Abstract
Adiabatically swept pulses were originally designed for the purpose of broadband spin inversion. Later, unexpected advantages of their utilization were also found in other applications, such as refocusing to excite spin echoes, studies of chemical exchange or fragment-based drug design. Here, we present new experiments to characterize fast (ps–ns) protein dynamics, which benefit from little-known properties of adiabatic pulses. We developed a strategy for measuring cross-correlated cross-relaxation (CCCR) rates during adiabatic pulses. This experiment provides a linear combination of longitudinal and transverse CCCR rates, which is offset-independent across a typical amide ^{15}hbox {N} spectrum. The pulse sequence can be recast to provide accurate transverse CCCR rates weighted by the populations of exchanging states. Sensitivity can be improved in systems in slow exchange. Finally, the experiments can be easily modified to yield residue-specific correlation times. The average correlation time of motions can be determined with a single experiment while at least two different experiments had to be recorded until now.Electronic supplementary materialThe online version of this article (doi:10.1007/s10858-015-9994-8) contains supplementary material, which is available to authorized users.
Highlights
Protein dynamics are essential for most biological processes
We developed a strategy for measuring cross-correlated crossrelaxation (CCCR) rates during adiabatic pulses
According to semi-classical NMR relaxation theory (Wangsness and Bloch 1953; Redfield 1965) all relaxation rates are determined by linear combinations of discrete values of the spectral density function JðxÞ which describes the probability of finding motions at a given
Summary
Protein dynamics are essential for most biological processes. The possibility of studying dynamics on various timescales at atomic resolution makes the analysis of NMR relaxation rates unique among other biophysical methods. Robust symmetrical reconversion methods allow accurate measurement of transverse CCCR rates (Pelupessy et al 2003), but the precision is significantly reduced in the presence of slow exchange when the precession frequency changes during the exchange process. We introduce variants of experiments that can directly provide values of the spectral density function at zero frequency J(0). These J(0) values provide interesting information about the timescales of the dominant motion in the ps-ns range. Symmetrical reconversion experiments (Pelupessy et al 2003, 2007) were used to measure the transverse (gxy) and longitudinal (gz) cross-relaxation rates due to cross-correlated fluctuations of the 15N chemical shielding anisotropy (CSA) and the 15N–1H dipole–dipole interaction in ubiquitin.
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