Abstract:rsec6 and rsec8 are two components of a 17S complex in mammalian brain that is homologous to the yeast 834 kDa Sec6/8/15 complex which is essential for exocytosis. Purification and partial amino acid sequencing of the mammalian rsec6/8 complex reveals that it is composed of eight novel proteins with a combined molecular weight of 743 kDa. The complex is broadly expressed in brain and displays a plasma membrane localization in nerve terminals. Membrane associated rsec6/8 complex coimmunoprecipitates with syntax… Show more
“…Hybridoma production, ELISA and Western blot screening, subcloning, and expansion were carried out as described previously (Hsu et al, 1996). Goat polyclonal antibodies against syntaxin 17 were prepared by immunization with bacterially expressed rat syntaxin 17 produced as described above.…”
Section: Antibodiesmentioning
confidence: 99%
“…Individual protein bands were cut out and subjected to in-gel proteolysis by trypsin. Aliquots of the digested peptides were subjected to mass spectrometry, and remaining peptide mixtures were fractionated by HPLC and microsequenced as described previously (Hsu et al, 1996). In addition, the identities of the precipitated proteins were verified by Western blot analyses.…”
Section: Immunoprecipitation Experiments and Protein Sequencingmentioning
The endoplasmic reticulum (ER) consists of subcompartments that have distinct protein constituents, morphological appearances, and functions. To understand the mechanisms that regulate the intricate and dynamic organization of the endoplasmic reticulum, it is important to identify and characterize the molecular machinery involved in the assembly and maintenance of the different subcompartments. Here we report that syntaxin 17 is abundantly expressed in steroidogenic cell types and specifically localizes to smooth membranes of the ER. By immunoprecipitation analyses, syntaxin 17 exists in complexes with a syntaxin regulatory protein, rsly1, and/or two intermediate compartment SNARE proteins, rsec22b and rbet1. Furthermore, we found that syntaxin 17 is anchored to the smooth endoplasmic reticulum through an unusual mechanism, requiring two adjacent hydrophobic domains near its carboxyl terminus. Converging lines of evidence indicate that syntaxin 17 functions in a vesicle-trafficking step to the smooth-surfaced tubular ER membranes that are abundant in steroidogenic cells.
“…Hybridoma production, ELISA and Western blot screening, subcloning, and expansion were carried out as described previously (Hsu et al, 1996). Goat polyclonal antibodies against syntaxin 17 were prepared by immunization with bacterially expressed rat syntaxin 17 produced as described above.…”
Section: Antibodiesmentioning
confidence: 99%
“…Individual protein bands were cut out and subjected to in-gel proteolysis by trypsin. Aliquots of the digested peptides were subjected to mass spectrometry, and remaining peptide mixtures were fractionated by HPLC and microsequenced as described previously (Hsu et al, 1996). In addition, the identities of the precipitated proteins were verified by Western blot analyses.…”
Section: Immunoprecipitation Experiments and Protein Sequencingmentioning
The endoplasmic reticulum (ER) consists of subcompartments that have distinct protein constituents, morphological appearances, and functions. To understand the mechanisms that regulate the intricate and dynamic organization of the endoplasmic reticulum, it is important to identify and characterize the molecular machinery involved in the assembly and maintenance of the different subcompartments. Here we report that syntaxin 17 is abundantly expressed in steroidogenic cell types and specifically localizes to smooth membranes of the ER. By immunoprecipitation analyses, syntaxin 17 exists in complexes with a syntaxin regulatory protein, rsly1, and/or two intermediate compartment SNARE proteins, rsec22b and rbet1. Furthermore, we found that syntaxin 17 is anchored to the smooth endoplasmic reticulum through an unusual mechanism, requiring two adjacent hydrophobic domains near its carboxyl terminus. Converging lines of evidence indicate that syntaxin 17 functions in a vesicle-trafficking step to the smooth-surfaced tubular ER membranes that are abundant in steroidogenic cells.
“…Although there is no known mammalian homolog for Bud4p, a counterpart exists for each septin and exocyst subunit. The mammalian exocyst [Sec6-Sec8 (EXOC3-EXOC4) complex] has been co-purified and immunoprecipitated with septins (Hsu et al, 1996;Hsu et al, 1998;Hsu et al, 1999); like its yeast counterpart, it was found to influence polarized vesicle delivery (Hsu et al, 1999). Mammalian septins were individually identified and implicated in cytokinesis, exocytosis, vesicle-targeting and membrane dynamics (Spiliotis and Nelson, 2006;Beites et al, 1999;Trimble, 1999).…”
Polarized secretion is a tightly regulated event generated by conserved, asymmetrically localized multiprotein complexes, and the mechanism(s) underlying its temporal and spatial regulation are only beginning to emerge. Although yeast Iqg1p has been identified as a positional marker linking polarity and exocytosis cues, studies on its mammalian counterpart, IQGAP1, have focused on its role in organizing cytoskeletal architecture, for which the underlying mechanism is unclear. Here, we report that IQGAP1 associates and co-localizes with the exocyst-septin complex, and influences the localization of the exocyst and the organization of septin. We further show that activation of CDC42 GTPase abolishes this association and inhibits secretion in pancreatic β-cells. Whereas the N-terminus of IQGAP1 binds the exocyst-septin complex, enhances secretion and abrogates the inhibition caused by CDC42 or the depletion of IQGAP1, the C-terminus, which binds CDC42, inhibits secretion. Pulse-chase experiments indicate that IQGAP1 influences protein-synthesis rates, thus regulating exocytosis. We propose and discuss a model in which IQGAP1 serves as a conformational switch to regulate exocytosis.
“…Several large protein complexes have been proposed to help target vesicles to a particular membrane domain. The exocyst (sec6/8 complex), composed of eight proteins, is thought to help recruit Golgiderived vesicles to the plasma membrane at the final step of the secretory pathway (Hsu et al, 1996;TerBush et al, 1996;Kee et al, 1997). The multisubunit TRAPP I and Vps52/ 53/54 complexes are believed to serve analogous functions during ER-to-Golgi and endosome-to-Golgi trafficking, respectively (Conibear and Stevens, 2000;Sacher et al, 2001).…”
The multisubunit conserved oligomeric Golgi (COG) complex has been shown previously to be involved in Golgi function in yeast and mammalian tissue culture cells. Despite this broad conservation, several subunits, including Cog5, were not essential for growth and showed only mild effects on secretion when mutated in yeast, raising questions about what functions these COG complex subunits play in the life of the cell. Here, we show that function of the gene four way stop (fws), which encodes the Drosophila Cog5 homologue, is necessary for dramatic changes in cellular and subcellular morphology during spermatogenesis. Loss-of-function mutations in fws caused failure of cleavage furrow ingression in dividing spermatocytes and failure of cell elongation in differentiating spermatids and disrupted the formation and/or stability of the Golgibased spermatid acroblast. Consistent with the lack of a growth defect in yeast lacking Cog5, animals lacking fws function were viable, although males were sterile. Fws protein localized to Golgi structures throughout spermatogenesis. We propose that Fws may directly or indirectly facilitate efficient vesicle traffic through the Golgi to support rapid and extensive increases in cell surface area during spermatocyte cytokinesis and polarized elongation of differentiating spermatids. Our study suggests that Drosophila spermatogenesis can be an effective sensitized genetic system to uncover in vivo functions for proteins involved in Golgi architecture and/or vesicle transport.
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