| Abstract: |
Coatomer is a distinct type of coat protein complex involved in the formation of specific Golgi intercisternal transport vesicles. Direct binding studies using purified coatomer isolated from bovine liver cytosol show that coatomer specifically binds both inositol 1,3,4,5-tetrakisphosphate ((1,3,4,5)IP4) and inositol hexakisphosphate (IP6) with subnanomolar affinities (0.1 and 0.2 nM, respectively). Diphosphoinositol pentakisphosphate (PP-IP5) is an efficient competitor for both (1,3,4,5)IP4 and IP6 binding to coatomer. Inositol 1,3,4,5,6-pentakisphosphate ((1,3,4,5,6)IP5) is a poor inhibitor of IP6 binding, whereas little or no competition is detected with inositol 1,4,5-trisphosphate ((1,4,5)I-P3). Coatomer displays ion channel activity when reconstituted into planar bilayers which is preferentially permeable to K+. Permeability ratios of the channel are P(K+)/P(Cl-) ~8.0 and P(K+)/P(Na+) ~7.1, indicating a cation-selective channel with selectivity of K+ over Na+. In symmetrical 500 mM KCl, the smallest observable unitary channel conductance is 8.3 picosiemens. The coatomer channel activity is normally active with long open times (0.1 to several seconds) and is selectively blocked by 10 μM (1,3,4,5)IP4, 1 μM IP6, and 0.27 μM PP-IP5; even lower concentrations are sufficient to induce channel flicker. The channel activity is not affected by (1,4,5)IP3, or (1,3,4,5,6)IP5. Thus, the channel activity of coatomer is modulated by the inositol polyphosphates which exhibit tight binding to the complex. |
| Keywords: |
nonhuman; animal cell; animal; cell line; membrane proteins; animalia; cattle; lipid bilayers; lipid bilayer; phospholipids; golgi complex; cell vacuole; bovinae; coatomer protein; channel gating; ion channel gating; golgi apparatus; coat protein; potassium channel; potassium transport; cow; priority journal; article; potassium channels; inositol polyphosphate; inositol phosphates; support, non-u.s. gov't; support, u.s. gov't, p.h.s.; support, u.s. gov't, non-p.h.s.; liver cytosol; potassium conductance
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