Practical aspects of 15N CPMG transverse relaxation experiments for proteins in solution

Abstract

AbstractThe 15N transverse relaxation as measured by the Carr‐Purcell‐Meiboom‐Gill (CPMG) sequence is often used to characterize protein backbone dynamics in solution. In the 15N CPMG experiment, the delay between 15N CPMG pulses typically is set sufficiently short to minimize the effects of relaxation by the 15N‐1H antiphase component. This limits the total relaxation duration of the CPMG experiment because frequent application of the high B1 field to the heteronucleus may cause probe damage. The resulting antiphase component can be minimized by using 1H composite decoupling or by applying 1H 180° pulses more frequently than the 15N CPMG pulses. In this study, we simulated 15N CPMG relaxation in the presence of either 1H composite decoupling or 1H 180° pulses and compared the results with the experimental transverse relaxation data acquired with [u‐15N]‐ or [u‐15N, u‐2H]‐ubiquitin samples. We explain systematic errors resulting from these CPMG experiments and describe a method for recording 15N transverse relaxation in a manner that minimizes probe problems. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 63–75, 2009.