Colin S. Burns
Associate Professor, Biochemistry and Biophysics
Postdoctoral Researcher, UC Santa Cruz, 2000-2003
NIH Postdoctoral Researcher, UC Santa Cruz, 1998-2000
Ph.D., Chemistry, University of North Carolina at Chapel Hill, 1998
B.A., Kenyon College, 1993
Research in the Burns lab focuses on elucidating the metal binding motifs “natively unfolded” proteins use and on characterizing the effect metal binding has on the overall structure and behavior of the protein. Ultimately, the goal is to understand protein function, and possibly misfunction, on a molecular level. The structure and function of proteins is investigated using peptide synthesis, recombinant DNA methodology, and spectroscopy. We make extensive use of circular dichroism (CD) spectroscopy, fluorescence spectroscopy and mass spectrometry in these studies. Additionally, we make use of magnetic resonance techniques, specifically one and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. Many of proteins we plan to examine are involved in devastating neurological diseases.
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.
The Prion Protein
For the last several years we have been examining the mechanism of Cu2+ uptake by 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 and zinc homeostasis within the central nervous system. Using both CD and Metal-Catalyzed Oxidation Mass Spectrometry we have determined the number of binding modes used in the uptake of Cu2+ by the full metal binding-region. In accordance with previous work, we find evidence for coordination of Cu2+ by multiple histidine imidazoles at low PrP:Cu2+ ratios and there appear to be several possible isomers of this coordination mode.
Additionally, using fluorescence spectroscopy we have shown that Cu2+ and Zn2+ promote interactions between membrane-anchored peptides of the metal binding domain of the prion protein. With the structural information obtained from our studies, we can begin to critically evaluate hypotheses regarding the normal physiological function of PrP and the interplay between improper metal ion regulation and neurological disease.
Copper and zinc promoted PrP-PrP interactions.
Prothymosin-a 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 prothymosin-a’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. Prothymosin-a 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.
Using mass spectrometry and dialysis in conjunction with atomic absorption spectrometry we show that the central segment of this protein, corresponding to residues 51-89, can bind up to five Zn2+ ions with moderate affinity. We are currently studying the interesting anti-HIV properties of prothymosin-a-derived peptides.