Molecular basis for cation selectivity in claudin-2-based pores.

Claudins are transmembrane tight junction proteins that form paracellular pores. Claudins regulate the permeability of small inorganic ions and are selective on the basis of charge. We have developed an inducible expression system to measure the permeability of claudin-2 and have found that claudin-2 forms highly cation-selective paracellular pores. The basis of this charge selectivity is likely to be the presence of a negatively charged binding site within the lumen of the pore. This may be a general mechanism by which claudins achieve selectivity.