Location of terbium binding sites on acetylcholine receptor-enriched membranes

Robert H Fairclough, Richard C. Miake-Lye, Robert M. Stroud, Keith O. Hodgson, Sebastian Doniach

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Acetylcholine receptor-enriched membranes bind 45 terbium cations per receptor. The Tb(III) X-ray scattering factor changes by as much as 30% over a 50 eV range about the L3 absorption edge. We exploit these changes to modulate the contribution of these ions to the X-ray diffraction pattern of oriented receptor-enriched membranes by varying the incident X-ray energy. Difference Fourier analysis of the meridional diffraction amplitudes at two X-ray energies revealed six localized regions of Tb(III) density across the membrane. Most significant is the finding of 18 Tb(III) ions near the entrance and 11 ions near the exit of the ion channel as well as 4 or 5 Tb(III) ions localized in the channel itself. This evidence strongly suggests the presence of anionic carboxylate side-chains on the channel lining.

Original languageEnglish (US)
Pages (from-to)673-680
Number of pages8
JournalJournal of Molecular Biology
Issue number4
StatePublished - Jun 20 1986
Externally publishedYes

ASJC Scopus subject areas

  • Virology


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