Charge-induced tilt in ordered-phase phosphatidylglycerol bilayers evidence from X-ray diffraction

Area of Science:

• Biophysics
• Lipid Bilayer Research
• Structural Biology

Background:

• Dipalmitoyl phosphatidylglycerol (DPPG) is a key phospholipid.
• Lipid bilayer structure is sensitive to environmental factors like pH.
• Understanding lipid organization is crucial for membrane biophysics.

Purpose of the Study:

• To investigate the structural changes in DPPG bilayers under varying pH conditions.
• To determine the effect of pH on lipid packing and molecular orientation.
• To quantify changes in bilayer dimensions and area per lipid.

Main Methods:

• X-ray diffraction was employed to study DPPG bilayers.
• Experiments were conducted at pH 8.0 (charged) and pH 1.5 (protonated).
• Water content and salt concentration were controlled.

Main Results:

• DPPG bilayers remained in an ordered phase across all studied conditions.
• Lamellar repeat distances varied with pH, reaching limiting values of 6.24 nm (pH 8.0) and 6.73 nm (pH 1.5).
• Area per lipid molecule and molecular tilt angle were significantly affected by pH.

Conclusions:

• The protonation state of DPPG influences bilayer structure.
• Lipid molecules are tilted at pH 8.0 and untilted at pH 1.5.
• These findings provide insights into pH-dependent lipid membrane organization.