title: Triple quantum decoherence under multiple refocusing: slow correlated chemical shift modulations of C' and N nuclei in proteins.
abstract: A new experiment allows the identification of residues that feature slow conformational exchange in macromolecules. Rotations about dihedral angles that are slower than the global correlation time tau(c) cause a modulation of the isotropic chemical shifts of the nuclei. If these fluctuations are correlated they induce a differential line broadening between three-spin single-quantum and triple-quantum coherences involving three nuclei such as the carbonyl C', the neighbouring amide nitrogen N and the amide proton H(N) belonging to a pair of consecutive amino acids. A cross-correlated relaxation rate R (CS/CS)(C'N) can be determined that corresponds to the sum of the isotropic and anisotropic contributions to the chemical shift modulations of the carbonyl carbon and nitrogen nuclei. Only the isotropic contributions depend on the pulse repetition rate of a multiple-refocusing sequence. An attenuation of the relaxation rate with increasing pulse repetition rate can therefore be attributed to slow motions. The asparagine N25 residue of ubiquitin, located in the first alpha-helix, is shown to feature significant slow conformational exchange.
authors.affiliation: Institute of molecular and biological chemistry, Swiss Federal Institute of Technology Lausanne (EPFL), CH 1015 Lausanne, Switzerland.
authors.forename: Julien
authors.initials: J
authors.lastname: Wist
authors.forename: Dominique
authors.initials: D
authors.lastname: Frueh
authors.forename: Joel R
authors.initials: JR
authors.lastname: Tolman
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Bodenhausen
mesh_terms: D000465:Algorithms; D001216:Asparagine / Q000737:chemistry; D002244:Carbon / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D011789:Quantum Theory; D014452:Ubiquitins / Q000737:chemistry
chemical_list: D011506:Proteins; D014452:Ubiquitins; D001216:Asparagine; D002244:Carbon; D009584:Nitrogen