Comparative structural aspects of cation binding to phosphatidylserine bilayers

Area of Science:

• Biophysics
• Materials Science
• Structural Biology

Background:

• Phosphatidylserines (PS) are crucial zwitterionic phospholipids with a net negative charge at physiological pH.
• The structural organization of lipid bilayers, particularly phosphatidylserines, is influenced by hydration and ionic environment.
• Understanding PS bilayer structures is vital for cell membrane function and biomaterial design.

Purpose of the Study:

• To investigate the structural patterns of phosphatidylserine (PS) bilayers upon complexation with various monovalent and divalent cations.
• To determine the effect of cation type and hydration state on PS bilayer structure using X-ray diffraction.

Main Methods:

• X-ray diffraction analysis was performed on a series of phosphatidylserines (PS) with varying chain lengths.
• Data were collected for anhydrous acidic PS, anhydrous K+-PS, and hydrated PS complexed with Li+, Mg2+, Ca2+, Sr2+, Ba2+, and Pr3+.

Main Results:

• A simple structural pattern was observed across different PS complexes.
• Two distinct bilayer structural types were identified: one with untilted hydrocarbon chains (form I) and another with tilted chains (form II).
• Complexation with Li+, Mg2+, Ca2+, and other divalent cations induced dehydration of the PS bilayers, leading to the adoption of either form I or form II structures.

Conclusions:

• Phosphatidylserine bilayers exhibit a limited structural polymorphism, primarily characterized by chain tilt, irrespective of chain length.
• Cation complexation, especially with divalent cations, plays a significant role in modulating PS bilayer structure through dehydration.
• The observed structural forms (I and II) provide insights into the packing arrangements and conformational states of PS bilayers in different ionic conditions.