title: Paramagnetic doping of a 7TM membrane protein in lipid bilayers by Gd³⁺-complexes for solid-state NMR spectroscopy.
abstract: A considerable limitation of NMR spectroscopy is its inherent low sensitivity. Approximately 90 % of the measuring time is used by the spin system to return to its Boltzmann equilibrium after excitation, which is determined by (1)H-T1 in cross-polarized solid-state NMR experiments. It has been shown that sample doping by paramagnetic relaxation agents such as Cu(2+)-EDTA accelerates this process considerably resulting in enhanced sensitivity. Here, we extend this concept to Gd(3+)-complexes. Their effect on (1)H-T1 has been assessed on the membrane protein proteorhodopsin, a 7TM light-driven proton pump. A comparison between Gd(3+)-DOTA, Gd(3+)-TTAHA, covalently attached Cu(2+)-EDTA-tags and Cu(2+)-EDTA reveals a 3.2-, 2.6-, 2.4- and 2-fold improved signal-to-noise ratio per unit time due to longitudinal paramagnetic relaxation enhancement. Furthermore, Gd(3+)-DOTA shows a remarkably high relaxivity, which is 77-times higher than that of Cu(2+)-EDTA. Therefore, an order of magnitude lower dopant concentration can be used. In addition, no line-broadening effects or peak shifts have been observed on proteorhodopsin in the presence of Gd(3+)-DOTA. These favourable properties make it very useful for solid-state NMR experiments on membrane proteins.
authors.affiliation: Institute for Biophysical Chemistry, Centre for Biomolecular Magnetic Resonance, Goethe-University Frankfurt, Max von Laue Str. 9, 60438, Frankfurt am Main, Germany.
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Ullrich
authors.forename: Soraya
authors.initials: S
authors.lastname: Hölper
authors.forename: Clemens
authors.initials: C
authors.lastname: Glaubitz
mesh_terms: D003300:Copper / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004492:Edetic Acid / Q000737:chemistry; D005682:Gadolinium / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D017433:Protein Structure, Secondary; D012243:Rhodopsin / Q000737:chemistry; D025604:Rhodopsins, Microbial
chemical_list: D004220:Disulfides; D008051:Lipid Bilayers; D008565:Membrane Proteins; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D003300:Copper; D012243:Rhodopsin; D004492:Edetic Acid; D005682:Gadolinium