Off-resonance effects in 15N T2 CPMG measurements |
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Authors: | Dmitry M Korzhnev Eugene V Tischenko Alexander S Arseniev |
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Institution: | (1) Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Ul. Miklukho-Maklaya 16/10, Moscow, 117871, Russia |
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Abstract: | The systematic difference between T
2 values obtained from CPMG and T
1 experiments was observed for backbone 15N nuclei of bacterial ribonuclease barnase. Theoretical consideration suggests that the observed difference is caused by off-resonance effects of 180° pulses of the CPMG pulse train. Namely, at off-resonance conditions T
1-dependent secondary echo coherence pathways considerably contribute to the signal decay in the CPMG experiment and result in systematic (up to 10%) offset-dependent overestimation of 15N T
2 measured by the CPMG technique. Under certain circumstances off-resonance effects result in dependence of 15N T
2 on CPMG frequency, which might be erroneously interpreted as conformational exchange on the millisecond time-scale. A procedure for numerical correction of 15N T
2 (CPMG) data is proposed. |
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Keywords: | backbone dynamics conformational exchange proteins relaxation |
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