Protein-Driven Copper Redox Regulation: Uncovering the Role of Disulphide Bonds and Allosteric Modulation

Area of Science:

• Biochemistry
• Biophysics
• Metalloprotein chemistry

Background:

• Copper is vital for cellular functions but toxic when redox balance is lost.
• Protein-mediated copper reduction was previously linked to unfolded or amyloid structures.

Purpose of the Study:

• To investigate the mechanism of Cu(II) reduction by the well-folded plasma protein human serum albumin (HSA).
• To explore the role of protein structure and disulphide bonds in copper redox reactions.

Main Methods:

• X-ray absorption spectroscopy (XAS)
• Small-angle X-ray scattering (SAXS)
• Circular dichroism (CD)
• Computational simulations

Main Results:

• HSA intrinsically reduces Cu(II) to Cu(I) through a mechanism involving the Cys392-Cys438 disulphide bond in domain III.
• Copper binding at the ATCUN motif may expose the disulphide bond, facilitating thiol-mediated electron transfer.
• Tetrathiomolybdate (TTM) chelation inhibits this reduction.
• Accessible disulphide bonds and native folded structure are crucial for protein-mediated copper reduction.

Conclusions:

• A novel mechanism for protein-mediated copper reduction by folded proteins is identified.
• Disulphide bond regulation of redox switching plays a significant role in metal homeostasis.
• This mechanism may be generalizable to other globular proteins like SOD1.