1 was by the proteasome by the or these for a role of Staring in the degradation of syntaxin 1 the ubiquitin-proteasome pathway. it is that the ubiquitin-proteasome pathway is involved in synaptic function and A. R.D. K. R. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, A. A.P. A.M. Nature. 2001; PubMed Scopus Google Scholar, 2001; Full Text Full Text PDF PubMed Scopus Google Scholar), is about neuronal protein substrates that are by this pathway. the in the expression levels of presynaptic proteins have been to synaptic and it is and the ubiquitin-proteasome pathway the degradation of these proteins at nerve In this we have identified and characterized Staring, a novel RING finger protein that interacts with syntaxin 1, an essential component of neurotransmitter release suggest that Staring may function as an E3 ubiquitin-protein ligase to promote the ubiquitination and degradation of syntaxin 1 by the proteasome pathway. it is thought that the pathway is used for the degradation of proteins syntaxin 1, the ubiquitin-proteasome pathway is involved in the degradation of cytosolic and However, several the of the ubiquitin-proteasome pathway in the degradation of such as in and the membrane protein 1 G. S. M. T. Dev. 1997; PubMed Scopus Google Scholar, L. 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These findings an role for the ubiquitin-proteasome pathway in the degradation of both cytosolic and membrane proteins at nerve in the is in the of the nerve degradation by the ubiquitin-proteasome pathway may a more for the regulation of presynaptic protein levels at the nerve Staring is a novel of a of RING finger proteins that function as E3 ubiquitin-protein The RING E3 ligases of RING E3 ligases and RING E3 single RING E3 ligase contains the domain and the RING finger in the In a RING E3 ligase is a that contains the RING finger protein as and a protein for substrate Annu. Rev. Biochem. 2001; PubMed Scopus Google Scholar, Ciechanover A. Rev. PubMed Scopus Google Scholar). that Staring is a RING E3 ligase that its domain to substrate syntaxin 1. In to the Staring contains that Staring may and the molecular of the ubiquitin-proteasome pathway, the E3 ubiquitin-protein ligase is the it binds specific substrates and ubiquitination and subsequent degradation. regulation of the substrate and ubiquitination is a major mechanism for of specific protein degradation D. Ciechanover A. J. 2000; PubMed Scopus Google Scholar, Ciechanover A. Rev. PubMed Scopus Google Scholar). in the E3 ubiquitin-protein ligase have been in the of several human diseases Ciechanover A. Rev. PubMed Scopus Google Scholar). For or in the the E3 ubiquitin-protein ligase are a major of 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, T. S. N. Y. S. M. Y. N. Nature. 1998; PubMed Scopus Google Scholar, K. T. T. N. Y. J. Mol. Med. 2001; 79: PubMed Scopus Google Scholar). is expressed in is characterized by a of that of a may involved in the T. S. N. Y. S. M. Y. N. Nature. 1998; PubMed Scopus Google Scholar, K. T. T. N. Y. J. Mol. Med. 2001; 79: PubMed Scopus Google Scholar). to Staring is have found that Staring interacts with the brain-enriched E2 ubiquitin-conjugating enzyme UbcH8 and the ubiquitination and degradation of the protein syntaxin 1. syntaxin 1 levels have been associated with several neurodegenerative it to that syntaxin 1 degradation to the of these of the molecular mechanism that the degradation of presynaptic proteins only of of synaptic such as learning and memory. are to Worley and for the rat hippocampal/cortical cDNA library and the expression for E2 enzymes and and for