Stable mitochondrial CICIII₂ supercomplex interactions in reptiles versus homeothermic vertebrates

Area of Science:

• Mitochondrial bioenergetics
• Comparative physiology
• Molecular biology

Background:

• Mitochondrial electron transport chain complexes (CI, CIII, CIV) form supercomplexes (SCs).
• The function of SCs is debated, with hypotheses including improved electron transfer, reduced reactive oxygen species (ROS), and enhanced stability.
• Previous studies on SCs focused mainly on mammals.

Purpose of the Study:

• To investigate the stability, composition, and activity of mitochondrial SCs across diverse vertebrate classes.
• To identify patterns of SC variation between endotherms and ectotherms.
• To explore the adaptive significance of SC stability in relation to body temperature.

Main Methods:

• Solubilization of mitochondrial supercomplexes using DDM detergent.
• Mass-spectrometric complexomics for SC composition analysis.
• Measurement of mitochondrial respiration rates and H2O2 production.

Main Results:

• Mitochondrial CICIII2 SCs were unstable in endotherms (birds, mammals) but highly stable in reptiles.
• In turtles, CICIII2 was the predominant SC, with 90% of CI incorporated.
• Stable SCs did not correlate with reduced H2O2 production or increased respiration rates.

Conclusions:

• SC stability significantly varies among vertebrate classes, being highest in reptiles and lowest in endotherms.
• The observed pattern suggests SC stability is an adaptation to different body temperatures.
• The findings do not support a direct role of SCs in electron transfer enhancement or ROS prevention.