Purification of a presynaptic membrane protein that mediates a calcium-dependent translocation of acetylcholine
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Abstract:
A protein, which we call "mediatophore," that mediates calcium-dependent release of acetylcholine from proteoliposomes has been purified from the presynaptic plasma membrane. About 250 micrograms of this material was obtained from 500 g of Torpedo marmorata electric organ. Precipitation of the protein and subsequent removal of associated lipids inactivated the protein, which then became water soluble; this permitted evaluation of its Stokes radius (52 A) and its sedimentation coefficient (9.8 +/- 0.75 S) and, hence, an approximate molecular mass of 210 +/- 16 kDa could be determined. PAGE analysis showed that the protein is made of 17-kDa subunits, not linked by disulfide bonds. When this material was observed by electron microscopy after negative staining, the apparently pentameric structures had an average diameter of about 7 nm.
Insights
Researchers purified a novel protein, mediatophore, essential for calcium-dependent acetylcholine release from presynaptic membranes. This protein plays a key role in neurotransmission.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Acetylcholine release from presynaptic terminals is a critical process in neurotransmission.
- Calcium-dependent mechanisms regulate the release of neurotransmitters like acetylcholine.
- The specific proteins involved in mediating this calcium-dependent release are not fully characterized.
Purpose of the Study:
- To purify and characterize the protein responsible for mediating calcium-dependent acetylcholine release.
- To investigate the structural and molecular properties of this newly identified protein.
Main Methods:
- Purification of the protein from Torpedo marmorata electric organ presynaptic plasma membrane.
- Biochemical analysis including precipitation, lipid removal, Stokes radius and sedimentation coefficient determination.
- Polyacrylamide gel electrophoresis (PAGE) and electron microscopy (negative staining) for structural analysis.
Main Results:
- A protein, termed 'mediatophore,' was purified, mediating calcium-dependent acetylcholine release.
- Purified mediatophore has a molecular mass of approximately 210 ± 16 kDa and a Stokes radius of 52 Å.
- Electron microscopy revealed pentameric structures (7 nm diameter) composed of 17-kDa subunits.
Conclusions:
- Mediatophore is a novel protein complex involved in the release of acetylcholine.
- The protein's structure consists of multiple 17-kDa subunits, forming pentameric complexes.
- This finding provides new insights into the molecular machinery of synaptic transmission.