Fig. 4.

Dipeptides target the C terminus of the peptide to catalyze peptide exchange. (A) Exchange of K^b-bound high-affinity peptide SIINFEKL and its C-terminally modified variants SIINFEKG and SIINFEKA were measured in the presence of 10 mM GL or GM or without any dipeptide by measuring the association rate (k_on) of SIINFEK_TAMRAL in a fluorescence anisotropy assay. (B) Analogous experiment comparing the exchange of K^b–SIINFEKL-Cdel, K^b–SIINFEKL-Ndel, and K^b–SIINFEKL for SIINFEK_TAMRAL. All numerical values are shown in Table S2. (C) Mechanistic model of dipeptide-facilitated peptide exchange (see text).