Open AccessDetection of a Yb 3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups
Author(s) -
Cécile Roselli,
Alain Boussac,
Tony A. Mattioli,
Jennifer Griffiths,
Mostafa A. ElSayed
Publication year - 1996
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.93.25.14333
Subject(s) - bacteriorhodopsin , chemistry , denticity , lanthanide , binding site , terbium , fluorescence , crystallography , halobacteriaceae , phospholipid , fluorescence spectroscopy , ion , membrane , stereochemistry , halobacterium salinarum , crystal structure , biochemistry , organic chemistry , physics , quantum mechanics
Near infrared Yb3+ vibronic sideband spectroscopy was used to characterize specific lanthanide binding sites in bacteriorhodopsin (bR) and retinal free bacteriorhodopsin (bO). The VSB spectra for deionized bO regenerated with a ratio of 1:1 and 2:1 ion to bO are identical. Application of a two-dimensional anti-correlation technique suggests that only a single Yb3+ site is observed. The Yb3+ binding site in bO is observed to consist of PO2 − groups and carboxylic acid groups, both of which are bound in a bidentate manner. An additional contribution most likely arising from a phenolic group is also observed. This implies that the ligands for the observed single binding site are the lipid head groups and amino acid residues. The vibronic sidebands of Yb3+ in deionized bR regenerated at a ratio of 2:1 ion to bR are essentially identical to those in bO. The other high-affinity binding site is thus either not evident or its fluorescence is quenched. A discussion is given on the difference in binding of Ca2+ (or Mg2+ ) and lanthanides in phospholipid membrane proteins.