Detection of a Yb3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups.
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.
Roselli
C
C
Section de Bioénergetique, Commissariat á l'Energie Atomique Saclay, Gif-sur-Yvette, France.
Boussac
A
A
Mattioli
T A
TA
Griffiths
J A
JA
el-Sayed
M A
MA
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
D008674:Metals, Rare Earth; D010743:Phospholipids; D001436:Bacteriorhodopsins; D012172:Retinaldehyde