Mapping of the spectral density function of a C alpha-H alpha bond vector from NMR relaxation rates of a 13C-labelled alpha-carbon in motilin.
The peptide hormone motilin was synthesised with a 13C-enriched alpha-carbon in the leucine at position 10. In aqueous solution, six different relaxation rates were measured for the 13C alpha-H alpha fragment as a function of temperature and with and without the addition of 30% (v/v) of the cosolvent d2-1,1,1,3,3,3-hexafluoro-2-propanol (HFP). The relaxation rates were analysed employing the spectral density mapping technique introduced by Peng and Wagner [(1992) J. Magn. Reson., 98, 308-332] and using the model-free approach by Lipari and Szabo [(1982) J. Am. Chem. Soc., 104, 4546-4570]. The fit to various models of dynamics was also considered. Different procedures to evaluate the overall rotational correlation time were compared. A single exponential time correlation function was found to give a good fit to the measured spectral densities only for motilin in 30% (v/v) HFP at low temperatures, whereas at high temperatures in this solvent, and in D2O at all temperatures, none of the considered models gave an acceptable fit. A new empirical spectral density function was tested and found to accurately fit the experimental spectral density mapping points. The application of spectral density mapping based on NMR relaxation data for a specific 13C-1H vector is shown to be a highly useful method to study biomolecular dynamics. Advantages are high sensitivity, high precision and uniform sampling of the spectral density function over the frequency range.
Allard
P
P
Department of Biophysics, Arrhenius Laboratories, Stockholm University, Sweden.
Jarvet
J
J
Ehrenberg
A
A
Gräslund
A
A
D000595:Amino Acid Sequence; D000818:Animals; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009037:Motilin / Q000138:chemical synthesis / Q000737:chemistry* / Q000235:genetics; D012996:Solutions; D013552:Swine; D013696:Temperature; D013816:Thermodynamics
D002247:Carbon Isotopes; D012996:Solutions; D009037:Motilin