Structural and functional characterization of an inositol polyphosphate receptor from cerebellum.
An inositol polyphosphate receptor has been purified from bovine cerebellum which consists of three different polypeptides with Mr of 111,000, 102,000, and 52,000. Negative staining electron microscopy reveals globular-like structures 10-13 nm in diameter. The receptor has a Stokes radius of 400,000 daltons as determined by molecular sieve high performance liquid chromatography. The receptor preparation binds inositol 1,3,4,5-tetrakisphosphate, inositol hexaphosphate (or phytol), and inositol 1,4,5-trisphosphate (IP4, IP6, and IP3, respectively) with submicromolar affinity (0.19, 0.15, and 0.54 microM, respectively) at conditions approximating physiological ionic strength and pH. The purified receptor preparation, when reconstituted into planar bilayers, displays ion channel activity, preferentially permeable to K+. Permeability ratios of the channel are PK+/PNa+ approximately 5 and PK+/PCl approximately 19. In symmetrical 100 mM KCl, the channel is characterized by long open times (minutes) with a conductance of 7.2 picosiemens. The channel is selectively modulated by IP4. That is, at 1 microM IP4, the mean open time decreased substantially to rapid flicker behavior and the channel is completely closed at 10 microM IP4. IP6 and IP3 did not modulate the channel under similar conditions. Thus, the channel appears to be an IP4-modulated K+ channel.
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235.
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Chadwick
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Timerman
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Saito
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Mayrleitner
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Schindler
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Fleischer
D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D002531:Cerebellum / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D008564:Membrane Potentials; D008854:Microscopy, Electron; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D008970:Molecular Weight; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D014316:Tritium
D007295:Inositol Phosphates; D007473:Ion Channels; D008051:Lipid Bilayers; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; C072844:inositol polyphosphate receptor; D014316:Tritium