Parameter name	Description	Floating/fixed
${\omega }_D$	Chemical shifts of down state	Fixed for five selected residues (13C only) and used in Eq. S3
$\mathrm{\Delta }{\omega }_{UD}={\omega }_D-{\omega }_U$	Difference in chemical shifts between up and down states	Fixed for five selected residues (13C and 1H) and floating for others
$\mathrm{\Delta }{\omega }_{CD}={\omega }_D-{\omega }_C$	Difference in chemical shifts between states C and D	Floating
$R_{MQ,D},R_{MQ,U},R_{MQ,C}$	Multiple quantum (MQ) relaxation rates for states D, U, C	Floating, but assumed the same for a given methyl
$k_{ex,DU},k_{ex,UC},p_U,p_C$	Exchange rates and populations	Floating global parameters