Protein stability and the evolution of the cell membrane

Area of Science:

• Biochemistry
• Cell Biology
• Membrane Biophysics

Background:

• Cholesterol's role in regulating membrane protein activity is crucial for ion homeostasis.
• Understanding lipid-protein interactions is key to comprehending membrane function and evolution.
• Evolutionary adaptations in membrane composition influence protein behavior and cellular processes.

Purpose of the Study:

• To investigate the effect of cholesterol on the Ca(2+),Mg(2+)-ATPase activity in calf ventricular muscle plasma membranes.
• To determine how temperature influences cholesterol's interaction with the Ca(2+),Mg(2+)-ATPase.
• To elucidate cholesterol's role in protein stabilization and thermal protection.

Main Methods:

• Preparation of plasma membranes from calf ventricular muscle.
• Assay of Ca(2+),Mg(2+)-ATPase catalytic activity at varying temperatures.
• Analysis of enzyme inactivation rates and activation energy in the presence and absence of cholesterol.

Main Results:

• Cholesterol partially inhibits Ca(2+),Mg(2+)-ATPase activity below 42°C.
• Cholesterol promotes enzyme stabilization and higher activity above 42°C.
• Cholesterol-enriched membranes exhibit decreased inactivation rates and reduced energy release at elevated temperatures, indicating thermal protection.

Conclusions:

• Cholesterol modulates Ca(2+),Mg(2+)-ATPase activity in a temperature-dependent manner.
• Cholesterol enhances the thermal stability of the Ca(2+),Mg(2+)-ATPase, protecting it from inactivation.
• This suggests cholesterol's evolutionary role in promoting protein thermostability within eukaryotic cell membranes.