FIGURE 2.

Ecl2 with the downstream transmembrane domain is sufficient enough to express optimal binding activity to Cpe30. Biotin-Cpe30 was immobilized on an SA chip as the ligand, and Cldn-4 deletion mutant proteins fused to GST were tested as analytes. A, schematic diagram of full-length claudin-4 and its mutants, with the structural domains labeled above. B, SDS-PAGE analysis of purified GST-Cldn-4 mutant fusions. C, overlay of the sensorgrams from different analytes at medium concentration. GST-only protein did not bind Cpe30 (not shown). Specific binding was identified by subtraction of the control channel from the assay channel; this processing was applied to the rest of experiments in this study.