Dataset Information

Structure and disorder in the ribonuclease S-peptide probed by NMR residual dipolar couplings.

ABSTRACT: NMR residual dipolar couplings for the S-peptide of ribonuclease A aligned in C8E5/n-octanol liquid crystals are consistent with the presence of a native-like alpha-helix structure undergoing dynamic fraying. Residues 3-13, which correspond to the first alpha-helix of ribonuclease A, show couplings that become more negative at low temperature and in the presence of salt, conditions which stabilize alpha-helical structure in the S-peptide. By contrast, dipolar couplings from the N and C termini of the peptide are close to zero and remain nearly invariant with changes in solution conditions. Torsion angle dynamics simulations using a gradient of dihedral restraint bounds that increase from the center to the ends of the peptide reproduce the experimentally observed sequence dependence of dipolar couplings. The magnitudes of residual dipolar couplings depend on the anisotropy of the solute. Native proteins often achieve nearly spherical shapes due to the hydrophobic effect. Embryonic partially folded structures such as the S-peptide alpha-helix have an intrinsically greater potential for anisotropy that can result in sizable residual dipolar couplings in the absence of long-range structure.

SUBMITTER: Alexandrescu AT

PROVIDER: S-EPMC2366913 | biostudies-literature | 2003 Oct

REPOSITORIES: biostudies-literature

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Structure and disorder in the ribonuclease S-peptide probed by NMR residual dipolar couplings.

Alexandrescu Andrei T AT Kammerer Richard A RA

Protein science : a publication of the Protein Society 20031001 10

NMR residual dipolar couplings for the S-peptide of ribonuclease A aligned in C8E5/n-octanol liquid crystals are consistent with the presence of a native-like alpha-helix structure undergoing dynamic fraying. Residues 3-13, which correspond to the first alpha-helix of ribonuclease A, show couplings that become more negative at low temperature and in the presence of salt, conditions which stabilize alpha-helical structure in the S-peptide. By contrast, dipolar couplings from the N and C termini o ...[more]

PMID: 14500871

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Project description:The solution conformation behavior of a dermatan-derived tetrasaccharide--Delta HexA-(1-->3)-GalNAc4S-beta-(1-->4)-IdoA-alpha-(1-->3)-red-GalNAc4S (S is a sulfate group)--has been explored by means of NMR spectroscopy, especially by NOE-based conformational analysis. The tetrasaccharide was present as four species, two of which are chemically different in the anomeric orientation of the reducing 2-deoxy-2-acetamido-galactose (red-GalNAc) residue, while the other two are the result of different conformations of the iduronic acid (IdoA) unit. The two alpha-beta-interconverting anomers were present in a 0.6:1 ratio. Ring conformations have been defined by analysis of (3)J(H,H) coupling constants and interresidual NOE contacts. Both 2-deoxy-2-acetamido-galactose (GalNAc) residues were found in the (4)C(1) chair conformation, the unsaturated uronic acid (Delta-Hex A) adopts a strongly predominant half-chair (1)H(2) conformation, while the IdoA residue exists either in the (1)C(4) chair or in the (2)S(0) skewed boat geometries, in a 4:1 ratio. There is a moderate flexibility of Phi and Psi torsions as suggested by nuclear Overhauser effects (NOEs), molecular modeling (MM), and molecular dynamics (MD) studies. This was further investigated by residual dipolar couplings (RDCs). One-bond C--H RDCs ((1)D(C,H)) and long-range H-H ((3)D(H,H)) RDCs were measured for the tetrasaccharide in a phage solution and interpreted in combination with restrained MD simulation. The RDC-derived data substantially confirmed the validity of the conformer distribution resulting from the NOE-derived simulations, but allowed an improved definition of the conformational behavior of the oligosaccharides in solution. In summary, the data show a moderate flexibility of the four tetrasaccharide species at the central glycosidic linkage. Differences in the shapes of species with the IdoA in skew and in chair conformations and in the distribution of the sulfate groups have also been highlighted.

Dataset Information

Structure and disorder in the ribonuclease S-peptide probed by NMR residual dipolar couplings.

Publications

Structure and disorder in the ribonuclease S-peptide probed by NMR residual dipolar couplings.

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