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 CLDN1 and CLDN2 homopolymers. Directly interacts with TJP1/ZO-1, TJP2/ZO-2 and TJP3/ZO-3 (By similarity). Belongs to the claudin family.