Claudin-1 also known as CLDN1 is a member of the claudin family, which forms the backbone of tight junctions in epithelial and endothelial cells, regulating paracellular transport. Structurally, claudin-1 spans the membrane with four transmembrane domains and two extracellular loops, which are critical in forming tight junction strands that create selective barriers between cells. This unique structure allows claudin-1 to participate in maintaining cellular polarity and controlling ion permeability, vital functions in organs like the liver and kidney, where claudin-1 is most abundantly expressed. The structural configuration of claudin-1 also facilitates interactions with other tight junction proteins, such as occludins and junctional adhesion molecules, enabling complex tissue compartmentalization. Mutations in claudin-1 are linked to neonatal ichthyosis-sclerosing cholangitis syndrome, highlighting its role in tissue integrity.