View source for Paramagnetic Constraints in Structure Determination

== '''Introduction''' ==

The collection of paramagnetic constraint data and the use of those data as a part of a structure determination is fairly straight forward.&nbsp; RDCs can be collected using either the J-modulation or HSQC-TROSY methods described in the RDC section.&nbsp; Paramagnetic relaxation enhancements (PREs) are collected based on attenuation of signal intensity in HSQC or TROSY spectra.&nbsp; When Curie contributions from paramagnetic metals dominate it will be convenient to make measurements at multiple field strengths as the effects are field squared dependent and field variation provides a useful way to probe different distance ranges.&nbsp; We have access to spectrometers operating from 600 to 900 MHz.&nbsp; Pseudocontact shifts (PCSs) are measured by comparison of HSQC (or TROSY) cross-peak positions in diamagnetic (La<sup>3+</sup>) and paramagnetic complexes (Dy<sup>3+</sup> or Tb<sup>3+</sup>).&nbsp; Pairing of shifted and non-shifted peaks is facilitated by the fact that shifts in in both <sup>1</sup>H and <sup>15</sup>N dimensions are nearly equal on the ppm scale and are therefore connected by diagonal lines.&nbsp; Paramagnetic relaxation interferences (PRIs) produce differential effects on the α and β cross peaks of coupled HSQC spectra and the cross-correlation effects can be measured using experiments that we have developed for the measurement of correlation times from CSA/DD interference (Ref. 1).&nbsp; Integration of these data into structure characterization protocols is accomplished using programs such as XPLOR-NIH (Ref. 2) or REDCAT (Ref. 3)&nbsp; Routines for integration of PREs, RDCs, PCSs and PRI all exist, and use as a part of a structure determination protocol are relatively straightforward (Ref. 4).



== '''Protocols''' ==





== '''References''' ==

1.&nbsp;&nbsp; Liu, Y.Z., and Prestegard, J.H. (2008) Direct measurement of dipole-dipole/CSA cross-correlated relaxation by a constant-time experiment. ''J. Magn. Reson. 193'', 23-31.

2.&nbsp;&nbsp; Schwieters, C.D., Kuszewski, J.J., and Clore, G.M. (2006). Using Xplor-NIH for NMR molecular structure determination. ''Prog. NMR Spect. 48'', 47-62.

3.&nbsp;&nbsp; Valafar, H., and Prestegard, J.H. (2004) REDCAT: a residual dipolar coupling analysis tool. ''J. Magn. Reson. 167'', 228-241

4.&nbsp;&nbsp; Banci, L., Bertini, I., Cavallaro, G., Giachetti, A., Luchinat, C., and Parigi, G. (2004) Paramagnetism-based restraints for Xplor-NIH. ''J. Biomol. NMR&nbsp;28'', 249-261.