Changes

http://thread.gmane.org/gmane.science.nmr.relax.user/1552

'''Is possible to use relax to perform a model-free analysis using only relaxation data collected at a single magnetic field strength?'''

If you play with the optimisation settings you can even find identical results to within machine precision - relax can mimic these other softwares.

The key is that the full analysis protocol is rather complicated - many people don't understand this - and that these softwares do not implement the full iterative protocol. Therefore one either have to perform it manually or write a script to perform all of the steps.

This is a rather large script located at '''auto_anlayses/dauvergne_protocol.py'''. This protocol is used by the GUI. So one option would be to copy this '''auto_anlayses/dauvergne_protocol.py''' script and modify it for the figure 7.2 protocol.

I must warn you about using single field strength data. It is now quite difficult to publish a model-free analysis with only single field strength data as most of the field know about the catastrophic analysis failures resulting in large amounts of artificial motion. These failures can also be much more subtle. Many reviewers will ask for such data to be collected as the results cannot not be trusted otherwise. For a model-free analysis, it is almost

essential to collect data at multiple field strengths, otherwise it can be sometimes impossible to distinguish between the anisotropic part of the Brownian tumbling of the molecule and internal motion - specifically due to the NH vectors in secondary structure elements all pointing in a similar direction. I have a much better explanation, as well as citations to all the relevant literature in [d'Auvergne and Gooley, 2007]. In this paper, you will see reviewed both the artificial nanosecond motions of the [Schurr et al., 1994] paper and the artifical R_ex motions of the [Tjandra et al., 1995] paper.

Finally, you will probably find it much easier to spend the 7-8 days collecting data at another field strength than to implement the [[#Protocol|protocol]] in a relax, Modelfree4, or Dasha script (or via multiple iterations of the GUI programs), as well as study all of the relevant literature to understand all of the types of failures than only occurs with single field strength data. With multiple field strength data you can perform [https://gna.org/users/semor Sebastien Morin's] consistency testing analysis in relax[Morin and Gagné, 2009] (see http://www.nmr-relax.com/manual/Consistency_testing.html). That way you can see if your per-experiment temperature calibration and

per-experiment temperature control techniques have works sufficiently well (http://www.nmr-relax.com/manual/Temperature_control_calibration.html) and if you have used long enough recycle delays. Collecting data at a second field would probably save you significant amounts of time, and has the additional benefit that it would guarantee that the dynamics you see at the end will be real. I cannot emphasize enough how important it is to collect data at multiple fields, most importantly the NOE and R₂ data.

*[*Clore et al., 1990] Clore, G. M., Szabo, A., Bax, A., Kay, L. E., Driscoll, P. C., and Gronenborn, A. M. (1990). Deviations from the simple 2-parameter model-free approach to the interpretation of N-15 nuclear magnetic-relaxation of proteins. ''J. Am. Chem. Soc.'', '''112'''(12), 4989-4991. (DOI [http://dx.doi.org/10.1021/ja00168a070 10.1021/ja00168a070]).