Fig. 6

Binding histogram overlays showing that CA His mutants do not undergo irreversible conformational changes at low pH. X-axis denotes phycoerythrin fluorescence corresponding to EGFR binding. Y-axis denotes number of yeast cells in sample analyzed with given level of EGFR binding. Wild type (red-pH 7.4, pink-pH 5.5) incubated with 1.5 nM EGFR in all figure panels. F48H (dark green-pH 7.4, bright green-pH 5.5) incubated with 4 nM EGFR, T49H incubated with 1.5 nM EGFR (blue-pH 7.4, cyan-pH 5.5), and F48H/T49H (purple-pH 7.4, lavendar-pH 5.5) incubated with 12 nM EGFR. All incubations with EGFR performed in pH 7.4 buffer. The preceding pH values in parentheses and those appearing in the figure denote ligand-free incubation buffer pH values. Unlabeled, negative control yeast population histograms appear in orange in all figure panels. As shown in Additional file 1: Figure S3, F48H and F48H/T49H were displayed at lower levels than T49H and wild type CA