@article {866, title = {Detection of a Yb3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {93}, year = {1996}, month = {1996 Dec 10}, pages = {14333-7}, 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.}, keywords = {Bacteriorhodopsins, Binding Sites, Metals, Rare Earth, Phospholipids, Retinaldehyde, Spectroscopy, Near-Infrared}, issn = {0027-8424}, author = {Roselli, Cecile and Boussac, A and Mattioli, T A and Griffiths, Jennifer A. and El-Sayed, Mostafa A} } @article {1271, title = {Monodentate vs Bidentate Binding of Lanthanide Cations to PO2- in Bacteriorhodopsin}, journal = {The Journal of Physical Chemistry}, volume = {100}, year = {1996}, note = {doi: 10.1021/jp9533279}, month = {1996}, pages = {6863 - 6866}, publisher = {American Chemical Society}, abstract = {The frequency difference between the symmetric and antisymmetric stretching vibration of PO2- in phosphatidylglycerol phospate (PGP) is used to differentiate between monodentate and bidentate binding of these groups to metal cations in the membrane of bacteriorhodopsin (bR) and phosphatidylglycerol phospate. The binding of Ca2+ to PGP is found to have a frequency difference corresponding to monodentate binding. The symmetric and antisymmetric PO2- bands in bR show similar frequency shifts upon Ca2+ binding, which is independent of pH. This suggests that Ca2+ has a monodentate type binding with the PO2- in bR. In contrast, the PO2- symmetric and antisymmetric frequencies of PGP complexes with trivalent lanthanide cations with higher charge density (Ho3+ and Dy3+) are observed to have smaller separations and to increase their separation with increasing pH toward the value observed for Ca2+ binding. Lanthanide cations (Ho3+, Dy3+, Eu3+, Nd3+, and La3+) binding in bR at pH 4 show small frequency separations that are observed to have similar frequency shifts with pH, the magnitude of which is dependent on the cation. It is proposed that at low pH the lanthanide cations with higher charge density have bidentate binding to bR, while at high pH, complexation with the OH- competes with one of the oxygens of the PO2- for the binding of the lanthanide ion thus changing the bidentate to monodentate type binding.The frequency difference between the symmetric and antisymmetric stretching vibration of PO2- in phosphatidylglycerol phospate (PGP) is used to differentiate between monodentate and bidentate binding of these groups to metal cations in the membrane of bacteriorhodopsin (bR) and phosphatidylglycerol phospate. The binding of Ca2+ to PGP is found to have a frequency difference corresponding to monodentate binding. The symmetric and antisymmetric PO2- bands in bR show similar frequency shifts upon Ca2+ binding, which is independent of pH. This suggests that Ca2+ has a monodentate type binding with the PO2- in bR. In contrast, the PO2- symmetric and antisymmetric frequencies of PGP complexes with trivalent lanthanide cations with higher charge density (Ho3+ and Dy3+) are observed to have smaller separations and to increase their separation with increasing pH toward the value observed for Ca2+ binding. Lanthanide cations (Ho3+, Dy3+, Eu3+, Nd3+, and La3+) binding in bR at pH 4 show small frequency separations that are observed to have similar frequency shifts with pH, the magnitude of which is dependent on the cation. It is proposed that at low pH the lanthanide cations with higher charge density have bidentate binding to bR, while at high pH, complexation with the OH- competes with one of the oxygens of the PO2- for the binding of the lanthanide ion thus changing the bidentate to monodentate type binding.}, isbn = {0022-3654}, doi = {doi: 10.1021/jp9533279}, url = {http://dx.doi.org/10.1021/jp9533279}, author = {Griffiths, Jennifer A. and Masciangioli, Tina M. and Roselli, Cecile and El-Sayed, Mostafa A} }