Redistribution of terbium ions across acetylcholine receptor-enriched membranes induced by agonist desensitization.
Using small-angle x-ray diffraction from centrifugally oriented acetylcholine receptor (AChR) enriched membranes coupled with anomalous scattering from terbium ions (Tb3+) titrated into presumed Ca2+ binding sites, we have mapped the distribution of Tb3+ perpendicular to the membrane plane using a heavy atom refinement algorithm. We have compared the distribution of Tb3+ in the closed resting state with that in the carbamylcholine-desensitized state. In the closed resting state we find 45 Tb3+ ions distributed in 10 narrow peaks perpendicular to the membrane plane. Applying the same refinement procedure to the data from carbamylcholine desensitized AChR we find 18 fewer Tb3+ ions in eight peaks, and slight rearrangements of Tb3+ density in the peaks near the ends of the AChR ion channel pore. These agonist dependent changes in the Tb3+ stoichiometry and distribution suggest a likely role for multivalent cations in stabilizing the different functional states of the AChR, and the changes in the Tb3+ distribution at the two ends of the pore suggest a potential role for multivalent cations in the gating of the ion channel.
Department of Information Technology, Gilead Sciences, Foster City, California, USA.
Thomas E
TE
Lee
Anthony R
AR
Chuang
Matthew S
MS
Marek
Sebastian
S
Doniach
Robert H
RH
Fairclough
D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D018679:Cholinergic Agonists / Q000494:pharmacology*; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism; D044367:Phase Transition; D016062:Porosity; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D011950:Receptors, Cholinergic / Q000737:chemistry / Q000378:metabolism*; D053838:Scattering, Small Angle; D013725:Terbium / Q000378:metabolism* / Q000494:pharmacology; D017186:Titrimetry; D014101:Torpedo; D014961:X-Ray Diffraction
D018679:Cholinergic Agonists; D007473:Ion Channels; D011950:Receptors, Cholinergic; D013725:Terbium; D002217:Carbachol