Accurate measurement of 3JHNHα couplings in small or disordered proteins from WATERGATE-optimized TROSY spectra

摘要

Provided that care is taken in adjusting the WATERGATE element of a ¹H-¹⁵N TROSY-HSQC experiment, such that neither the water magnetization nor the ¹H^α protons are inverted by its final 180° pulse, ³JHNHα couplings can be measured directly from splittings in the ¹H dimension of the spectrum. With band-selective ¹H decoupling, very high ¹⁵N resolution can be achieved. A complete set of ³JHNHα values, ranging from 3.4 to 10.1 Hz was measured for the 56-residue third domain of IgG-binding protein G (GB3). Using the H-N-C^α-H^α dihedral angles extracted from a RDC-refined structure of GB3, ³JHNHα values predicted by a previously parameterized Karplus equation agree to within a root-mean-square deviation (rmsd) of 0.37 Hz with the experimental data. Values measured for the Alzheimer's implicated Aβ^1-40 peptide fit to within an rmsd of 0.45 Hz to random coil ³JHNHα values.