A Novel Model-Free Analysis of13C NMR Relaxation of Alanine-Methyl Side-Chain Motions in Peptides
✍ Scribed by Vladimir A. Daragan; Kevin H. Mayo
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 278 KB
- Volume
- 110
- Category
- Article
- ISSN
- 1064-1866
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✦ Synopsis
Amino-acid side chains probe details of protein internal sheet domain of platelet factor-4: IA*TLK (P5) and TAQLIA*TLK motions. NMR relaxation data on side chains, particularly NGRKICLDLQA (P20), were synthesized with 13 C enriched in methyl groups, contain information concerning motional C a and C b positions. 13 C NMR relaxation measurements (proton correlation times, restrictions, and correlations between varicoupled and decoupled) were performed at two NMR frequencies ous rotations (12-20). Methyl-group rotations are sensitive (150 and 62.5 MHz) and over a wide range of temperatures (5 to to protein/peptide conformation in terms of sequentially and 75ЊC) to study motional dynamics of the alanine side-chain methyl spatially neighboring residues (19, 20). Alanine presents the group and alanine side-chain-backbone motional correlations. simplest case to study side-chain motional dynamics and Cross-correlation spectral densities, J HCH (v C ), for C b H 3 in both side-chain-backbone motional correlations. Unrestricted ropeptides are positive, indicating methyl-group rotational anisottation of the alanine methyl group simplifies many rotational ropy. Various rotational models and model-free approaches have been used to analyze NMR relaxation data. The overall correlation correlation functions and reduces the number of model patimes show a stronger temperature dependence in P20 than in P5, rameters required to analyze NMR relaxation data.
In this indicating the influence on alanine motions of folded conformarespect, one has the opportunity to determine more accutional populations in P20. For analysis of alanine side-chain morately motional parameters from NMR experiments and to tions, an alternative model-free approach parameterized with a consider more realistic rotational models to explain the varinovel mixing parameter, A 2 , that depends on the ''geometry'' of ety of possible internal motions. C a -C b and C a -H bond rotations is proposed. By plotting the In this paper, motional dynamics of 13 C-enriched (C a , C b ) standard order parameter S 2 versus A 2 , motional models may alanine have been studied in two peptides derived from the be visually differentiated. Molecular dynamics calculations were b-sheet domain of platelet factor-4 (21): IA*TLK (P5) and performed to compare C a -C b and C a -H motions. Significant anti-TAQLIA*TLKNGRKICLDLQA (P20). The shorter pepcorrelated w(t) and c(t) backbone rotations can explain NMR tide P5 is part of the P20 sequence and permits us to study relaxation data for P20.