Jake Pushie, University of Saskatchewan

Abstract:

Disruption in extracellular Cu homeostasis is linked to fatal genetic disorders, cancer, multiple neurodegenerative diseases and other dysfunctions in human health. Multiple biologically accessible oxidation states allow Cu to participate in redox reactions and thus serve as a cofactor in electron transfer reactions that are essential to sustain life. The chemical nature of Cu is a double-edged sword, however, as the redox chemistry that makes Cu and indispensable transition metal ion is biological systems is also that which makes it potentially toxic. Cu reactions can generate reactive oxygen species through Fenton-tyle chemistry, resulting in oxidative damage and cell-death. Sophisticated mechanisms have therefore evolved to control this essential, and potentially toxic, metal.

Most of the Cu present in human blood is non-exchangeable and is tightly bound by the ferroxidase enzyme, ceruloplasmin. A small fraction of Cu trafficked in the blood is exchangeable and can be taken up by human cells through transfer to copper transport proteins or other cellular Cu acquisition proteins. This exchangeable pool of Cu is bound primarily to human
serum albumin (HSA), with a small proportion also bound to other low molecular weight complexes. HSA is the most abundant protein in human blood plasma and cerebrospinal fluid and is responsible for Cu transport and homeostasis in the blood stream as well as delivery to target organs.

A major assumption is that Cu bound to HSA is in the Cu(II) oxidation state; thus, interactions between HSA and Cu(II) have been intensely investigated for over a century – due in large part to the coloured Cu(II)HSA complexes that form. Mild reducing agents are sufficient to reduce Cu(II) to Cu(I) in the presence of HSA however and our work was the first to characterize a stable form of reduced Cu bound to HAS, which forms a 2-cordinate bis-histidine complex with high binding affinity. The high affinity for Cu(I) suggests that interactions between this metal and HSA in human extracellular fluids are likely to play a significant role in Cu homeostasis and trafficking.

Using a combination of Cu K-edge X-ray absorption fine structure (EXAFS) spectroscopy, high energy resolution fluorescence detection (HERFD), density functional structure calculations, and molecular dynamics (MD) simulations, we have mapped the potential Cu(I) binding sites in HSA. Structure calculations also provide mechanistic insights into the nature of the local HSA
structural rearrangements that facilitate formation of the highly stable bis-histidine Cu(I) site upon reduction of Cu(II). Results from MD simulations also reveal a network of multiple potential bis-histidine sites in HAS that may further facilitate Cu(I) trafficking.

Poster Session Link: https://gather.town/invite?token=0pEoq7VP

If you have any questions for the presenter, please contact them via email: jake.pushie@usask.ca