Simple tests for the validation of multiple field spin relaxation data
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15N spin relaxation data is widely used to extract detailed dynamic information regarding bond vectors such as the amide N–H bond of the protein backbone. Analysis is typically carried using the Lipari–Szabo model-free approach. Even though the original model-free equation can be determined from single field R 1, R 2 and NOE, over-determination of more complex motional models is dependent on the recording of multiple field datasets. This is especially important for the characterization of conformational exchange which affects R 2 in a field dependent manner. However, severe artifacts can be introduced if inconsistencies arise between experimental setups with different magnets (or samples). Here, we propose the use of simple tests as validation tools for the assessment of consistency between different datasets recorded at multiple magnetic fields. Synthetic data are used to show the effects of inconsistencies on the proposed tests. Moreover, an analysis of data currently deposited in the BMRB is performed. Finally, two cases from our laboratory are presented. These tests are implemented in the open-source program relax, and we propose their use as a routine check-up for assessment of multiple field dataset consistency prior to any analysis such as model-free calculations. We believe this will aid in the extraction of higher quality dynamics information from 15N spin relaxation data.
KeywordsConsistency test Model-free analysis Spin relaxation Protein dynamics relax program
We would like to thank Chris MacRaild for conversations at the beginning of this work, Edward d’Auvergne for encouraging us to implement these simple tests into relax, Lukáš Žídek for enthusiastic comments on this work, and Pierre-Yves Savard for critical reading of this manuscript. This work was supported by operating grants from FQRNT (Québec) and NSERC (Canada), infrastructure grants from CFI (Canada) and studentships to S. Morin from NSERC (Canada), FRSQ (Québec) and Fondation J. Arthur Vincent.
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