Tensile forces and shape entropy explain observed crista structure in mitochondria

Area of Science:

• Biophysics
• Cell Biology
• Structural Biology

Background:

• The inner mitochondrial membrane's morphology is crucial for cellular energy production.
• Its complex structure, featuring both tubular and lamellar cristae, is not fully understood.
• Understanding this structure is key to comprehending mitochondrial function.

Purpose of the Study:

• To develop a biophysical model explaining the self-assembly of the inner mitochondrial membrane.
• To investigate the energetic contributions, including protein tension and entropic factors, that shape mitochondrial cristae.
• To correlate theoretical predictions with experimental observations of mitochondrial structure.

Main Methods:

• Development of a free energy minimization model incorporating bending, surface area, pressure, protein tension, and entropic terms.
• Three-dimensional electron tomography of mitochondria in HeLa cells and mouse embryonic fibroblasts.
• Quantitative analysis of tomographic data to measure structural features.

Main Results:

• The model successfully infers the observed inner mitochondrial membrane morphology.
• Tensile forces of approximately 20 pN are predicted to stabilize the coexistence of tubular and lamellar cristae.
• A pressure difference of -0.036 ± 0.004 atm and surface tension of 0.09 ± 0.04 pN/nm were predicted.

Conclusions:

• The inner mitochondrial membrane's complex morphology is a result of free energy minimization.
• Protein-exerted tension plays a significant role in stabilizing the observed crista structures.
• The biophysical model provides a framework for understanding the relationship between molecular forces and mitochondrial architecture.