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Dan Neumann, National Institute of Standards and Technology, DMR 0944772

The role of electrostatic interactions in the local dynamics of biological and synthetic polyelectrolytes. Dan Neumann, National Institute of Standards and Technology, DMR 0944772.

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Dan Neumann, National Institute of Standards and Technology, DMR 0944772

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  1. The role of electrostatic interactions in the local dynamics of biological and synthetic polyelectrolytes Dan Neumann, National Institute of Standards and Technology, DMR 0944772 (a) The mean-squared displacement, <r2(T)> for unfolded and folded powder tRNA hydrated to 42% (w/w) with D2O (the first hydration layer). The dynamic transition (at ~200 K) and melting transition (at ~325 K) of secondary and tertiary interactions are indicated. (b) <r2(T)> for D2O solutions of unfolded and folded tRNA and unscreened and screened 83% sulfonated polystyrene (SPS). Å Å Å The local dynamics of RNA contribute to its biological functions including ligand recognition and catalysis. These motions are coupled to the local electrostatic and hydrodynamic environment as the folding of hydrated RNA is prompted by electrostatic neutralization of the negative charge on the backbone by Mg2+. Our quasielastic neutron scattering measurements, using the CHRNS-supported HFBS instrument, show that neutralization by Mg2+ increases the picosecond to nanosecond dynamics of hydrated tRNA while stabilizing its folded structure. The larger mean-squared displacement (<r2>) and smaller persistence length (lp, measured by SAXS) show that compact, folded tRNA is more flexible than when unfolded. This same result was observed for a sulfonated polystyrene (a synthetic polyectrolyte), indicating that the increased local dynamics originates from the charge screening of the polyelectrolyte rather than from sequence-specific interactions. These results are opposite to the relationship found between structural compactness and internal dynamics for proteins where the folded state is more rigid than the unfolded state. The pair distance distribution functions, P(r), obtained from SAXS. The radius of gyration, Rg, and persistence length, lp, were estimated from P(r). Black lines are the fit of P(r) to the exponential equation at r > Rg on the basis of a worm-like chain model. NIST 70NANB7H6177 and NSF DMR-0944772 Joon Ho Roh, MadhuTyagi, R. M. Briber, Sarah A. Woodson, Alexei P. Sokolov, JACS. 133, 16406 (2011).

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