Effects of zinc on creatine kinase: activity changes, conformational changes, and aggregation

Area of Science:

• Biochemistry
• Enzymology
• Metalloprotein

Background:

• Creatine kinase (CK) is crucial for cellular energy metabolism.
• The influence of bivalent metal ions on CK activity and structure is well-documented.
• Zinc's specific interactions with CK require further elucidation.

Purpose of the Study:

• To investigate the distinct effects of zinc on creatine kinase (CK) activity, conformation, and aggregation.
• To determine the concentration-dependent impact of zinc on CK stability and function.
• To propose a mechanism for zinc-induced CK aggregation and its relevance to Alzheimer's disease.

Main Methods:

• Enzyme activity assays were performed to measure CK activity.
• Spectroscopic techniques (e.g., circular dichroism) were used to assess conformational changes (hydrophobic surface exposure, alpha-helix content).
• Kinetic analyses determined rate constants for inactivation and conformational changes.
• Aggregation was monitored under varying zinc, CK, and temperature conditions.

Main Results:

• Zinc up to 0.1 mM increased CK activity, hydrophobic exposure, and alpha-helix content.
• Zinc above 0.1 mM led to CK denaturation and inactivation.
• At 0.1 mM zinc, CK activity was near native levels, but conformation was altered.
• Zinc concentrations over 0.05 mM induced CK aggregation, dependent on zinc, CK, and temperature.
• EDTA reversed both inactivation and aggregation.

Conclusions:

• Zinc exhibits a biphasic effect on CK, enhancing activity at low concentrations and causing denaturation/inactivation at higher concentrations.
• Zinc induces CK aggregation through concentration, temperature, and protein-dependent mechanisms.
• The findings provide insights into CK abnormalities in Alzheimer's disease and suggest a role for zinc dysregulation.