title: Phosphatidylserine reversibly binds Cu2+ with extremely high affinity.
abstract: Phosphatidylserine (PS) embedded within supported lipid bilayers was found to bind Cu(2+) from solution with extraordinarily high affinity. In fact, the equilibrium dissociation constant was in the femtomolar range. The resulting complex formed in a 1:2 Cu(2+)-to-PS ratio and quenches a broad spectrum of lipid-bound fluorophores in a reversible and pH-dependent fashion. At acidic pH values, the fluorophores were almost completely unquenched, while at basic pH values significant quenching (85-90%) was observed. The pH at which the transition occurred was dependent on the PS concentration and ranged from approximately pH 5 to 8. The quenching kinetics was slow at low Cu(2+) concentrations and basic pH values (up to several hours), while the unquenching reaction was orders of magnitude more rapid upon lowering the pH. This was consistent with diffusion-limited complex formation at basic pH but rapid dissociation under acidic conditions. The tight binding of Cu(2+) to PS may have physiological consequences under certain circumstances.
authors.affiliation: Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77843, USA.
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Monson
authors.forename: Xiao
authors.initials: X
authors.lastname: Cong
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Robison
authors.forename: Hudson P
authors.initials: HP
authors.lastname: Pace
authors.forename: Chunming
authors.initials: C
authors.lastname: Liu
authors.forename: Matthew F
authors.initials: MF
authors.lastname: Poyton
authors.forename: Paul S
authors.initials: PS
authors.lastname: Cremer
mesh_terms: D002413:Cations, Divalent / Q000378:metabolism; D003300:Copper / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D046210:Microfluidic Analytical Techniques; D010718:Phosphatidylserines / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D008051:Lipid Bilayers; D010718:Phosphatidylserines; D003300:Copper