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<div><font face="Arial" size="+1" color="#000000">Seminar on<br>
<b>Modern Optics and Spectroscopy<br>
<br>
Joel Parks</b>,<br>
Rowland Institute at Harvard<br>
<br>
<i><b>Probing the dynamics of trapped gas-phase proteins with
photons<br>
<br>
</b></i>December 6, 2005<br>
12:00 - 1:00 p.m.</font></div>
<div><font face="Arial" size="+1" color="#000000">34-401<br>
<br>
</font><font face="New York" size="+1" color="#000000">Abstract:<br>
<br>
</font><font face="Times New Roman" size="+1"
color="#000000">Characterization of the structure and dynamics of
biopolymers is of paramount importance to understanding life processes
at the molecular level. Measurements of these molecules in the absence
of a solvent or surface are useful for elucidating the effects of the
solvent environment on the native structure and dynamics. We have been
applying fluorescence spectroscopy to unsolvated biomolecule ions to
take advantage of the unique ability of this technique to directly
probe the local molecular environment surrounding the fluorophore.
This talk will discuss the first fluorescence measurements of protein
unfolding in the gas phase. Trp-cage is an actively studied 20 amino
acid protein that folds cooperatively in 4</font><font face="Symbol"
size="+1" color="#000000"> m</font><font face="Times New Roman"
size="+1" color="#000000">s and presents a tractable size for
calculations. The native structure includes a Tryptophan amino acid
"caged" by three Proline amino acids, a feature that makes this
protein especially suitable for the detection of unfolding in the gas
phase by intramolecular fluorescence quenching. As the protein is
heated to induce conformational change, the Trp will be released from
its cage and become more exposed to intramolecular collisions with a
covalently attached fluorescent dye, BODIPY TMR. Such collisions
quench the dye fluorescence so that conformational changes will be
directly correlated with the fluorescence intensity. The talk will
describe these new methods and present results of their application to
Trp-cage, and polypeptides.</font></div>
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