Ann Rich PhD

June 2002

In search of the unsuspected

Ask Anne Rich what she finds most exciting about her work as a post-doctorate researcher in Dartmouth's Chemistry Department and she quickly answers, “Easy. Isothermal Titration Calorimetry.” That is, when this precise and sensitive technique goes well. “It’s exciting to get something new that’s unexpected.” Especially if it contradicts what the experts believe.

Anne Rich, who has been interested in chemistry since high school, studies the way metals interact with proteins —an interaction that plays a critical role in living organisms. After moving to Hanover from Sydney, Australia in 2001, she now does research with Dartmouth chemist Dean Wilcox on zinc fingers, DNA binding proteins that control when genes turn on and turn off. “Zinc fingers” might conjure up the thought of the Tin Man from the Wizard of Oz. In fact zinc fingers do resemble fingers on a molecular scale. Proteins often hold very specific shapes, corresponding to the job they perform within a cell. Certain gene regulatory proteins in the cell nucleus have finger-like areas called zinc fingers that grab onto the DNA strand’s binding site. In the center of each “finger” is a zinc ion that dictates the shape, or conformation, of the protein, allowing it to behave much like a key fitting into a lock. A wrong ion, or an extra ion of a different sort can change the way the protein is shaped and keep it from fitting the lock, or the specific area of the DNA strand it is supposed to grab onto. So, why are these gene regulatory proteins binding to DNA? These proteins serve as initiators in the process of gene expression. It is these proteins, that attach to specific sites near a gene, that switch on the chain reaction beginning with translating a gene on a segment of DNA to building a protein that will be used by the body for any purpose—from digesting lactose to healing a sunburn. So why does that matter to a chemist?

Anne is looking at the effects that other metals could have if they are incorporated into the gene regulatory protein instead of, or along with, the zinc ion. Specifically, she looks at how toxic pollutants cadmium, lead, and arsenic bind to the gene regulatory protein when they are present in the cell. The implications of this can be big. Disrupting the formation of the zinc fingers can disrupt DNA binding, transcription, and ultimately the production of proteins that are necessary for almost every aspect of the body’s systems. Arsenic is also a co-carcinogen, meaning that if it becomes incorporated into the body, it can act in concert with other factors such as UV light exposure to cause cancer. So the function of this little zinc ion has big importance.

And this is where isothermal titration calorimetry comes in. This super-sensitive instrument measures the minute amounts of heat generated or absorbed when two molecules interact—in the case of Anne’s research, the interactions of zinc finger molecules with other molecules. The ITC technique is used to study these interactions to better understand how zinc fingers bind to DNA, for example, how many binding sites zinc fingers have. Then scientists will be able to better understand the consequences of exposure to toxic metals such as arsenic that may disrupt proper binding. The ITC instrument is so sensitive that it even picks up air currents. All work on it must be done in airtight and temperature controlled conditions. Otherwise the smallest outside influences can destroy the data.

This is why Anne likes it so much. It takes a lot of effort and patience to make sure everything is set up properly, and when it is, the results are satisfying. Anne’s research may contribute to new knowledge surrounding toxic metals which turns a tedious-sounding technique into an essential tool for dealing with toxic metal pollution and the health problems associated with it. And that’s exciting.

Bethany Fleishman
CEHS intern

Publications during training:

Nugent JHA, Rich AM, Evans MCW. 2001. Photosynthetic Water Oxidation: Towards a Mechanism. Biochim. Biophys. Acta, 1503, 138-146.

Rich AM, Kruszyna HG, and Wilcox DE. Thermodynamic comparison of arsenite and monomethylarsinite binding to a simple dithiol ligand: implications for As+3 toxicity. Manuscript in preparation 2003.

Rich AM, Schenk AD, Bombarda E, Keiffer E, and Wilcox DE. Thermodynamics of Zn+2 binding to a classical C2H2 zinc finger and a non-classical C4 binding site. Manuscript in preparation 2003.

Weder JE, Hambley TW, Kennedy BJ, Lay PA, Foran GJ, Rich AM. 2001. Determination of the structures of anti-inflammatory Copper(II) Dimers of Indomethacin by Multiple-Scattering Analyses of XAFS Data. Inorg. Chem, 40, 1295-1302.

Awards and Presentations:

2001 - Poster presentation, “Toxic metal interactions with zinc finger,” 2001 Superfund Basic Research Program Annual Meeting--Assessing Risks of Hormonally Active Agents, Gainesville, FL. Included travel award.

2001 - Poster presentation, “Toxic Metal Interactions with Zinc Fingers,” 10th International Conference on Bioinorganic Chemistry, Florence, Italy. Included travel award.

2002 - Honorary Member, Sigma-Xi, The Chemical Society.

2002 - Poster presentation, “Toxic Metal Interactions with Zinc Fingers,” 224th National Meeting, American Chemical Society, Boston, MA.

2002 - Poster presentation, “Isothermal Titration Calorimetry Measurements of Zinc Binding to Transcription Factors: Relevance to Metal Toxicity,” Inaugural