On the coordination of La super(3+) by phosphatidylserine

In a recent study by Bentz, J., D. Alford, J. Cohen, and N. Duezguenes, La super(3+) was found to be more effective than Ca super(2+) in causing nonleaky fusion of phosphatidylserine vesicles. It was proposed that this difference in fusion efficiency may be due, in part, to a difference in coordination of the two cations. That is, Ca super(2+) was presumed to bind to the lipid phosphate, whereas La super(3+) was proposed to be coordinated by the serine carboxylate and amine. super(31)P and super(13)C NMR results presented here demonstrate that the lanthanides, Tb super(3+) and La super(3+), are coordinated by the phosphodiester and carboxylate moieties of phosphatidylserine. The work presented here also demonstrates that La super(3+) affects the inner surface phosphodiesters differently than those on the outer surface of phosphatidylserine vesicles. Higher levels of bound La super(3+) on the outer surface may be required to induce the same changes in headgroup conformation.