Structure Determination of a Flexible Cyclic Peptide Based on NMR and MD Simulation 3J-Coupling

摘要

Molecular dynamics (MD) simulations, in which experimental values such as nuclear Overhauser effects (NOEs), dipolar couplings, ~3J-coupling constants or crystallographic structure factors are used to bias the values of specific molecular properties towards experimental ones, are often carried out to study the structure refinement of peptides and proteins. However, 3Jcoupling constants are usually not employed because of the multiplicity of torsional angle values (q) corresponding to each 3J-coupling constant value. Here, we apply the method of adaptively enforced restraining using a local-elevation (LE) biasing potential energy function in which a memory function penalizes conformations in case both the average < 3J> and the current 3J-values deviate from the experimental target value. Then, the molecule is forced to sample other parts of the conformational space, thereby being able to cross high energy barriers and to bring the simulated average <3J> close to the measured < 3J> value. Herein, we show the applicability of this method in structure refinement of a cyclo-β-- tetrapeptide by enforcing the 3J-value restraining with LE on twelve backbone torsional angles. The resulting structural ensemble satisfies the experimental 3J-coupling data better than the NMR model structure derived using conventional singlestructure refinement based on these data. Thus, application of local-elevation search MD simulation in combination with biasing towards 3J-coupling makes it possible to use ~3J-couplings quantitatively in structure determination of peptides.