Surface Morphometrics reveals local membrane thickness variation in organellar subcompartments

Area of Science:

• Cell Biology
• Biophysics
• Structural Biology

Background:

• Lipid bilayers are fundamental to cellular architecture and function.
• Previous studies on lipid bilayers primarily used purified liposomes, limiting in vivo insights.
• Characterizing membrane properties within native cellular environments has been challenging.

Purpose of the Study:

• To develop and validate a method for measuring organellar membrane thickness in situ.
• To investigate variations in membrane thickness within and between cellular organelles.
• To explore the relationship between membrane thickness and other biophysical properties, as well as associated macromolecular complexes.

Main Methods:

• Utilized cellular cryo-electron tomography (cryo-ET) for high-resolution 3D imaging of native cellular structures.
• Expanded the 'Surface Morphometrics' pipeline to quantify membrane thickness by measuring distances between phospholipid head groups.
• Applied the method to various organellar membranes, including the mitochondrial inner membrane.

Main Results:

• Demonstrated significant variations in membrane thickness within and between different organellar membranes.
• Showed a positive correlation between organellar membrane thickness and membrane curvedness.
• Identified distinct membrane thickness profiles in subcompartments of the mitochondrial inner membrane and correlated thickness with macromolecular complex densities.

Conclusions:

• The updated Surface Morphometrics pipeline enables quantitative analysis of membrane thickness in native cellular contexts.
• Organellar membrane thickness is a variable property that correlates with cellular ultrastructure and function.
• This framework facilitates investigation into how altered membrane composition impacts organelle structure and function in health and disease.