Improved Estimation of Protein Rotational Correlation Times fromN Relaxation Measurements |
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Authors: | Shenggen Yao Mark G Hinds Raymond S Norton |
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Institution: | Biomolecular Research Institute, 343 Royal Parade, Parkville, Victoria, 3052, Australia |
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Abstract: | In the study of protein backbone dynamics by15N relaxation measurements, an initial estimation of the isotropic global correlation time, τm, is usually obtained from the averageT1/T2ratio of nuclear spins that do not exhibit slow internal motion and withT2values not significantly shortened by chemical or conformational exchange processes. Different methods have been used for identification of the rates of internal motion. However, the number of nuclear spins included in the τmestimation is often larger than the number that ultimately can be fitted to a single-order parameter,S2, implying that some nuclear spins involved in the initial τmestimation actually have an effective internal correlation time, τe, not as fast as assumed. As a consequence, τmis underestimated, since internal motion reduces theT1/T2ratio. This situation becomes more obvious if the molecule has a large τmvalue because the reduction inT1/T2ratio arising from internal motion is more significant than for molecules with smaller τmand the same degree of internal motion. This Communication describes a more reliable method for identifying nuclear spins which should be excluded from the τmestimation because of insufficiently rapid internal motion. This results in an improved τmvalue, giving a much better agreement between the number of nuclear spins fitted successfully to a single-order parameter,S2, and those used in the τmestimation. |
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Keywords: | 15N relaxation measurements global correlation time protein dynamics rate of internal motion NOE |
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