Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.26 (invertase)
 4,927 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The protein trafficking machinery of eukaryotic cells is employed for protein secretion and for the localization of resident proteins of the exocytic and endocytic pathways. Protein transit between organelles is mediated by transport vesicles that bear integral membrane proteins (v-SNAREs) which selectively interact with similar proteins on the target membrane (t-SNAREs), resulting in a docked vesicle. A novel Saccharomyces cerevisiae SNARE protein, which has been termed Vti1p, was identified by its sequence similarity to known SNAREs. Vti1p is a predominantly Golgi-localized 25-kDa type II integral membrane protein that is essential for yeast viability. Vti1p can bind Sec17p (yeast SNAP) and enter into a Sec18p (NSF)-sensitive complex with the cis-Golgi t-SNARE Sed5p. This Sed5p/Vti1p complex is distinct from the previously described Sed5p/Sec22p anterograde vesicle docking complex. Depletion of Vti1p in vivo causes a defect in the transport of the vacuolar protein carboxypeptidase Y through the Golgi. Temperature-sensitive mutants of Vti1p show a similar carboxypeptidase Y trafficking defect, but the secretion of invertase and gp400/hsp150 is not significantly affected. The temperature-sensitive vti1 growth defect can be rescued by the overexpression of the v-SNARE, Ykt6p, which physically interacts with Vti1p. We propose that Vti1p, along with Ykt6p and perhaps Sft1p, acts as a retrograde v-SNARE capable of interacting with the cis-Golgi t-SNARE Sed5p.
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PMID:Characterization of a novel yeast SNARE protein implicated in Golgi retrograde traffic. 939 83

SNAP receptor (SNARE) and Sec1/Munc18 (SM) proteins are required for all intracellular membrane fusion events. SNAREs are widely believed to drive the fusion process, but the function of SM proteins remains unclear. To shed light on this, we screened for dominant-negative mutants of yeast Sec1 by random mutagenesis of a GAL1-regulated SEC1 plasmid. Mutants were identified on the basis of galactose-inducible growth arrest and inhibition of invertase secretion. This effect of dominant-negative sec1 was suppressed by overexpression of the vesicle (v)-SNAREs, Snc1 and Snc2, but not the target (t)-SNAREs, Sec9 and Sso2. The mutations isolated in Sec1 clustered in a hotspot within domain 3a, with F361 mutated in four different mutants. To test if this region was generally involved in SM protein function, the F361-equivalent residue in mammalian Munc18-1 (Y337) was mutated. Overexpression of the Munc18-1 Y337L mutant in bovine chromaffin cells inhibited the release kinetics of individual exocytosis events. The Y337L mutation impaired binding of Munc18-1 to the neuronal SNARE complex, but did not affect its binary interaction with syntaxin1a. Taken together, these data suggest that domain 3a of SM proteins has a functionally important role in membrane fusion. Furthermore, this approach of screening for dominant-negative mutants in yeast may be useful for other conserved proteins, to identify functionally important domains in their mammalian homologs.
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PMID:A random mutagenesis approach to isolate dominant-negative yeast sec1 mutants reveals a functional role for domain 3a in yeast and mammalian Sec1/Munc18 proteins. 1875 20