Biophysical Journal 50: 277-284 (1986)
© 1986 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Katre, N V Articles by Stroud, R M Search for Related Content PubMed PubMed Citation Articles by Katre, N V Articles by Stroud, R M

Cation binding sites on the projected structure of bacteriorhodopsin.

ABSTRACT

Divalent cations are involved in the function of bacteriorhodopsin (bR) as a light-driven proton pump. If cations are removed from purple membranes they become blue. Divalent cations such as Ca2+ or Pb2+ or trivalent ions, can be stoichiometrically titrated back on to these deionized membranes. The color transitions as a function of ion concentration for Ca2+ or Pb2+ are precisely comparable and indicate that approximately three stoichiometric equivalents of cations are required to effect the color transition (Kimura et al., 1984). We found four main partially occupied binding sites for cations at a stoichiometric ratio of 3 Pb2+/bR. We localized the binding sites for Pb2+ using x-ray diffraction of membranes reconstituted with 1, 2, and 3 equivalents of Pb2+ per bR. The site of highest affinity is located on helix 7. At 2 Pb2+/bR, sites on helix 6 and between helix 2 and 3 are occupied. At 3 Pb2+/bR a fourth site above helix 3 is occupied.

This article has been cited by other articles:

				C. Roselli, A. Boussac, T. A. Mattioli, J. A. Griffiths, and M. A. El-Sayed Detection of a Yb3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups PNAS, December 10, 1996; 93(25): 14333 - 14337. [Abstract] [Full Text] [PDF]