Intermediate Cu^IIATCUN Species Reacts With Biomolecules Within Time Windows of Biological Processes

Area of Science:

• Biochemistry
• Metalloprotein Chemistry
• Biophysical Chemistry

Background:

• The ATCUN motif (N-terminal Xaa-Zaa-His) binds Cu(II) in a square-planar geometry.
• Its abundance in the human proteome and unique copper-binding properties are well-established.
• The apparent inertness of Cu(II)ATCUN complexes contrasts with dynamic biological copper balance.

Purpose of the Study:

• To investigate the multi-step nature of Cu(II) binding to ATCUN sequences.
• To directly assess the reactivity of transient copper-binding intermediates.
• To explore the role of these intermediates in biological copper redox and exchange reactions.

Main Methods:

• Utilized double mixing stopped-flow experiments.
• Employed a model tetrapeptide (DAHK) representing the ATCUN motif of Human Serum Albumin.
• Analyzed the exchange and reduction kinetics of copper complexes.

Main Results:

• Identified partially coordinated intermediate species in Cu(II) binding to ATCUN sequences.
• Demonstrated that a transient 2N intermediate readily exchanges Cu(II) with histidine.
• Showed rapid reduction of the 2N intermediate to Cu(I) by glutathione.

Conclusions:

• Transient Cu(II)ATCUN intermediates exhibit distinct reactivity compared to the final 4N complex.
• These intermediates are capable of rapid copper exchange and reduction.
• Findings necessitate a re-evaluation of the physiological roles of ATCUN motifs in copper homeostasis.