Spectral-Density Mapping of13Cα–1HαVector Dynamics Using Dipolar Relaxation Rates Measured at Several Magnetic Fields

✍ Scribed by Jüri Jarvet; Peter Allard; Anders Ehrenberg; Astrid Gräslund

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 164 KB
• Volume: 111
• Category: Article
• ISSN: 1064-1866
• DOI: 10.1006/jmrb.1996.0056

✦ Synopsis

The spectral-density mapping of a 13 C a -1 H a vector of Leu 10 in mension to the relaxation data, although the information the 22-residue peptide hormone motilin [P. Allard, J. Jarvet, A. content of the six relaxation rates in the time domain is Ehrenberg, and A. Gra ¨slund, J. Biomol. NMR 5, 133-146 (1995)] the same as for the spectral-density values in the frequency is extended in this paper to three polarizing fields 9.4, 11.7, and domain. The correspondence between the two representa-14.1 T in order to improve the accuracy of the calculated spectraltions is somewhat analogous to the relation between the freedensity function J(v) and to extend the sampling range up to induction decay and the spectrum in NMR spectroscopy. 750 MHz. The problem with a usually large relative error in J( v H )

When experiments are done at different magnetic fields, one is eliminated since the generally more precise J(v H 0 v C ) and can calculate the slope of the spectral-density function at J(v H / v C ) determined at other fields appear at nearly the same different sampling frequencies. The slope of the spectralfrequencies. The fitting of dynamic models to the points of spectral density was made with error weighting, and the influence of J( v H ) density function at different frequencies is very useful when was found to be negligible. Therefore, the high-frequency part comparison is made between experimental data and dynamiof the spectral-density function is determined essentially without cal models.

influence from the two transverse-type relaxation rates. In the case With the spectral-density mapping technique, the meaof a carbon-proton vector, the relaxation is mainly determined surement of the spectral-density function is separated from by dipolar interaction and is only weakly influenced by other relaxthe fitting of dynamic models, which is not true, e.g., when ation mechanisms, which makes it particularly suitable for the using the model-free approach of Lipari and Szabo (2, 3).

spectral-density mapping technique. The measured relaxation

To obtain spectral-density values, which can discriminate rates in the time domain are transformed into the frequency dobetween different motional models, the precision of experimain by spectral-density mapping, and the slopes in different frequency regions are important parameters when comparing experi-mental relaxation rates must be high. Less-accurate data are mental data with theoretical models of motion. Using an adjustable generally used as input for the model-free analysis (2, 3) internuclear distance r eff , combined with the model-free approach, which still leads to reasonable values for the overall rotait is possible to obtain a reasonable fit to measured spectral-density tional correlation time t m and for the general order parameter points at J(0) and around J( v C ). At the same time, however, the S. For peptides as well as for proteins, the correlation time high-frequency slope of the spectral-density function defined by for overall rotational motion is typically on the order of J(v H 0 v C ) and J( v H / v C ) could not be reproduced. ᭧ 1996 nanoseconds, and, as a consequence, the numerical values Academic Press, Inc.

of different spectral-density points differ in size by at least an order of magnitude at the magnetic fields used here.

When the model-free approach was introduced (2, 3), the * To whom correspondence should be addressed.