Measurement of HN-H alpha J couplings in calcium-free calmodulin using new 2D and 3D water-flip-back methods.
Two new methods are described for the measurement of three-bond JHNH alpha couplings in proteins isotopically enriched with 15N. Both methods leave the water magnetization in an unsaturated state, parallel to the z-axis, and therefore offer significant enhancements in sensitivity for rapidly exchanging backbone amide protons. The J couplings can be measured either from a set of constant-time 2D 1H-15N HMQC spectra, which are modulated in intensity by JHNH alpha, or from a water-flip-back version of the 3D HNHA experiment. The method is demonstrated for a sample of calcium-free calmodulin. Residues Lys75-Asp80 have JHNH alpha values in the 6-7 Hz range, suggesting that a break in the 'central helix' occurs at the same position as previously observed in solution NMR studies of Ca(2+)-ligated calmodulin.
Kuboniwa
H
H
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520.
Grzesiek
S
S
Delaglio
F
F
Bax
A
A
D002147:Calmodulin / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D014867:Water / Q000737:chemistry
D002147:Calmodulin; D014867:Water