Estimation of $$^{3}J_{HN\hbox{-}H\alpha}$$ and $$^{3}J_{H\alpha\hbox{-}H\beta}$$ coupling constants from heteronuclear TOCSY spectra

Abstract

3 J proton–proton coupling constants bear information on the intervening dihedral angles. Methods have been developed to derive this information from NMR spectra of proteins. Using series expansion of the time dependent density matrix, and exploiting the simple topology of amino acid spin-systems, formulae for estimation of $$^{3}\hbox{J}_{{\rm HN-H}\alpha}$$ and $$^{3}\hbox{J}_{{\rm H}\alpha {\rm -H}\beta}$$ from HSQC-TOCSY spectra are derived. The results obtained on a protein entailing both α-helix and β-sheet secondary structure elements agree very well with J-coupling constants computed from the X-ray structure. The method compares well with existing methods and requires only 2D spectra which would be typically otherwise recorded for structural studies.