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Golgi coatomer binds, and forms K(+)-selective channels gated by, inositol polyphosphates
B Fleischer1, J Xie, M Mayrleitner
1Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235.
The Journal of Biological Chemistry
|July 8, 1994
Summary
Coatomer binds inositol polyphosphates with high affinity and exhibits ion channel activity. This activity is modulated by specific inositol polyphosphates, suggesting a role in cellular transport.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Coatomer is a protein complex essential for Golgi vesicle formation and transport.
- Inositol polyphosphates are signaling molecules involved in various cellular processes.
Purpose of the Study:
- To investigate the binding interactions between coatomer and inositol polyphosphates.
- To characterize the ion channel activity of coatomer and its regulation by inositol polyphosphates.
Main Methods:
- Purification of coatomer from bovine liver cytosol.
- Direct binding assays using various inositol polyphosphates.
- Reconstitution of coatomer into planar lipid bilayers to assess ion channel activity.
Main Results:
- Coatomer exhibits subnanomolar affinity for inositol 1,3,4,5-tetrakisphosphate ((1,3,4,5)IP4) and inositol hexakisphosphate (IP6).
- Diphosphoinositol pentakisphosphate (PP-IP5) efficiently competes for these binding sites.
- Reconstituted coatomer forms a cation-selective ion channel, preferentially permeable to K+.
- Channel activity is selectively blocked or modulated by (1,3,4,5)IP4, IP6, and PP-IP5, but not by (1,4,5)IP3 or (1,3,4,5,6)IP5.
Conclusions:
- Coatomer possesses specific binding sites for certain inositol polyphosphates.
- The ion channel activity of coatomer is directly modulated by these bound inositol polyphosphates.
- This suggests a novel regulatory mechanism for coatomer function in Golgi transport.