claudin1

Claudin-1 is a member of the claudin family of integral membrane proteins that form the backbone of tight junctions in epithelial and endothelial cells. It is encoded by the CLDN1 gene in humans and contributes to the paracellular barrier that regulates the movement of ions and small solutes between adjacent cells. As a core component of tight junction strands, Claudin-1 helps define tissue-specific barrier properties.

Structurally, Claudin-1 is a four-pass transmembrane protein with two extracellular loops that participate in strand formation and selective charge interactions. The cytoplasmic N- and C- termini help anchor the protein to the tight junction complex and interact with cytosolic scaffold proteins such as ZO-1, ZO-2, and ZO-3. The C-terminus contains a PDZ-binding motif that facilitates these interactions, and the assembly and function of Claudin-1-containing junctions are modulated by phosphorylation and trafficking pathways.

Expression of Claudin-1 is high in the epidermis and is important for maintaining the skin’s barrier function. It is also present in various other epithelia, including components of the respiratory and digestive tracts, where it contributes to selective permeability. Proper localization and regulation of Claudin-1 are essential for preventing unwanted paracellular leak; disruption can weaken barriers and contribute to disease processes.

Clinical relevance of CLDN1 includes associations between abnormal expression or function and skin disorders and inflammatory conditions, as well as altered patterns in certain cancers. While rare CLDN1 mutations have been described, changes in Claudin-1 levels or distribution across tissues are a focus of ongoing research into barrier biology and pathogenesis.

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