Peptide Internal Motions on Nanosecond Time Scale Derived from Direct Fitting of 13C and 15N NMR Spectral Density Functions
✍ Scribed by Kevin H Mayo; Vladimir A Daragan; Djaudat Idiyatullin; Irina Nesmelova
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 107 KB
- Volume
- 146
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
NMR relaxation-derived spectral densities provide information on molecular and internal motions occurring on the picosecond to nanosecond time scales. Using 13 C and 15 N NMR relaxation parameters [T 1 , T 2 , and NOE] acquired at four Larmor frequencies (for 13 C: 62.5, 125, 150, and 200 MHz), spectral densities J(0), J( C ), J( H ), J( H ؉ C ), J( H ؊ C ), J( N ), J( H ؉ N ), and J( H ؊ N ) were derived as a function of frequency for 15 NH, 13 C ␣ H, and 13 C  H 3 groups of an alanine residue in an ␣-helixforming peptide. This extensive relaxation data set has allowed derivation of highly defined 13 C and 15 N spectral density maps. Using Monte Carlo minimization, these maps were fit to a spectral density function of three Lorentzian terms having six motional parameters: 0 , 1 , 2 , c 0 , c 1 , and c 2 , where 0 , 1 and 2 are correlation times for overall tumbling and for slower and faster internal motions, and c 0 , c 1 , and c 2 are their weighting coefficients. Analysis of the high-frequency portion of these maps was particularly informative, especially when deriving motional parameters of the side-chain methyl group for which the order parameter is very small and overall tumbling motions do not dominate the spectral density function. Overall correlation times, 0 , are found to be in nanosecond range, consistent with values determined using the Lipari-Szabo model-free approach. Internal motional correlation times range from picoseconds for methyl group rotation to nanoseconds for backbone N-H, C ␣ -H, and C ␣ -C  bond motions. General application of this approach will allow greater insight into the internal motions in peptides and proteins.