Comparison of mucosal absorption-enhancing activity between a claudin-3/-4 binder and a broadly specific claudin binder

► A polypeptide, C-CPE, is a claudin-3/-4 binder. ► A C-CPE mutant, m19, is a claudin-1/-2/-4/-5 binder. ► C-CPE and m19 showed different mucosal absorption-enhancing activity. ► We may modify mucosal absorption-enhancing activity by modulating claudin specificity.