title: Detection of a Yb3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups.
abstract: 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.
authors.affiliation: Section de Bioénergetique, Commissariat á l'Energie Atomique Saclay, Gif-sur-Yvette, France.
authors.forename: C
authors.initials: C
authors.lastname: Roselli
authors.forename: A
authors.initials: A
authors.lastname: Boussac
authors.forename: T A
authors.initials: TA
authors.lastname: Mattioli
authors.forename: J A
authors.initials: JA
authors.lastname: Griffiths
authors.forename: M A
authors.initials: MA
authors.lastname: el-Sayed
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D008674:Metals, Rare Earth / Q000737:chemistry* / Q000378:metabolism; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D012172:Retinaldehyde; D019265:Spectroscopy, Near-Infrared
chemical_list: D008674:Metals, Rare Earth; D010743:Phospholipids; D001436:Bacteriorhodopsins; D012172:Retinaldehyde