High impact information on SEC9

• Sec9 is a SNAP-25-like component of a yeast SNARE complex that may be the effector of Sec4 function in exocytosis [1].
• Analogous to SNAP-25, Sec9 is bound to the yeast plasma membrane and is absent from post-Golgi vesicles [1].
• Although there are numerous homologues of syntaxin on intracellular membranes, there are only two SNAP-25-related proteins in yeast, Sec9 and Spo20, both of which are localized to the plasma membrane and function in secretion and sporulation, respectively [2].
• Furthermore, we demonstrate the formation of a ternary complex of Sec4-GTP, Sro7p, and the t-SNARE Sec9p [3].
• Sso t-SNARE dephosphorylation correlated with its assembly into complexes with the Sec9 t-SNARE, both in vitro and in vivo, and with an increase in protein trafficking and secretion in cells [4].

Biological context of SEC9

• Yeast homologues of tomosyn and lethal giant larvae function in exocytosis and are associated with the plasma membrane SNARE, Sec9 [5].
• A similar phenotype was seen when the t-SNARE Sso1p, or the partially redundant t-SNAREs Sec9p and Spo20p were mutated [6].
• In summary, we report the finding that yeast Par-1 counterparts are associated with and regulate the function of the exocytic apparatus via phosphorylation of Sec9 [7].
• Dimerization of the exocyst protein Sec6p and its interaction with the t-SNARE Sec9p [8].

Anatomical context of SEC9

• We suggest, then, that recognition of the plasma membrane by secretory vesicles may involve the formation of a Snc-Sec9 complex and that this interaction has evolved as a fundamental step in secretory processes [9].

Associations of SEC9 with chemical compounds

• In yeast, assembly of exocytic soluble N-ethylmaleimide-sensitive fusion protein (NSF) attachment protein receptor (SNARE) complexes between the secretory vesicle SNARE Sncp and the plasma membrane SNAREs Ssop and Sec9p occurs at a late stage of the exocytic reaction [10].
• Using epitope tags, antibodies and maltose-binding protein markers, we find that the helical domains of Sso, Snc and both halves of Sec9 are all aligned in parallel within the SNARE complex, suggesting that the yeast exocytic SNARE complex consists of a parallel four helix bundle [11].

Physical interactions of SEC9

• A chimeric molecule, in which the helices of Sec9p that bind to Sso1/2p and Snc1/2p are replaced with the homologous regions of Spo20p, will not support vesicle fusion in vegetative cells [12].

Regulatory relationships of SEC9

• Finally, we find that Kin1 and Kin2 induce phosphorylation of t-SNARE Sec9 in vivo and stimulate its release from the plasma membrane [7].
• Furthermore, we provide genetic evidence to suggest that specific subunits of the yeast exocyst complex (i.e. a component of the plasma membrane vesicle docking machinery) and the Sec9p plasma membrane t-SNARE are regulated by PtdIns(4,5)P2 and that Sfh5p helps regulate this interface in vivo [13].

Other interactions of SEC9

• We show that similar to Sec9, Sro7/77 functions in the docking and fusion of post-Golgi vesicles with the plasma membrane [5].
• SEC9 and SPO20 encode SNARE proteins related to the mammalian SNAP-25 family [12].
• Genetic analysis suggests that Sro7 and Sec9 function together in a pathway downstream of the Rho3 GTPase [5].
• Sec9p associates with the SNAREs Sso1/2p and Snc1/2p to promote the fusion of vesicles with the plasma membrane [12].
• Our results identify Sec9 as the yeast cognate of SNAP-25 and suggest that SNARE complexes acting at specific stages of vesicular transport serve as the ultimate targets of regulation by members of the Sec4/Ypt1/Rab family of GTPases [1].

References