TABLE 1.

Amino acid residues of the first extracellular domain of claudin-2 that were selected for cysteine mutagenesis

Residue	Rationale for selection (based on observations on homologous residues in other claudin isoforms)	Reference
Tyr35	R32D in claudin-10a decreases anion selectivity	Ref. 7
	D104S in claudin-16 partially inhibits cation permeation	Ref. 27
His57	D55K in claudin-15 converts from cation to anion selectivity	Ref. 6
	Q57E in claudin-19 causes familial hypomagnesemia with hypercalciuria and nephrocalcinosis	Ref. 22
Asp65	K65D of cation-blocking claudin-4 eliminates discrimination against Na+	Ref. 6
	D65N in claudin-2 abolishes a cation-binding site within the pore lumen	Ref. 5
Ile66	Asp65 and Glu63, respectively, in claudin-10b and claudin-16, which are both highly cation-selective, are both negatively charged
	E64K in claudin-15 converts from cation to anion selectivity	Ref. 6