Plays a major role in tight junction-specific obliteration of the intercellular space, through calcium-independent cell-adhesion activity. Can form homo- and heteropolymers with other CLDN. Homopolymers interact with CLDN3, but not CLDN1, homopolymers. Directly interacts with TJP1/ZO-1, TJP2/ZO-2 and TJP3/ZO-3 (By similarity). The disulfide bond is necessary for pore formation, but is not required for correct protein trafficking. Belongs to the claudin family.