1
|
Gerien KS, Zhang S, Russell AC, Zhu YH, Purde V, Wu JQ. Roles of Mso1 and the SM protein Sec1 in efficient vesicle fusion during fission yeast cytokinesis. Mol Biol Cell 2020; 31:1570-1583. [PMID: 32432970 PMCID: PMC7521796 DOI: 10.1091/mbc.e20-01-0067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Membrane trafficking during cytokinesis is essential for the delivery of membrane lipids and cargoes to the division site. However, the molecular mechanisms are still incompletely understood. In this study, we demonstrate the importance of uncharacterized fission yeast proteins Mso1 and Sec1 in membrane trafficking during cytokinesis. Fission yeast Mso1 shares homology with budding yeast Mso1 and human Mint1, proteins that interact with Sec1/Munc18 family proteins during vesicle fusion. Sec1/Munc18 proteins and their interactors are important regulators of SNARE complex formation during vesicle fusion. The roles of these proteins in vesicle trafficking during cytokinesis have been barely studied. Here, we show that fission yeast Mso1 is also a Sec1-binding protein and Mso1 and Sec1 localize to the division site interdependently during cytokinesis. The loss of Sec1 localization in mso1Δ cells results in a decrease in vesicle fusion and cytokinesis defects such as slow ring constriction, defective ring disassembly, and delayed plasma membrane closure. We also find that Mso1 and Sec1 may have functions independent of the exocyst tethering complex on the plasma membrane at the division site. Together, Mso1 and Sec1 play essential roles in regulating vesicle fusion and cargo delivery at the division site during cytokinesis.
Collapse
Affiliation(s)
- Kenneth S Gerien
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210.,Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Sha Zhang
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Alexandra C Russell
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Yi-Hua Zhu
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210
| | - Vedud Purde
- Ohio State Biochemistry Program, The Ohio State University, Columbus, OH 43210.,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210
| | - Jian-Qiu Wu
- Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210.,Department of Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH 43210
| |
Collapse
|
2
|
Zhang Y, Liang Q, Zhang C, Zhang J, Du G, Kang Z. Improving production of Streptomyces griseus trypsin for enzymatic processing of insulin precursor. Microb Cell Fact 2020; 19:88. [PMID: 32284060 PMCID: PMC7155311 DOI: 10.1186/s12934-020-01338-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Accepted: 03/23/2020] [Indexed: 02/07/2023] Open
Abstract
Background Trypsin has many applications in food and pharmaceutical manufacturing. Although commercial trypsin is usually extracted from porcine pancreas, this source carries the risks of infectivity and immunogenicity. Microbial Streptomyces griseus trypsin (SGT) is a prime alternative because it possesses efficient hydrolysis activity without such risks. However, the remarkable hydrolysis efficiency of SGT causes autolysis, and five autolysis sites, R21, R32, K122, R153, and R201, were identified from its autolysate. Results The tbcf (K101A, R201V) mutant was screened by a directed selection approach for improved activity in flask culture (60.85 ± 3.42 U mL−1, increased 1.5-fold). From the molecular dynamics simulation, in the K101A/R201V mutant the distance between the catalytical residues D102 and H57 was shortened to 6.5 Å vs 7.0 Å in the wild type, which afforded the improved specific activity of 1527.96 ± 62.81 U mg−1. Furthermore, the production of trypsin was increased by 302.8% (689.47 ± 6.78 U mL−1) in a 3-L bioreactor, with co-overexpression of chaperones SSO2 and UBC1 in Pichia pastoris. Conclusions SGT protein could be a good source of trypsin for insulin production. As a result of the hydrolysates analysis and direct selection, the activity of the tbcf (K101A, R201V) mutant increased 1.5-fold. Furthermore, the production of trypsin was improved threefold by overexpressing chaperone protein in Pichia pastoris. Future studies should investigate the application of SGT to insulin and pharmaceutical manufacturing.
Collapse
Affiliation(s)
- Yunfeng Zhang
- Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Center for Synthetic Biochemistry, Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technologies, Shenzhen, China
| | - Qixing Liang
- Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Chuanzhi Zhang
- Bio-Pharmaceutical Research Institute Lian Yun Gang Chia Tai Tianqing Pharmaceutical Group Co., Ltd, Lianyungang, Jiangsu, China
| | - Juan Zhang
- Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Guocheng Du
- Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China
| | - Zhen Kang
- Key Laboratory of Industrial Biotechnology, Ministry of Education, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China. .,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.
| |
Collapse
|
3
|
Weber-Boyvat M, Zhao H, Aro N, Yuan Q, Chernov K, Peränen J, Lappalainen P, Jäntti J. A conserved regulatory mode in exocytic membrane fusion revealed by Mso1p membrane interactions. Mol Biol Cell 2012. [PMID: 23197474 PMCID: PMC3564535 DOI: 10.1091/mbc.e12-05-0415] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Sec1/Munc18 family proteins are important components of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex-mediated membrane fusion processes. However, the molecular interactions and the mechanisms involved in Sec1p/Munc18 control and SNARE complex assembly are not well understood. We provide evidence that Mso1p, a Sec1p- and Sec4p-binding protein, interacts with membranes to regulate membrane fusion. We identify two membrane-binding sites on Mso1p. The N-terminal region inserts into the lipid bilayer and appears to interact with the plasma membrane, whereas the C-terminal region of the protein binds phospholipids mainly through electrostatic interactions and may associate with secretory vesicles. The Mso1p membrane interactions are essential for correct subcellular localization of Mso1p-Sec1p complexes and for membrane fusion in Saccharomyces cerevisiae. These characteristics are conserved in the phosphotyrosine-binding (PTB) domain of β-amyloid precursor protein-binding Mint1, the mammalian homologue of Mso1p. Both Mint1 PTB domain and Mso1p induce vesicle aggregation/clustering in vitro, supporting a role in a membrane-associated process. The results identify Mso1p as a novel lipid-interacting protein in the SNARE complex assembly machinery. Furthermore, our data suggest that a general mode of interaction, consisting of a lipid-binding protein, a Rab family GTPase, and a Sec1/Munc18 family protein, is important in all SNARE-mediated membrane fusion events.
Collapse
Affiliation(s)
- Marion Weber-Boyvat
- Cell and Molecular Biology Program, Institute of Biotechnology, FI-00014 University of Helsinki, Helsinki, Finland
| | | | | | | | | | | | | | | |
Collapse
|
4
|
Weber-Boyvat M, Aro N, Chernov KG, Nyman T, Jäntti J. Sec1p and Mso1p C-terminal tails cooperate with the SNAREs and Sec4p in polarized exocytosis. Mol Biol Cell 2010; 22:230-44. [PMID: 21119007 PMCID: PMC3020918 DOI: 10.1091/mbc.e10-07-0592] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
It is shown that Sec1p C-terminal tail is needed for proper Sec1p-SNARE complex interaction. Furthermore, evidence is provided that the Mso1p C terminus collaborates with the GTP-bound form of Sec4p in the bud. These results reveal a role for the Sec1p C-terminal tail in SNARE complex binding and suggest Mso1p as an effector for Sec4p. The Sec1/Munc18 protein family members perform an essential, albeit poorly understood, function in association with soluble n-ethylmaleimide sensitive factor adaptor protein receptor (SNARE) complexes in membrane fusion. The Saccharomyces cerevisiae Sec1p has a C-terminal tail that is missing in its mammalian homologues. Here we show that deletion of the Sec1p tail (amino acids 658–724) renders cells temperature sensitive for growth, reduces sporulation efficiency, causes a secretion defect, and abolishes Sec1p-SNARE component coimmunoprecipitation. The results show that the Sec1p tail binds preferentially ternary Sso1p-Sec9p-Snc2p complexes and it enhances ternary SNARE complex formation in vitro. The bimolecular fluorescence complementation (BiFC) assay results suggest that, in the SNARE-deficient sso2–1 Δsso1 cells, Mso1p, a Sec1p binding protein, helps to target Sec1p(1–657) lacking the C-terminal tail to the sites of secretion. The results suggest that the Mso1p C terminus is important for Sec1p(1–657) targeting. We show that, in addition to Sec1p, Mso1p can bind the Rab-GTPase Sec4p in vitro. The BiFC results suggest that Mso1p acts in close association with Sec4p on intracellular membranes in the bud. This association depends on the Sec4p guanine nucleotide exchange factor Sec2p. Our results reveal a novel binding mode between the Sec1p C-terminal tail and the SNARE complex, and suggest a role for Mso1p as an effector of Sec4p.
Collapse
Affiliation(s)
- Marion Weber-Boyvat
- Cell and Molecular Biology Program Research Program in Structural Biology and Biophysics, Institute of Biotechnology, FI-0001 University of Helsinki, Finland
| | | | | | | | | |
Collapse
|
5
|
Weber M, Chernov K, Turakainen H, Wohlfahrt G, Pajunen M, Savilahti H, Jäntti J. Mso1p regulates membrane fusion through interactions with the putative N-peptide-binding area in Sec1p domain 1. Mol Biol Cell 2010; 21:1362-74. [PMID: 20181830 PMCID: PMC2854094 DOI: 10.1091/mbc.e09-07-0546] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
We show that the putative N-peptide binding area in Sec1p domain 1 is important for Mso1p binding and that Mso1p can interact with Sso1p and Sso2p. Our results suggest that Mso1p mimics N-peptide binding to facilitate membrane fusion. Sec1p/Munc18 (SM) family proteins regulate SNARE complex function in membrane fusion through their interactions with syntaxins. In addition to syntaxins, only a few SM protein interacting proteins are known and typically, their binding modes with SM proteins are poorly characterized. We previously identified Mso1p as a Sec1p-binding protein and showed that it is involved in membrane fusion regulation. Here we demonstrate that Mso1p and Sec1p interact at sites of exocytosis and that the Mso1p–Sec1p interaction site depends on a functional Rab GTPase Sec4p and its GEF Sec2p. Random and targeted mutagenesis of Sec1p, followed by analysis of protein interactions, indicates that Mso1p interacts with Sec1p domain 1 and that this interaction is important for membrane fusion. In many SM family proteins, domain 1 binds to a N-terminal peptide of a syntaxin family protein. The Sec1p-interacting syntaxins Sso1p and Sso2p lack the N-terminal peptide. We show that the putative N-peptide binding area in Sec1p domain 1 is important for Mso1p binding, and that Mso1p can interact with Sso1p and Sso2p. Our results suggest that Mso1p mimics N-peptide binding to facilitate membrane fusion.
Collapse
Affiliation(s)
- Marion Weber
- Research Program in Cell and Molecular Biology, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
| | | | | | | | | | | | | |
Collapse
|
6
|
Yang HJ, Neiman AM. A guaninine nucleotide exchange factor is a component of the meiotic spindle pole body in Schizosaccharomyces pombe. Mol Biol Cell 2010; 21:1272-81. [PMID: 20130084 PMCID: PMC2847530 DOI: 10.1091/mbc.e09-10-0842] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Spore morphogenesis in yeast is driven by the formation of membrane compartments that initiate growth at the spindle poles during meiosis II and grow to encapsulate daughter nuclei. Vesicle docking complexes, called meiosis II outer plaques (MOPs), form on each meiosis II spindle pole body (SPB) and serve as sites of membrane nucleation. How the MOP stimulates membrane assembly is not known. Here, we report that SpSpo13, a component of the MOP in Schizosaccharomyces pombe, shares homology with the guanine nucleotide exchange factor (GEF) domain of the Saccharomyces cerevisiae Sec2 protein. ScSec2 acts as a GEF for the small Rab GTPase ScSec4, which regulates vesicle trafficking from the late-Golgi to the plasma membrane. A chimeric protein in which the ScSec2-GEF domain is replaced with SpSpo13 is capable of supporting the growth of a sec2Delta mutant. SpSpo13 binds preferentially to the nucleotide-free form of ScSec4 and facilitates nucleotide exchange in vitro. In vivo, a Spspo13 mutant defective in GEF activity fails to support membrane assembly. In vitro specificity experiments suggest that SpYpt2 is the physiological substrate of SpSpo13. These results demonstrate that stimulation of Rab-GTPase activity is a property of the S. pombe MOP essential for the initiation of membrane formation.
Collapse
Affiliation(s)
- Hui-Ju Yang
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215, USA
| | | |
Collapse
|
7
|
Castillo-Flores A, Weinberger A, Robinson M, Gerst JE. Mso1 Is a Novel Component of the Yeast Exocytic SNARE Complex. J Biol Chem 2005; 280:34033-41. [PMID: 16087665 DOI: 10.1074/jbc.m507142200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The yeast exocytic SNARE complex consists of one molecule each of the Sso1/2 target SNAREs, Snc1/2 vesicular SNAREs, and the Sec9 target SNARE, which form a fusion complex that is conserved in evolution. Another protein, Sec1, binds to the SNARE complex to facilitate assembly. We show that Mso1, a Sec1-interacting protein, also binds to the SNARE complex and plays a role in mediating Sec1 functions. Like Sec1, Mso1 bound to SNAREs in cells containing SNARE complexes (i.e. wild-type, sec1-1, and sec18-1 cells), but not in cells in which complex formation is inhibited (i.e. sec4-8 cells). Nevertheless, Mso1 remained associated with Sec1 even in sec4-8 cells, indicating that they act as a pair. Mso1 localized primarily to the plasma membrane of the bud when SNARE complex formation was not impaired but was mostly in the cytoplasm when assembly was prevented. Genetic studies suggest that Mso1 enhances Sec1 function while attenuating Sec4 GTPase function. This dual action may impart temporal regulation between Sec4 turnoff and Sec1-mediated SNARE assembly. Notably, a small region at the C terminus of Mso1 is conserved in the mammalian Munc13/Mint proteins and is necessary for proper membrane localization. Overexpression of Mso1 lacking this domain (Mso1-(1-193)) inhibited the growth of cells bearing an attenuated Sec4 GTPase. These results suggest that Mso1 is a component of the exocytic SNARE complex and a possible ortholog of the Munc13/Mint proteins.
Collapse
|
8
|
Knop M, Miller KJ, Mazza M, Feng D, Weber M, Keränen S, Jäntti J. Molecular interactions position Mso1p, a novel PTB domain homologue, in the interface of the exocyst complex and the exocytic SNARE machinery in yeast. Mol Biol Cell 2005; 16:4543-56. [PMID: 16030256 PMCID: PMC1237063 DOI: 10.1091/mbc.e05-03-0243] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In this study, we have analyzed the association of the Sec1p interacting protein Mso1p with the membrane fusion machinery in yeast. We show that Mso1p is essential for vesicle fusion during prospore membrane formation. Green fluorescent protein-tagged Mso1p localizes to the sites of exocytosis and at the site of prospore membrane formation. In vivo and in vitro experiments identified a short amino-terminal sequence in Mso1p that mediates its interaction with Sec1p and is needed for vesicle fusion. A point mutation, T47A, within the Sec1p-binding domain abolishes Mso1p functionality in vivo, and mso1T47A mutant cells display specific genetic interactions with sec1 mutants. Mso1p coimmunoprecipitates with Sec1p, Sso1/2p, Snc1/2p, Sec9p, and the exocyst complex subunit Sec15p. In sec4-8 and SEC4I133 mutant cells, association of Mso1p with Sso1/2p, Snc1/2p, and Sec9p is affected, whereas interaction with Sec1p persists. Furthermore, in SEC4I133 cells the dominant negative Sec4I133p coimmunoprecipitates with Mso1p-Sec1p complex. Finally, we identify Mso1p as a homologue of the PTB binding domain of the mammalian Sec1p binding Mint proteins. These results position Mso1p in the interface of the exocyst complex, Sec4p, and the SNARE machinery, and reveal a novel layer of molecular conservation in the exocytosis machinery.
Collapse
|
9
|
Poussu E, Jäntti J, Savilahti H. A gene truncation strategy generating N- and C-terminal deletion variants of proteins for functional studies: mapping of the Sec1p binding domain in yeast Mso1p by a Mu in vitro transposition-based approach. Nucleic Acids Res 2005; 33:e104. [PMID: 16006618 PMCID: PMC1174911 DOI: 10.1093/nar/gni102] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Bacteriophage Mu in vitro transposition constitutes a versatile tool in molecular biology, with applications ranging from engineering of single genes or proteins to modification of genome segments or entire genomes. A new strategy was devised on the basis of Mu transposition that via a few manipulation steps simultaneously generates a nested set of gene constructions encoding deletion variants of proteins. C-terminal deletions are produced using a mini-Mu transposon that carries translation stop signals close to each transposon end. Similarly, N-terminal deletions are generated using a transposon with appropriate restriction sites, which allows deletion of the 5'-distal part of the gene. As a proof of principle, we produced a set of plasmid constructions encoding both C- and N-terminally truncated variants of yeast Mso1p and mapped its Sec1p-interacting region. The most important amino acids for the interaction in Mso1p are located between residues T46 and N78, with some weaker interactions possibly within the region E79-N105. This general-purpose gene truncation strategy is highly efficient and produces, in a single reaction series, a comprehensive repertoire of gene constructions encoding protein deletion variants, valuable in many types of functional studies. Importantly, the methodology is applicable to any protein-encoding gene cloned in an appropriate vector.
Collapse
Affiliation(s)
| | - Jussi Jäntti
- VTT BiotechnologyPO Box 1500, FI-02044, VTT, Finland
| | - Harri Savilahti
- To whom correspondence should be addressed. Tel: +358 9 19159516; Fax: +358 9 19159366.
| |
Collapse
|
10
|
|
11
|
Oyen M, Jäntti J, Keränen S, Ronne H. Mapping of sporulation-specific functions in the yeast syntaxin gene SSO1. Curr Genet 2003; 45:76-82. [PMID: 14652692 DOI: 10.1007/s00294-003-0462-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2003] [Revised: 10/19/2003] [Accepted: 10/19/2003] [Indexed: 11/29/2022]
Abstract
The yeast Saccharomyces cerevisiae has two closely related plasma membrane syntaxins, Sso1p and Sso2p, which together provide an essential function in vegetative cells. However, Sso1p is also specifically needed during sporulation; and this function cannot be provided by Sso2p. We used fusions between SSO1 and SSO2 to map the sporulation-specific function of SSO1. We found that the two N-terminal alpha-helices Ha and Hb of Sso1p are important for sporulation, since it is reduced 8-fold for fusions where Ha and Hb are derived from Sso2p. In contrast, the C-terminal half of Sso1p does not seem to be specifically required for sporulation. Surprisingly, we further found that the 3' untranslated region (3'UTR) of SSO1 is essential for sporulation. Western blots failed to reveal a preferential expression of Sso1p in sporulating cells, indicating that effects on gene expression are unlikely to explain why the SSO1 3'UTR is needed for sporulation.
Collapse
Affiliation(s)
- Mattias Oyen
- Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences, Box 7080, 75007 Uppsala, Sweden
| | | | | | | |
Collapse
|
12
|
Abstract
Most cells contain a variety of transport vesicles traveling to different destinations. Although many specific transport routes exist, the underlying molecular principles appear to be rather similar and conserved in evolution. It has become evident that formation of protein complexes named SNARE complexes between vesicle and target membrane is a central aspect of the final fusion reaction in many, if not all, routes and that SNARE complexes in different routes and species form in a similar manner. It is also evident that a second gene family, the Sec1/Munc18 genes (SM genes), plays a prominent role in vesicle trafficking. But, in contrast to the consensus and clarity about SNARE proteins, recent data on SM proteins in different systems produce an uncomfortable heterogeneity of ideas about their exact role, their site of action and their relation to SNARE proteins. This review examines whether a universal principle for the molecular function of SM genes exists and whether the divergence in SM gene function can be related to the unique characteristics of different transport routes.
Collapse
Affiliation(s)
- Ruud F G Toonen
- Department of Functional Genomics, Center for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam (VUA), De Boelelaan 1087, The Netherlands
| | | |
Collapse
|
13
|
Taxis C, Vogel F, Wolf DH. ER-golgi traffic is a prerequisite for efficient ER degradation. Mol Biol Cell 2002; 13:1806-18. [PMID: 12058050 PMCID: PMC117605 DOI: 10.1091/mbc.01-08-0399] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2001] [Revised: 02/19/2002] [Accepted: 02/22/2002] [Indexed: 11/11/2022] Open
Abstract
Protein quality control is an essential function of the endoplasmic reticulum. Misfolded proteins unable to acquire their native conformation are retained in the endoplasmic reticulum, retro-translocated back into the cytosol, and degraded via the ubiquitin-proteasome system. We show that efficient degradation of soluble malfolded proteins in yeast requires a fully competent early secretory pathway. Mutations in proteins essential for ER-Golgi protein traffic severely inhibit ER degradation of the model substrate CPY*. We found ER localization of CPY* in WT cells, but no other specific organelle for ER degradation could be identified by electron microscopy studies. Because CPY* is degraded in COPI coat mutants, only a minor fraction of CPY* or of a proteinaceous factor required for degradation seems to enter the recycling pathway between ER and Golgi. Therefore, we propose that the disorganized structure of the ER and/or the mislocalization of Kar2p, observed in early secretory mutants, is responsible for the reduction in CPY* degradation. Further, we observed that mutations in proteins directly involved in degradation of malfolded proteins (Der1p, Der3/Hrd1p, and Hrd3p) lead to morphological changes of the endoplasmic reticulum and the Golgi, escape of CPY* into the secretory pathway and a slower maturation rate of wild-type CPY.
Collapse
Affiliation(s)
- Christof Taxis
- Institut für Biochemie, Universität Stuttgart, 70569 Stuttgart, Germany
| | | | | |
Collapse
|
14
|
Thelander M, Fredriksson D, Schouten J, Hoge JHC, Ronne H. Cloning by pathway activation in yeast: identification of an Arabidopsis thaliana F-box protein that can turn on glucose repression. PLANT MOLECULAR BIOLOGY 2002; 49:69-79. [PMID: 12008900 DOI: 10.1023/a:1014440531842] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We describe a method for identifying signal transducing proteins from other organisms by their ability to turn on a signalling pathway when they are expressed at high level in yeast. The method was tested on a cDNA library from Arabidopsis thaliana, which was screened for clones that can activate glucose repression in the absence of glucose. Six clones were characterized. One of them codes for AtGRH1, a new F-box protein that shows similarity to GRR1, a yeast protein involved in glucose repression. The ability of AtGRHI to activate glucose repression is dependent on the MIG1 repressor. Two-hybrid experiments revealed that AtGRH1 can interact with AtSKP1a and AtSKP1b, two recently identified SKP1 homologues in Arabidopsis. Other clones identified in the screen encode the transcription factor AtEBP, the 14-3-3 protein AtGF14 and two new proteins: AtMYR1 and AtPOZ1. None of these proteins turn on glucose repression. Instead, they illustrate various other ways by which foreign proteins can interfere with expression of a yeast gene. We conclude that our method worked as expected in at least one case, and that it could be applied to other signalling pathways that are conserved between yeast and higher eukaryotes.
Collapse
Affiliation(s)
- Mattias Thelander
- Department of Plant Biology, Swedish University of Agricultural Sciences, Uppsala
| | | | | | | | | |
Collapse
|
15
|
Briza P, Bogengruber E, Thür A, Rützler M, Münsterkötter M, Dawes IW, Breitenbach M. Systematic analysis of sporulation phenotypes in 624 non-lethal homozygous deletion strains of Saccharomyces cerevisiae. Yeast 2002; 19:403-22. [PMID: 11921089 DOI: 10.1002/yea.843] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A new high throughput mutant screening procedure for the detection of sporulation mutants was developed and used to analyse a set of 624 non-lethal homozygous deletion mutants created in the European joint research program EUROFAN. The screening procedure involved determination of LL- and DL-dityrosine, sporulation-specific compounds, which were shown to be robust markers of the extent and arrest stage of sporulation mutants. Secondary screens consisted of light microscopy to detect mature and immature spores and DAPI staining to monitor the progress of meiotic nuclear divisions. We discovered new phenotypic classes of mutants defective in spore wall synthesis that were not discovered by previous screens for sporulation mutants. The genes corresponding to the sporulation mutants fell in several functional classes, some of which were previously unknown to be involved in spore formation. Peroxisomes seem to play a role in spore wall synthesis. Mitochondria play a role in sporulation that is not simply restricted to supply of ATP from respiratory metabolism. The deletion mutants included in the set were functionally unknown at the start of EUROFAN; however, within the last few years the importance to sporulation of some of them was also reported by other authors. Taken together, about 8% of all single gene deletion mutants of non-essential genes of Saccharomyces cerevisiae seem to display a clear and reproducible sporulation phenotype.
Collapse
Affiliation(s)
- Peter Briza
- Institut für Genetik und Allgemeine Biologie, Universität Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria
| | | | | | | | | | | | | |
Collapse
|
16
|
Jäntti J, Aalto MK, Oyen M, Sundqvist L, Keränen S, Ronne H. Characterization of temperature-sensitive mutations in the yeast syntaxin 1 homologues Sso1p and Sso2p, and evidence of a distinct function for Sso1p in sporulation. J Cell Sci 2002; 115:409-20. [PMID: 11839791 DOI: 10.1242/jcs.115.2.409] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The duplicated genes SSO1 and SSO2 encode yeast homologues of syntaxin 1 and perform an essential function during fusion of secretory vesicles at the plasma membrane. We have used in vitro mutagenesis to obtain a temperature-sensitive SSO2 allele, sso2-1, in which a conserved arginine has been changed to a lysine. A yeast strain that lacks SSO1 and carries the sso2-1 allele ceases growth and accumulates secretory vesicles at the restrictive temperature. Interestingly, the strain also has a pronounced phenotype at the permissive temperature, causing a defect in bud neck closure that prevents separation of mother and daughter cells. The same mutation was introduced into SSO1, producing the sso1-1 allele, which also has a temperature-sensitive phenotype, although less pronounced than sso2-1. A screen for high copy number suppressors of sso2-1 yielded three genes that are involved in the terminal step of secretion: SNC1, SNC2 and SEC9. The sso1-1 mutation interacts synthetically with a disruption of the MSO1 gene, which encodes a Sec1p interacting protein. Interestingly, we further found that both MSO1 and SSO1, but not SSO2, are required for sporulation. This difference is not due to differential expression, since SSO2 expressed from the SSO1 promoter failed to restore sporulation. We conclude that a functional difference exists between the Sso1 and Sso2 proteins, with the former being specifically required during sporulation.
Collapse
Affiliation(s)
- Jussi Jäntti
- VTT Biotechnology, PO Box 1500, FIN-02044 VTT, Finland
| | | | | | | | | | | |
Collapse
|
17
|
Brummer MH, Kivinen KJ, Jäntti J, Toikkanen J, Söderlund H, Keränen S. Characterization of the sec1-1 and sec1-11 mutations. Yeast 2001; 18:1525-36. [PMID: 11748729 DOI: 10.1002/yea.796] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Sec1 proteins are implicated in positive and negative regulation of SNARE complex formation. To better understand the function of Sec1 proteins we have identified the nature of the temperature-sensitive mutations in sec1-1 and sec1-11. The sec1-1 mutation changes a conserved glycine(443) to glutamic acid. The sec1-11 mutation changes a highly conserved arginine(432) to proline. Based on homology and the crystal structure of the mammalian nSec1p, the corresponding amino acids localize to the 3b domain of nSec1p. Compared to the wild-type Sec1p the mutant proteins are less abundant even at the permissive temperature. Thus, the R432P and G443E mutations may cause structural alterations that affect folding and make the mutant proteins more susceptible to degradation. The remaining part is sufficient for growth and protein secretion at 24 degrees C and thus is likely to be properly folded. At 37 degrees C the mutant proteins become non-functional. In pulse-chase-type experiments the newly synthesized Sec1-1 and Sec1-11 proteins decayed similarly with the wild-type protein. Thus, the non-functionality of the mutant proteins cannot be explained by denaturation-induced degradation only. It is possible that the newly synthesized mutant proteins fold slowly and are susceptible to degradation before they have managed to fold and associate with other proteins. The mutant proteins were unable to interact with the Sec1p-interacting proteins Mso1p and Sso2p in the two-hybrid assay, even at the permissive temperature. These results localize sec1-1 and sec1-11 mutations to a domain of Sec1p and suggest a mechanism by which sec1-1 and sec1-11 cells become temperature-sensitive.
Collapse
Affiliation(s)
- M H Brummer
- VTT Biotechnology, PO Box 1500, FIN-02044 VTT Espoo, Finland
| | | | | | | | | | | |
Collapse
|
18
|
Murén E, Oyen M, Barmark G, Ronne H. Identification of yeast deletion strains that are hypersensitive to brefeldin A or monensin, two drugs that affect intracellular transport. Yeast 2001; 18:163-72. [PMID: 11169758 DOI: 10.1002/1097-0061(20010130)18:2<163::aid-yea659>3.0.co;2-#] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We have screened the Eurofan deletion strain collection for mutants that are either sensitive or resistant to three drugs known to affect intracellular transport: brefeldin A, monensin and C(2)-ceramide. Drug-sensitive mutants were analysed by complementation with cognate clones and tetrad analysis to confirm that the phenotypes are linked to the deletions. Out of 620 deletion strains, we found 18 mutants that were sensitive to either brefeldin A, monensin or both. Several of these mutants are deleted for genes that are known to be involved in intracellular transport, membrane biogenesis and/or cell wall biosynthesis. Among such previously known genes were VAM6, VAC7, SYS1, TLG2, RCY1, ERG4, ALG9 and ALG12. Some other genes recovered in our screen were not previously implicated in intracellular transport, but are related to other yeast genes with such a function. Still other genes encode proteins with no obvious link to intracellular transport. Several of these are putative transcription factors or RNA-binding proteins, which suggests that they may affect drug sensitivity by modulating the expression of other genes or proteins.
Collapse
Affiliation(s)
- E Murén
- Department of Plant Biology, Uppsala Genetic Center, Swedish University of Agricultural Sciences, Box 7080, S-750 07 Uppsala, Sweden
| | | | | | | |
Collapse
|
19
|
Katz L, Brennwald P. Testing the 3Q:1R "rule": mutational analysis of the ionic "zero" layer in the yeast exocytic SNARE complex reveals no requirement for arginine. Mol Biol Cell 2000; 11:3849-58. [PMID: 11071911 PMCID: PMC15041 DOI: 10.1091/mbc.11.11.3849] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The crystal structure of the synaptic SNARE complex reveals a parallel four-helix coiled-coil arrangement; buried in the hydrophobic core of the complex is an unusual ionic layer composed of three glutamines and one arginine, each provided by a separate alpha-helix. The presence of glutamine or arginine residues in this position is highly conserved across the t- and v-SNARE families, and it was recently suggested that a 3Q:1R ratio is likely to be a general feature common to all SNARE complexes. In this study, we have used genetic and biochemical assays to test this prediction with the yeast exocytic SNARE complex. We have determined that the relative position of Qs and Rs within the layer is not critical for biological activity and that Q-to-R substitutions in the layer reduce complex stability and result in lethal or conditional lethal growth defects. Surprisingly, SNARE complexes composed of four glutamines are fully functional for assembly in vitro and exocytic function in vivo. We conclude that the 3Q:1R layer composition is not required within the yeast exocytic SNARE complex because complexes containing four Q residues in the ionic layer appear by all criteria to be functionally equivalent. The unexpected flexibility of this layer suggests that there is no strict requirement for the 3Q:1R combination and that the SNARE complexes at other stages of transport may be composed entirely of Q-SNAREs or other noncanonical combinations.
Collapse
Affiliation(s)
- L Katz
- Department of Cell Biology and Graduate Program in Cell Biology and Genetics, Weill Medical College of Cornell University, New York, New York 10021, USA
| | | |
Collapse
|
20
|
Legesse-Miller A, Sagiv Y, Glozman R, Elazar Z. Aut7p, a soluble autophagic factor, participates in multiple membrane trafficking processes. J Biol Chem 2000; 275:32966-73. [PMID: 10837468 DOI: 10.1074/jbc.m000917200] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Aut7p, a protein recently implicated in autophagic events in the yeast Saccharomyces cerevisiae, exhibits significant homology to a mammalian protein, p16, herein termed GATE-16 (Golgi-associated ATPase Enhancer of 16 kDa), a novel intra-Golgi transport factor. Here we provide evidence for the involvement of Aut7p in different membrane trafficking processes. Aut7p largely substitutes for the activity of GATE-16 in mammalian intra-Golgi transport in vitro. In vivo, AUT7 interacts genetically with endoplasmic reticulum to Golgi SNAREs, specifically with BET1 and SEC22. Aut7p interacts physically with the following two v-SNAREs: Bet1p, which is involved in endoplasmic reticulum to Golgi vesicular transport, and Nyv1p, implicated in vacuolar inheritance. We suggest that, in addition to its role in autophagocytosis, Aut7p has pleiotropic effects and participates in at least two membrane traffic events.
Collapse
Affiliation(s)
- A Legesse-Miller
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, 76100 Israel
| | | | | | | |
Collapse
|
21
|
Bracher A, Perrakis A, Dresbach T, Betz H, Weissenhorn W. The X-ray crystal structure of neuronal Sec1 from squid sheds new light on the role of this protein in exocytosis. Structure 2000; 8:685-94. [PMID: 10903948 DOI: 10.1016/s0969-2126(00)00156-8] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
BACKGROUND Sec1-like molecules have been implicated in a variety of eukaryotic vesicle transport processes including neurotransmitter release by exocytosis. They regulate vesicle transport by binding to a t-SNARE from the syntaxin family. This process is thought to prevent SNARE complex formation, a protein complex required for membrane fusion. Whereas Sec1 molecules are essential for neurotransmitter release and other secretory events, their interaction with syntaxin molecules seems to represent a negative regulatory step in secretion. RESULTS Here we report the X-ray crystal structure of a neuronal Sec1 homologue from squid, s-Sec1, at 2.4 A resolution. Neuronal s-Sec1 is a modular protein that folds into a V-shaped three-domain assembly. Peptide and mutagenesis studies are discussed with respect to the mechanism of Sec1 regulation. Comparison of the structure of squid s-Sec1 with the previously determined structure of rat neuronal Sec1 (n-Sec1) bound to syntaxin-1a indicates conformational rearrangements in domain III induced by syntaxin binding. CONCLUSIONS The crystal structure of s-Sec1 provides the molecular scaffold for a number of molecular interactions that have been reported to affect Sec1 function. The structural differences observed between s-Sec1 and the structure of a rat n-Sec1-syntaxin-1a complex suggest that local conformational changes are sufficient to release syntaxin-1a from neuronal Sec1, an active process that is thought to involve additional effector molecule(s).
Collapse
Affiliation(s)
- A Bracher
- European Molecular Biology Laboratory (EMBL), Grenoble, 38000, France
| | | | | | | | | |
Collapse
|
22
|
Abstract
Membrane fusion involves the merger of two phospholipid bilayers in an aqueous environment. In artificial lipid bilayers, fusion proceeds by means of defined transition states, including hourglass-shaped intermediates in which the proximal leaflets of the fusing membranes are merged whereas the distal leaflets are separate (fusion stalk), followed by the reversible opening of small aqueous fusion pores. Fusion of biological membranes requires the action of specific fusion proteins. Best understood are the viral fusion proteins that are responsible for merging the viral with the host cell membrane during infection. These proteins undergo spontaneous and dramatic conformational changes upon activation. In the case of the paradigmatic fusion proteins of the influenza virus and of the human immunodeficiency virus, an amphiphilic fusion peptide is inserted into the target membrane. The protein then reorients itself, thus forcing the fusing membranes together and inducing lipid mixing. Fusion of intracellular membranes in eukaryotic cells involves several protein families including SNAREs, Rab proteins, and Sec1/Munc-18 related proteins (SM-proteins). SNAREs form a novel superfamily of small and mostly membrane-anchored proteins that share a common motif of about 60 amino acids (SNARE motif). SNAREs reversibly assemble into tightly packed helical bundles, the core complexes. Assembly is thought to pull the fusing membranes closely together, thus inducing fusion. SM-proteins comprise a family of soluble proteins that bind to certain types of SNAREs and prevent the formation of core complexes. Rab proteins are GTPases that undergo highly regulated GTP-GDP cycles. In their GTP form, they interact with specific proteins, the effector proteins. Recent evidence suggests that Rab proteins function in the initial membrane contact connecting the fusing membranes but are not involved in the fusion reaction itself.
Collapse
Affiliation(s)
- R Jahn
- Department of Neurobiology, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
| | | |
Collapse
|
23
|
Gupta GD, Heath IB. A tip-high gradient of a putative plasma membrane SNARE approximates the exocytotic gradient in hyphal apices of the fungus Neurospora crassa. Fungal Genet Biol 2000; 29:187-99. [PMID: 10882535 DOI: 10.1006/fgbi.2000.1200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Antibodies to the Saccharomyces cereviseae plasma membrane t-SNARE Sso2p identify a putative 39-kDa homologue in Neurospora crassa. The 39-kDa protein is enriched in plasma membrane (PM) and occurred with other membranes. It is extractable by detergent, but not chaotropic or alkali agents, suggesting membrane insertion. Immunoprecipitation with anti-Sso2p coprecipitated a approximately 100-kDa, Mg(+)-ATP-sensitive band with the 39-kDa protein, suggesting a ternary SNARE complex. Affinity-purified anti-Sso2p gave hyphal staining patterns most consistent with protein localization on both the PM and intracellular exocytotic apical wall vesicles. The PM staining in hyphal apices formed a tip-high gradient, not as steep as that predicted by the "hyphoid equation," but closer to published gradients of cell wall matrix deposition. We conclude that the t-SNAREs are transported to the PM on the apical vesicles, but their tip-high gradient alone is insufficient to explain the vesicle fusion gradient in growing tips.
Collapse
Affiliation(s)
- G D Gupta
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, M3J 1P3, Canada
| | | |
Collapse
|
24
|
Abstract
This article describes genetic approaches to the study of heterologous protein-protein interactions, focusing on the yeast Saccharomyces cerevisiae as a useful eukaryotic model system. Several methods are described that can be used to search for new interactions, including extragenic suppression, multicopy suppression, synthetic lethality, and transdominant inhibition. Strategies for screening, genetic characterization, and clone identification are described, along with recent examples from the literature. In addition, genetic methods are discussed that can be used to further characterize a newly discovered protein-protein interaction. These include the creation of mutant libraries of a given protein by chemical mutagenesis or polymerase chain reaction, the production of dominant-negative mutants, and strategies for introducing these mutant alleles back into yeast for analysis. Although these genetic methods are quite powerful, they are often just a starting point for further biochemical or cell biological experiments.
Collapse
Affiliation(s)
- D R Appling
- Department of Chemistry and Biochemistry, The Biochemical Institute, Austin, Texas 78712, USA.
| |
Collapse
|
25
|
Carr CM, Grote E, Munson M, Hughson FM, Novick PJ. Sec1p binds to SNARE complexes and concentrates at sites of secretion. J Cell Biol 1999; 146:333-44. [PMID: 10427089 PMCID: PMC3206579 DOI: 10.1083/jcb.146.2.333] [Citation(s) in RCA: 258] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/1999] [Accepted: 06/22/1999] [Indexed: 11/22/2022] Open
Abstract
Proteins of the Sec1 family have been shown to interact with target-membrane t-SNAREs that are homologous to the neuronal protein syntaxin. We demonstrate that yeast Sec1p coprecipitates not only the syntaxin homologue Ssop, but also the other two exocytic SNAREs (Sec9p and Sncp) in amounts and in proportions characteristic of SNARE complexes in yeast lysates. The interaction between Sec1p and Ssop is limited by the abundance of SNARE complexes present in sec mutants that are defective in either SNARE complex assembly or disassembly. Furthermore, the localization of green fluorescent protein (GFP)-tagged Sec1p coincides with sites of vesicle docking and fusion where SNARE complexes are believed to assemble and function. The proposal that SNARE complexes act as receptors for Sec1p is supported by the mislocalization of GFP-Sec1p in a mutant defective for SNARE complex assembly and by the robust localization of GFP-Sec1p in a mutant that fails to disassemble SNARE complexes. The results presented here place yeast Sec1p at the core of the exocytic fusion machinery, bound to SNARE complexes and localized to sites of secretion.
Collapse
Affiliation(s)
- Chavela M. Carr
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510
| | - Eric Grote
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510
| | - Mary Munson
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544
| | - Frederick M. Hughson
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544
| | - Peter J. Novick
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510
| |
Collapse
|
26
|
Jäntti J, Lahdenranta J, Olkkonen VM, Söderlund H, Keränen S. SEM1, a homologue of the split hand/split foot malformation candidate gene Dss1, regulates exocytosis and pseudohyphal differentiation in yeast. Proc Natl Acad Sci U S A 1999; 96:909-14. [PMID: 9927667 PMCID: PMC15324 DOI: 10.1073/pnas.96.3.909] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The exocyst is an essential multiprotein complex mediating polarized secretion in yeast. Here we describe a gene, SEM1, that can multicopy-suppress exocyst mutants sec3-2, sec8-9, sec10-2, and sec15-1. SEM1 is highly conserved among eukaryotic species. Its human homologue, DSS1, has been suggested as a candidate gene for the split hand/split foot malformation disorder. SEM1 is not an essential gene. However, its deletion rescued growth of the temperature-sensitive exocyst mutants sec3-2, sec8-9, sec10-1, and sec15-1 at the restrictive temperature. Cell fractionation showed that Sem1p is mainly cytosolic but also associates with the microsomal fraction. In linear sucrose gradients, Sem1p cosedimented with the exocyst component Sec8p. In diploid cells that normally do not form pseudohyphae (S288C background), deletion of SEM1 triggered pseudohyphal growth. This phenotype was abolished after reintroduction of either SEM1 or the mouse homologue Dss1 into the cells. In diploids that have normal capacity for pseudohyphal growth (Sigma1278b background), deletion of SEM1 enhanced filamentous growth. The functionality of both SEM1 and Dss1 in a differentiation process in yeast suggests that Dss1 indeed could be the gene affected in the split hand/split foot malformation disorder. These results characterize SEM1 as a regulator of both exocyst function and pseudohyphal differentiation and suggest a unique link between these two cellular functions in yeast.
Collapse
Affiliation(s)
- J Jäntti
- VTT Biotechnology and Food Research, Biologinkuja 1, FIN-02044 VTT Espoo, Finland
| | | | | | | | | |
Collapse
|
27
|
Riento K, Galli T, Jansson S, Ehnholm C, Lehtonen E, Olkkonen VM. Interaction of Munc-18-2 with syntaxin 3 controls the association of apical SNAREs in epithelial cells. J Cell Sci 1998; 111 ( Pt 17):2681-8. [PMID: 9701566 DOI: 10.1242/jcs.111.17.2681] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The docking/fusion of transport vesicles mediated by the soluble NSF attachment protein receptors (SNAREs) is thought to be regulated by Sec1-related proteins. Munc-18-2, a member of this family, is predominantly expressed in the epithelial cells of several tissues. We demonstrate here that Munc-18-2 colocalizes with syntaxin 3 at the apical plasma membrane of intestinal epithelium and Caco-2 cells. The presence of a physical complex of the two proteins is verified by 2-way coimmunoprecipitation. The quantity of the complex is reduced by treatment of Caco-2 cells with the alkylating agent N-ethylmaleimide which also has an inhibitory effect on the ability of Munc-18-2 to associate with syntaxin 3 in vitro. The amount of Munc-18-2 in the complex increases upon treatment of the cells with the protein kinase C activator phorbol myristate acetate, indicating a functional connection between the complex and cell signalling. Increasing the amount of Munc-18-2 bound to syntaxin 3 by overexpression results in a marked decrease in the SNARE proteins SNAP-23 and cellubrevin bound to the syntaxin. These results define a novel functional complex of Munc-18-2 and syntaxin 3 involved in the regulation of apical membrane transport.
Collapse
Affiliation(s)
- K Riento
- Department of Biochemistry, National Public Health Institute, Mannerheimintie 166, FIN-00300, Helsinki, Finland
| | | | | | | | | | | |
Collapse
|