Triple Quantum Decoherence under Multiple Refocusing: Slow Correlated Chemical Shift Modulations of C′ and N Nuclei in Proteins
Source: Journal of Biomolecular NMR, Volume 28, Number 3, March 2004 , pp. 263-272(10)
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 τc 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 HN belonging to a pair of consecutive amino acids. A cross-correlated relaxation rate RCS/CSC′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 α-helix, is shown to feature significant slow conformational exchange.
Document Type: Research Article
Affiliations: 1: Institute of molecular and biological chemistry, Swiss Federal Institute of Technology Lausanne (EPFL), CH 1015 Lausanne, Switzerland 2: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts MA 02115, U.S.A. 3: Department of chemistry, John Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, U.S.A. 4: Institute of molecular and biological chemistry, Swiss Federal Institute of Technology Lausanne (EPFL), CH 1015 Lausanne, Switzerland Département de chimie, associé au CNRS, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris cedex 05, France
Publication date: March 1, 2004