Molecular Interactions Position Mso1p, a Novel PTB Domain Homologue, in the Interface of the Exocyst Complex and the Exocytic SNARE Machinery in Yeast

Knop, Michael; Miller, Karl Juha; Mazza, M.; Feng, Dejiang; Weber, Marion; Keränen, Sirkka; Jäntti, Jussi

doi:10.1091/mbc.e05-03-0243

Cited by 32 publications

(70 citation statements)

References 57 publications

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“…Moreover, binding experiments performed with locked forms of Sec4 (e.g. Sec4-N133I) showed that they could also coprecipitate with Mso1 and the SNARE complex (62). This lends support to the idea that Mso1 and Sec4 interact during SNARE assembly.…”

Section: Discussionsupporting

confidence: 54%

Mso1 Is a Novel Component of the Yeast Exocytic SNARE Complex

Castillo-Flores

Weinberger

Robinson

et al. 2005

Journal of Biological Chemistry

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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.The membrane fusion apparatus in eukaryotes relies upon SNAREs 2 to mediate intracellular membrane docking and fusion events. SNAREs are membrane-associated proteins bearing ␣-helical domains (termed SNARE motifs) that can assemble into intermolecular four-helix bundles (1-3). Assembly of the SNARE complex, which is composed of vesicular (v) and target (t) SNAREs (or R-and Q-SNAREs, depending upon the nomenclature followed), bridges apposed bilayers and allows for the extrusion of interposed water molecules, resulting in membrane fusion. Although shown to be sufficient to confer membrane fusion in vitro or under artificial conditions (4 -6), a number of other molecules (termed SNARE regulators) act upstream of the SNAREs and play essential roles in the temporal and spatial control of SNARE assembly in vivo (7-9). At the level of exocytosis, these include the Rab family of small GTPases; the vesicle-tethering exocyst complex; the Sec1/ Munc18 family of SNARE assembly factors, which are conserved from yeast to mammals; and the complexin, Mint, Munc13, and synaptotagmin families of SNARE regulators, which appear to act only upon stimulus-coupled exocytic processes (7-10).In yeast, the exocytic SNARE complex consists of one representative molecule each of the Sso1/2 t-SNAREs (Q-SNARE) (11) and Snc1/2 v-SNAREs (R-SNARE) (12) as well as one molecule of the Sec9 t-SNARE (Q-SNARE) (13). However, all Q-SNARE complexes composed either of a mutated Snc v-SNARE and one molecule each of Sso and Sec9 (14, 15) or of two molecules of Sso and one of Sec9 (16) have also been shown to be ...

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Section: Discussionsupporting

confidence: 54%

Mso1 Is a Novel Component of the Yeast Exocytic SNARE Complex

Castillo-Flores

Weinberger

Robinson

et al. 2005

Journal of Biological Chemistry

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“…Recent support for a homotypic vesicle fusion event came from the analysis of the ⌬mso1 mutant, which affects the function of Sec1 and SNARE complex formation in meiosis. In this case, unfused vesicles that are tightly docked to the meiotic plaque are visible (39). The comparison of this phenotype with the one in the ⌬spo14 mutant suggests that the vesicles at the SPBs appear to be much looser bound to the SPBs in the ⌬spo14 mutant.…”

Section: Discussionmentioning

confidence: 80%

“…It is thought that PSM formation is initiated by the fusion of vesicles at the SPB that generate an initial compartment, which then subsequently becomes enlarged and grows around the haploid nucleus to which it is connected via the SPB. Only recently support for this model came from the analysis of a ⌬mso1 mutant in which a block of PSM formation on the level of vesicle fusion at the SPB was visible (39).…”

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confidence: 99%

Differential Requirement for Phospholipase D/Spo14 and Its Novel Interactor Sma1 for Regulation of Exocytotic Vesicle Fusion in Yeast Meiosis

Riedel

Mazza

Maier

et al. 2005

Journal of Biological Chemistry

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During sporulation and meiosis of budding yeast a developmental program determines the formation of the new plasma membranes of the spores. This process of prospore membrane (PSM) formation leads to the formation of meiotic daughter cells, the spores, within the lumen of the mother cell. It is initiated at the spindle pole bodies during meiosis II. Spore formation, but not meiotic cell cycle progression, requires the function of phospholipase D (PLD/Spo14). Here we show that PLD/Spo14 forms a complex with Sma1, a meiotically expressed protein essential for spore formation. Detailed analysis revealed that both proteins are required for early steps of prospore membrane assembly but with distinct defects in the respective mutants. In the ⌬spo14 mutant the initiation of PSM formation is blocked and aggregated vesicles of homogenous size are detected at the spindle pole bodies. In contrast, initiation of PSM formation does occur in the ⌬sma1 mutant, but the enlargement of the membrane is impaired. During PSM growth both Spo14 and Sma1 localize to the membrane, and localization of Spo14 is independent of Sma1. Biochemical analysis revealed that Sma1 is not necessary for PLD activity per se and that PLD present in a complex with Sma1 is highly active. Together, our results suggest that yeast PLD is involved in two distinct but essential steps during the regulated vesicle fusion necessary for the assembly of the membranous encapsulations of the spores.During cellular differentiation and development, tightly controlled cell polarity changes occur (1). These changes involve redirection of the secretory pathway and specify the site of exocytosis. For these processes, molecular mechanisms exist that ensure correct delivery of membranes and secretory proteins in response to cellular signals. During yeast gametogenesis (sporulation) so-called prospore membranes (PSMs) 5 form de novo at sites adjacent to the spindle pole bodies (SPBs), the centrosomes of yeast (2). This process involves redirection of the secretory machinery to the SPB (3) and results in formation of four haploid cells within the mother cell. The initiation of this process is a tightly regulated event that occurs exactly once per SPB at the onset of meiosis II. It is thought that PSM formation is initiated by the fusion of vesicles at the SPB that generate an initial compartment, which then subsequently becomes enlarged and grows around the haploid nucleus to which it is connected via the SPB. Only recently support for this model came from the analysis of a ⌬mso1 mutant in which a block of PSM formation on the level of vesicle fusion at the SPB was visible (39).The formation of PSMs appears to require several genes known to act in the exocytosis of post-Golgi vesicles in vegetatively growing (mitotic) cells. In temperature-sensitive mutants of sec1, sec4, and sec8 or cells deleted for the syntaxin SSO1, no PSM formation occurs at the restrictive temperature (3, 4). In addition, PSM formation requires Spo20, a sporulation-specific Sec9 target SNARE homologue (3...

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“…In wild-type cells, vps13 mutants that had small prospore membranes (35), ady4 mutants that had abnormal prospore membranes (41), and ady3 mutants, the average SPBGolgi apparatus distances were essentially the same. By contrast, in three different mutants that formed very small or absent prospore membranes, sso1, mso1, or sma1 (22,34,44), the distance from the SPB to the Golgi apparatus was much greater. Therefore, a shorter SPB-Golgi apparatus distance correlates with the presence of a prospore membrane.…”

mentioning

confidence: 79%

Alternative Modes of Organellar Segregation during Sporulation in Saccharomyces cerevisiae

et al. 2007

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Formation of ascospores in the yeast Saccharomyces cerevisiae is driven by an unusual cell division in which daughter nuclei are encapsulated within de novo-formed plasma membranes, termed prospore membranes. Generation of viable spores requires that cytoplasmic organelles also be captured along with nuclei. In mitotic cells segregation of mitochondria into the bud requires a polarized actin cytoskeleton. In contrast, genes involved in actin-mediated transport are not essential for sporulation. Instead, efficient segregation of mitochondria into spores requires Ady3p, a component of a protein coat found at the leading edge of the prospore membrane. Other organelles whose mitotic segregation is promoted by actin, such as the vacuole and the cortical endoplasmic reticulum, are not actively segregated during sporulation but are regenerated within spores. These results reveal that organellar segregation into spores is achieved by mechanisms distinct from those in mitotic cells.

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Molecular Interactions Position Mso1p, a Novel PTB Domain Homologue, in the Interface of the Exocyst Complex and the Exocytic SNARE Machinery in Yeast

Cited by 32 publications

References 57 publications

Mso1 Is a Novel Component of the Yeast Exocytic SNARE Complex

Mso1 Is a Novel Component of the Yeast Exocytic SNARE Complex

Differential Requirement for Phospholipase D/Spo14 and Its Novel Interactor Sma1 for Regulation of Exocytotic Vesicle Fusion in Yeast Meiosis

Alternative Modes of Organellar Segregation during Sporulation in Saccharomyces cerevisiae

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