Читать книгу Introduction to the Human Cell - Danton PhD O'Day - Страница 24

The four major proteins found in tight junctions are called claudins, occludins, junctional adhesion molecule-1 (JAM-1) and zonula occludin proteins 1-3 (ZO1-3). These are shown in the following figure (Figure 3.7). The claudins are small 26 kDa (kiloDalton) proteins that are critical to the structural integrity of tight junctions. Occludins are larger at 65 kDa and are the major proteins found in these junctional complexes. These integral proteins are not essential since knockout mutants for occludin proteins do not prevent tight junction formation. It has been suggested that they are accessory proteins that don’t provide any structural basis. Knocking out ZO1 interferes with tight junction formation indicating it is a critical protein.

Figure 3.7. A diagrammatic representation of the organization of tight junction proteins.

The zonula occludin protein ZO1 was the first cloned tight junction protein. It lies at the inner side of the cell membrane where it organizes the other junctional adhesion molecules. It is indicated as one of the linker proteins in the figure. ZO1 and occludin both share an interesting and important function: they signal the integrity of the junctional adhesion complex. Thus they make the cell aware of its status regarding its adhesion with other cells.