Aluminum interaction with calmodulin. Evidence for altered structure and function from optical and enzymatic studies

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Calmodulin (CaM) is a crucial calcium-binding protein regulating numerous cellular processes.
• Understanding metal ion interactions with CaM is vital for elucidating cellular signaling pathways.

Purpose of the Study:

• To investigate the binding characteristics and structural effects of aluminum ions on bovine brain calmodulin.
• To compare aluminum's interaction with calmodulin to that of calcium.

Main Methods:

• Fluorescence spectroscopy
• Circular dichroic spectrophotometry
• Equilibrium dialysis
• Enzyme activity assays (calmodulin-dependent phosphodiesterase)

Main Results:

• Aluminum binds stoichiometrically and cooperatively to calmodulin.
• A 2:1 aluminum-to-calmodulin molar ratio induces major structural changes, including helix-coil transitions.
• Aluminum exhibits higher binding affinity than calcium to calmodulin.
• A 4:1 aluminum-to-calmodulin ratio completely inhibits calcium-calmodulin-dependent phosphodiesterase activity.

Conclusions:

• Aluminum ions induce significant structural alterations in calmodulin, impacting its flexibility.
• Aluminum binding profoundly affects calmodulin's function, particularly its interaction with downstream effectors like phosphodiesterase.