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An NMR Confirmation for Increased Folded State Entropy Following Loop Truncation
journal contribution
posted on 2018-11-09, 00:00 authored by Yulian Gavrilov, Shlomi Dagan, Ziv Reich, Tali Scherf, Yaakov LevyPrevious
studies conducted on flexible loop regions in proteins
revealed that the energetic consequences of changing loop length predominantly
arise from the entropic cost of ordering a loop during folding. However,
in an earlier study of human acylphosphatase (hmAcP) using experimental
and computational approaches, we showed that thermodynamic stabilization
upon loop truncation can be attributed mainly to the increased entropy
of the folded state. Here, using 15N NMR spectroscopy,
we studied the effect of loop truncation on hmAcP backbone dynamics
on the picosecond–nanosecond timescale with the aim of confirming
the effect of folded state entropy on protein stability. NMR-relaxation-derived
N–H squared generalized order parameters reveal that loop truncation
results in a significant increase in protein conformational flexibility.
Comparison of these results with previously acquired all-atom molecular
dynamics simulation, analyzed here in terms of squared generalized
NMR order parameters, demonstrates general agreement between the two
methods. The NMR study not only provides direct evidence for the enhanced
conformational entropy of the folded state of hmAcP upon loop truncation
but also gives a quantitative measure of the observed effects.