A simple method to quantitatively measure polypeptide J-HNHα coupling constants from TOCSY or NOESY spectra

A simple linear relationship between the J(H)N(H) alpha coupling constant and the linewidth (Delta nu(1/2)) of in-phase NMR peaks has been identified. This relationship permits the rapid and accurate determination of polypeptide J(H)N(H) alpha coupling constants from a simple inspection of amide cross peaks in homonuclear H-1 TOCSY or H-1 NOESY spectra. By using the appropriate set of processing parameters we show that J(H)N(H) alpha = 0.5(Delta nu(1/2))-MW/5000 + 1.8 for TOCSY spectra and J(H)N(H) alpha=0.6(Delta nu(1/2))-MW/5000-0.9 for NOESY spectra, where Delta nu(1/2) is the half-height linewidth in Hz and MW is the molecular weight of the protein in Da. The simplicity of this relationship, combined with the ease with which Delta nu(1/2) measurements can be made, means that J(H)N(H) alpha coupling constants can now be rapidly determined (up to 100 measurements in less than 30 min) without the need for any complex curve-fitting algorithms. Tests on 11 different polypeptides involving more than 650 separate J(H)N(H) alpha measurements have shown that this method yields coupling constants with an rmsd error (relative to X-ray data) of less than 0.9 Hz. Furthermore, the correlation coefficient between the predicted NMR coupling constants and those derived from high-resolution X-ray crystal structures is typically better than 0.89. These simple linear relationships have been found to be valid for peptides as small as 1 kDa to proteins as large as 20 kDa. Despite the method's simplicity, these results are comparable to the accuracy and precision of the best techniques published to date.