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Slp4-a/granuphilin-a interacts with syntaxin-2/3 in a Munc18-2-dependent manner
Mitsunori Fukuda1, Akane Imai, Tomoko Nashida
1Fukuda Initiative Research Unit, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. mnfukuda@brain.riken.go.jp
The Journal of Biological Chemistry
|September 28, 2005
Summary
Granuphilin-a (Slp4-a) interacts with syntaxin-2/3 and Munc18-2 in parotid acinar cells, modulating amylase release. This protein complex is crucial for regulating exocytosis in salivary glands.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Slp4-a (granuphilin-a) is known to associate with insulin granules in pancreatic beta-cells.
- Its role in amylase release from parotid acinar cells and its binding partners in this context were unknown.
- Parotid acinar cells lack syntaxin-1a and Munc18-1, suggesting different regulatory mechanisms for exocytosis.
Purpose of the Study:
- To investigate the binding partners of Slp4-a during amylase release in parotid acinar cells.
- To elucidate the molecular interactions governing Slp4-a's function in exocytosis of amylase-containing granules.
- To identify the specific syntaxin and Munc18 proteins interacting with Slp4-a in this secretory pathway.
Main Methods:
- Co-immunoprecipitation assays in COS-7 cells to identify protein interactions.
- Systematic investigation of interactions between Slp4-a, syntaxins (1-5), and Munc18s (1-3).
- Deletion analysis to map the binding site of Slp4-a for syntaxin/Munc18, and functional assays using antibodies in permeabilized parotid acinar cells.
Main Results:
- Slp4-a interacts with a closed conformation of syntaxin-2/3 in a Munc18-2-dependent manner.
- Slp4-a strongly interacts with Munc18-1, and syntaxin-2/3 co-immunoprecipitates with Slp4-a only in the presence of Munc18-1/2.
- A novel linker domain (amino acid residues 144-354) of Slp4-a mediates binding to syntaxin-2/3 and Munc18-1/2. The Slp4-a.syntaxin-2 complex is present in rat parotid glands.
- Antibody against the Slp4-a linker domain inhibits isoproterenol-stimulated amylase release from parotid acinar cells.
Conclusions:
- Slp4-a modulates amylase release from parotid acinar cells via interaction with syntaxin-2/3 on the apical plasma membrane.
- The findings reveal a novel mechanism for exocytosis regulation in salivary glands involving Slp4-a, syntaxin-2/3, and Munc18 proteins.
- The linker domain of Slp4-a is critical for its interaction with the exocytotic machinery in parotid acinar cells.