Side chain 3 J Hα,Hβ scalar couplings were calculated using the residue-specific Karplus equation parameters given in Table of Pérez et al. We used the residue-specific parameters as opposed to the "consensus" parameters because the scalar couplings for serine and threonine are systematically and significantly lower than all other residues due to the electron-withdrawing nature of the oxygen substituent attached to the Cβ atom in these residues.