Native exchange NMR None residues that exhibit significant protection (no exchange for > 2 hours) MQEAVLQLIEVQLAQEEVTESPLGGDENAQLHASGYYALFVDTVPDDVKRLYTEAATSDFAALAQTAHRLKGVFAMLNLVPGKQLCETLEHLIREKDVPGIEKYISDIDSYVKSLL

The proton-exchange experiments were carried out on a Bruker DMX 600 spectrometer at 293 K. The 15N-labeled YojN-HPt sample was lyophilized and dissolved in the same volume of ice-cold D2O. A series of [1H,15N]-HSQC spectra were acquired every 30 minutes during the first two hours and thereafter every two hours for the following two days.