A claudin is a member of a family of four-pass membrane proteins that assemble into tight junction strands between neighbouring cells. The choice of claudins helps determine which ions and small solutes can pass through the pathway between epithelial cells. A tight junction can therefore be selectively permeable rather than an absolutely impermeable weld.[ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 19, Tight Junctions Form a Selective Permeability Barrier Across Epithelial Cell Sheets
The structural role was demonstrated by adding claudin-1 or claudin-2 to mouse fibroblasts that lacked tight junctions. Freeze-fracture electron microscopy revealed extended strand networks in the modified cell membranes. Coexpression recruited occludin to the strands. Building recognizable junction strands in this simplified setting supplied stronger evidence for a construction role than finding a protein near an existing junction alone.[ref]
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