Please join us for ………………
Andrea Markelz
University of Buffalo, SUNY
WEDNESDAY, June 15, 13:30 (EDT)
"Uncovering Protein Structural Dynamics with Terahertz Light"
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Abstract:
The long-range structural vibrations of biomacromolecules (molecular weight >
5kDa), are matched to biological thermal energies. This intriguing overlap
raises the question if, like sequence and structure, these dynamics are also
evolutionarily optimized for robust and efficient biochemistry. The vibrations
for such massive systems are necessarily complex. The structural vibrations
involve displacements of entire subdomains, are numerous and closely spaced in
energy, leading to dense spectra. The spectra are further complicated by the
energy overlap with collective excitations of the biological water necessary
for in vivo structure and biological relevance. Compounded with these effects,
while a single spectrum corresponds to a single structure, biomacromolecular
structure thermally samples small configurational changes in time, leading to
variation in the vibrational spectra. These effects all lead to the smooth
featureless spectra seen by investigators for macroscopic samples. In this talk
I will provide an overview of terahertz biomolecular studies and discuss the
fundamental issue of isolating vibrational excitations based on specific
structural displacements. An example of a technique to provides this isolation
is anisotropic terahertz microspectroscopy (ATM). Using ATM we have found that
indeed there are biases in the directionality of vibrational displacements
which change with ligand binding and photoexcitation. In particular
photoexcitation measurements of orange carotenoid protein (OCP) demonstrate
that intermediate states of the photo cycle coincide with changes in the
directionality of vibrations, suggesting these reorganizations of the dynamics
may assist with access to intermediate state structures. Finally, I will
discuss the challenges of current instrumentation, computational tools and
sample preparation that need to be addressed to more fully realize the
potential of THz in the understanding of the role of picosecond structural
dynamics in biology.
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