Oxaliplatin Binding to Human Copper Chaperone Atox1 and Protein Dimerization

Area of Science:

• Biochemistry
• Metalloprotein Chemistry
• Anticancer Drug Research

Background:

• Copper trafficking proteins, like Atox1, are involved in cellular responses to platinum anticancer drugs.
• Oxaliplatin, a platinum-based chemotherapy agent, features a 1,2-diaminocyclohexane (DACH) ligand, making it more stable than cisplatin.
• Understanding Atox1's interaction with oxaliplatin is crucial for elucidating platinum drug resistance mechanisms.

Purpose of the Study:

• To investigate the reaction between the copper chaperone Atox1 and an activated form of oxaliplatin.
• To characterize the structural changes and binding modes of Atox1 upon interaction with platinum drug moieties.
• To reconcile discrepancies between solution-phase behavior and crystallographic data of Atox1-platinum complexes.

Main Methods:

• In vitro reaction of purified Atox1 with activated oxaliplatin.
• Spectroscopic and crystallographic analyses to determine complex structures.
• Comparative analysis with existing structural data for Atox1-metal complexes.

Main Results:

• Atox1 binds {Pt(DACH)2+} moieties in solution, forming monomeric and dimeric species with potential bridging sulfur atoms.
• A dimeric Atox1-platinum complex (Atox12·Pt2+) forms in solution, accompanied by protein unfolding and loss of diamine ligands.
• Crystallization yielded a dimeric Atox1 species with two platinum-binding sites, but with lower occupancy than expected, suggesting co-occupation by copper ions.

Conclusions:

• The interaction of Atox1 with oxaliplatin leads to distinct structural outcomes in solution versus the solid state.
• A novel hypothesis suggests copper ions occupy residual binding sites in platinum-Atox1 crystal structures, integrating prior conflicting data.
• This finding may have implications for understanding platinum drug interactions with cellular copper chaperones and potential resistance mechanisms.