Research
Proteins are responsible for catalyzing nearly all the necessary chemical reactions in biological systems.  Often, they require metal ion cofactors to function properly, yet how proteins coordinate and control the reactivity of these species is a matter of intense research interest.  Knowledge of metalloprotein structure is essential for developing concepts related to metal ion uptake and release, metal reactivity, protein-protein interactions, and regulatory processes.  Hence, structural determination is essential for understanding the function of these biomolecules on a fundamental level.  This is especially true if we wish to establish a basis for rational therapeutic intervention in disease pathways.

The proteins I am most interested in are either unfolded or adopt non-globular structures under physiological conditions.  Proteins such as these are referred to as “natively unfolded.”  Many proteins belonging to this class coordinate metal ions.  This raises two important questions:  What types of metal binding motifs do natively unfolded proteins have?  And do they differ significantly from those of folded proteins?  Interestingly, a number of these proteins are implicated in disease, including Alzheimer’s disease, Parkinson’s disease, and Mad Cow’s disease.  Recent research suggests there may be a link between metal homeostasis and disease.

For the last several years I have been examining Cu²⁺ binding in the prion protein (PrP).  PrP is responsible for a class of fatal neurological diseases called transmissible spongiform encephalopathies (TSE’s).  Recent studies suggest that PrP is involved with copper homeostasis within the central nervous system.  The majority of copper binding takes place in a domain composed of repeating PHGGGWGQ sequences, where the underlined residues directly coordinate Cu²⁺.  In collaboration with other researchers, we have identified the structure of the major Cu²⁺ binding site in PrP (shown below).

New Directions
Two proteins I have selected as targets for study are prothymosin-a (ProTa) and a-synuclein (a-syn).  ProTa is a natively unfolded, nuclear protein consisting of 110 amino acids.  The precise function is unknown, however evidence suggests it is associated with cell proliferation.  Because ProTa’s high level of expression in a wide variety of cell types and tissues and the fact that it has a high level of evolutionary conservation all the way from yeast to humans one would expect it to play an essential role in organisms.  ProTa appears to specifically interact with Zn²⁺ and undergoes considerable rearrangement when exposed to this metal ion.  This interaction may very well be important for the function of this protein.  An approach using model peptide complexes in conjunction with NMR spectroscopy will allow us to probe the structure of the protein-Zn²⁺ complex and will provide a basis for inferring what function the protein performs and how it does it.

a-Synuclein belongs to the family of natively unfolded proteins and is abundant in various regions of the brain.  The normal function of a-syn is unknown, but deposition of a-syn aggregates is a pathological hallmark of Parkinson’s disease.  It has been demonstrated that a-syn interacts with Cu²⁺ and that this metal ion greatly increases the rate of aggregation.  The nature and structure of the a-syn-Cu²⁺ interaction will be elucidated using peptide design, recombinant DNA methodology, and EPR spectroscopy.