Dimer-dimer interactions in octameric mitochondrial creatine kinase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Mitochondrial creatine kinase (Mi-CK) exists as interconvertible octamers and dimers.
• Understanding Mi-CK oligomerization is crucial for elucidating its role in cellular energy metabolism.

Purpose of the Study:

• Investigate the kinetic and thermodynamic stability of wild-type and mutant chicken sarcomeric Mi-CK octamers.
• Identify factors regulating the in vivo octamer/dimer ratio and the nature of octamer-stabilizing interactions.

Main Methods:

• Kinetic and thermodynamic analysis of wild-type and mutant Mi-CK.
• Experiments conducted at varying temperatures, pH, salt, and substrate concentrations.
• Utilized transition state analogue complex (TSAC) to probe octamer decay.

Main Results:

• Octamer decay accelerated with increasing temperature (up to 28°C) and pH for wild-type Mi-CK.
• Substrate binding and TSAC induced octamer-destabilizing conformations.
• Hydrophobic and polar interactions stabilize octamers; hydrophobic interactions dominate.
• Mutant W264C showed altered temperature dependence, suggesting abolished hydrophobic interactions.

Conclusions:

• Mi-CK octamer-dimer transitions are likely involved in slow, long-term modulations of mitochondrial energy metabolism, not rapid regulation.
• Hydrophobic interactions play a significant role in maintaining Mi-CK octamer stability.