Intermolecular chelation of two serine phosphates by Ca2+ and Mg2+. A theoretical structural investigation.

The modes of interaction of Ca2+ and Mg2+ with 11 pre-selected conformations of serine phosphate (SP) are investigated by using an additive procedure based on ab initio Self Consistent Field computations for the calculation of intermolecular interaction energies. Possible models for the arrangements, SP-Ca2+-SP and SP-Mg2+-SP, are investigated. The comparison between the binding energetics of Mc2+ and Ca2+ to one and two serine phosphates is discussed. It appears that some specific arrangements, SP-M2+-SP (M2+ =Ca2+ or Mg2+), are able to account for the displayed marked selectivity of phosphatidylserine for Ca2+, in keeping with the distinctive features of this complex in model membranes.