title: Measurement of proton chemical shifts in invisible states of slowly exchanging protein systems by chemical exchange saturation transfer.
abstract: Chemical exchange saturation transfer (CEST) NMR spectroscopy has emerged as a powerful technique for studies of transiently formed, sparsely populated (excited) conformational states of protein molecules in slow exchange with a dominant structure. The most popular form of the experiment, and the version originally developed, uses a weak (1)H radio frequency field to perturb longitudinal magnetization of one state with the effect transferred to magnetization in the second conformation via chemical exchange. A significant limitation of the method for protein applications emerges from (1)H magnetization transfer via dipolar relaxation (NOE effect) that can severely complicate analysis of the resulting CEST profile. This is particularly an issue since the (1)H chemical shifts of the excited state, critical for structural studies of these elusive conformers, become difficult to extract. Here we present a method for measurement of these shifts via CEST experiments in which the NOE effect is not an issue. The methodology is illustrated through applications to a pair of exchanging systems where the results are cross-validated.
authors.affiliation: Departments of Molecular Genetics, Biochemistry and Chemistry, The University of Toronto, Toronto, Ontario, Canada, M5S 1A8. guillaume@pound.med.utoronto.ca
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bouvignies
authors.forename: Lewis E
authors.initials: LE
authors.lastname: Kay
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D011506:Proteins / Q000737:chemistry*; D011522:Protons; D012015:Reference Standards
chemical_list: D011506:Proteins; D011522:Protons