Fig. 4

Binding affinity titration curves for yeast-displayed wild type and His variant CA proteins. Y-axis denotes ratio of Mean Fluorescence Unit (MFU) values measured via flow cytometry at a given EGFR concentration to MFUs measured at saturating EGFR concentration (50–100 nM) for respective wild type and His variant CAs. X-axis denotes EGFR concentration. Measured:saturating MFU ratios for EGFR binding at pH 7.4 denoted by blue markers; MFU ratios for EGFR binding at pH 5.5 denoted in red. Data points represent average values for two independent trials. Respective blue and red lines connect data points for wild type CA binding to EGFR at pH 7.4 and pH 5.5. Error bars, which appear for T49H mutant data, denote standard deviation for two independent trials