Which protein is primarily associated with tight junctions?

Tight junctions are essential structures in epithelial and endothelial cells that regulate the passage of substances between cells and maintain the integrity of the tissue barrier. The primary proteins associated with tight junctions are claudins and occludin. Occludin, in particular, plays a crucial role in the formation and maintenance of these junctions. It is involved in sealing the space between cells, thus preventing the leakage of materials in the intercellular space.

Occludin interacts with other proteins in the tight junction complex and helps in signaling pathways that can influence cell function and tissue homeostasis. Its structure, with multiple transmembrane domains, allows it to effectively span the cell membrane and contribute to the tight junction's barrier properties. This unique role underscores why occludin is a key marker of tight junctions and illustrates its importance in cellular integrity and signaling mechanisms.

In contrast, while collagen provides structural support in various tissues, actin is mainly involved in the cytoskeleton and cellular movement, and keratin is associated with the formation of epithelial structures, none of these proteins have the specific role that occludin possesses in tight junction formation and function.