Physiological Calcium Concentrations Slow Dynamics at the Lipid-Water Interface.

Area of Science:

• Biophysics
• Membrane Biophysics
• Physical Chemistry

Background:

• Phospholipids interact with ions, altering membrane properties.
• Calcium ions (Ca2+) are crucial in biological systems and can affect cell membranes.

Purpose of the Study:

• To investigate the effects of calcium ions on phospholipid membrane dynamics.
• To elucidate the role of phosphatidylserine in Ca2+-induced changes.

Main Methods:

• Time-resolved ultrafast two-dimensional infrared spectroscopy.
• Molecular dynamics simulations.
• Label-free probing of local water dynamics using ester groups.

Main Results:

• Millimolar Ca2+ concentrations significantly slow local water dynamics at the lipid-water interface.
• This effect is specific to membranes containing anionic phosphatidylserine, not zwitterionic phosphatidylcholine.
• Ca2+ was observed to bind primarily to the carboxylate group of phosphatidylserines.
• Water dynamics were up to 50% slower with 2.5 mM Ca2+.

Conclusions:

• Divalent cations like Ca2+ can modulate membrane dynamics by interacting with anionic phospholipids.
• These findings are relevant to understanding cellular processes like apoptosis and the biophysical effects of cations on lipid bilayers.