Claudin

Claudins are a family of proteins that are the most important components of the tight junctions, where they establish the paracellular barrier that controls the flow of molecules in the intercellular space between the cells of an epithelium. They have four transmembrane domains, with the N-terminus and the C-terminus in the cytoplasm.

Structure

Claudins are small (20–27 kilodalton (kDa)) transmembrane proteins which are found in many organisms, ranging from nematodes to human beings, and are very similar in their structure, although this conservation is not observed on the genetic level. Claudins span the cellular membrane 4 times, with the N-terminal end and the C-terminal end both located in the cytoplasm, and two extracellular loops which show the highest degree of conservation. The first extracellular loop consists on average of 53 amino acids and the second one, being slightly smaller, of 24 amino acids. The N-terminal end is usually very short (4–10 amino acids), the C-terminal end varies in length from 21 to 63 and is necessary for the localisation of these proteins in the tight junctions. It is suspected that the cysteines of individual or separate claudins form disulfide bonds. All human claudins (with the exception of Claudin 12) have domains that let them bind to PDZ domains of scaffold proteins.

CLDN1

Claudin-1 is a protein that in humans is encoded by the CLDN1 gene. It belongs to the group of claudins.

Function

Tight junctions represent one mode of cell-to-cell adhesion in epithelial or endothelial cell sheets, forming continuous seals around cells and serving as a physical barrier to prevent solutes and water from passing freely through the paracellular space. These junctions are composed of sets of continuous networking strands in the outwardly facing cytoplasmic leaflet, with complementary grooves in the inwardly facing extracytoplasmic leaflet. The protein encoded by this gene, a member of the claudin family, is an integral membrane protein and a component of tight junction strands. Loss of function mutations result in neonatal ichthyosis-sclerosing cholangitis syndrome.

Interactions

CLDN1 has been shown to interact with CLDN5 and CLDN3.

References

Further reading