Can PISEMA experiments be used to extract structural parameters for mobile [beta]-barrels?

The effect of mobility on ^sup 15^N chemical shift/^sup 15^N-^sup 1^H dipolar coupling (PISEMA) solid state NMR experiments applied to macroscopically oriented β-barrels is assessed using molecular dynamics simulation data of the NalP autotransporter domain embedded in a DMPC bilayer. In agreement with previous findings for α-helices, the fast librational motion of the peptide planes is found to have a considerable effect on the calculated PISEMA spectra. In addition, the dependence of the chemical shift anisotropy (CSA) and dipolar coupling parameters on the calculated spectra is evaluated specifically for the β-barrel case. It is found that the precise choice of the value of the CSA parameters σ^sub 11^,σ^sub 22^ and σ^sub 33^ has only a minor effect, whereas the choice of the CSA parameter [theta] shifts the position of the peaks by up to 20 ppm and changes the overall shape of the spectrum significantly. As was found for α-helices, the choice of the NH bond distance has a large effect on the dipolar coupling constant used for the calculations. Overall, it is found that the alternating β-strands in the barrel occupy distinct regions of the PISEMA spectra, forming patterns which may prove useful in peak assignment.[PUBLICATION ABSTRACT]