RUI: Understanding Cu(I) Interactions with Zinc-Metalloproteins: Impact of Cu(I) on Structure and Function of the X-Linked Inhibitor of Apoptosis Protein

Macalester College, Saint Paul MN

Investigators

Abstract

This award from the Chemistry of Life Processes Program to Profesor Kathryn Splan of Macalester College supports research that investigates the interaction of copper ions with zinc-binding proteins. Many proteins require metal ions for proper function, and replacement of the usual metal ion with one exhibiting different chemical properties is likely to alter protein structure, and therefore, function. While metal-ion substitution has clear ramifications in the context of metal-ion toxicity, changes in protein function upon metal-ion substitution may also constitute a desirable functional strategy. The experiments reveal the susceptibility of zinc proteins toward substitution by copper and characterize the impact of this substitution on the protein's function. The project trains students in biochemical preparation and characterization techniques, thereby building solid technical skills in preparation for further study and/or entry into the work force. The results from the project also inform the fields of cell biology, neurochemistry, and neurobiology, particularly in those areas concerned with the molecular basis of diseases that are characterized by mis-regulated metal ion levels. In this work, the impact of Cu(I) on metalloprotein function is further investigated by characterizing the interaction of Cu(I) with the X-linked Inhibitor of Apoptosis Protein (XIAP), a Zn(II)-metalloprotein recently implicated in copper homeostasis. Multiple Zn(II) protein structural motifs have been shown to be susceptible to displacement by Cu(I), owing to the shared thiophilic character of both metal ions. Cu(I) substitution at the Zn(II) structural sites of XIAP is one possible mechanism by which XIAP function may be modulated by changing copper concentrations. A variety of spectroscopic and biochemical approaches are utilized to detect the displacement of zinc ions upon the addition of copper and the resulting structural and functional changes. Understanding Cu(I) interactions with this target at the molecular level deepens the understanding of metalloprotein susceptibility toward disruption by Cu(I) in general and clarifies the role of Cu(I) in XIAP function. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.