Regulation of Heterotypic Claudin Compatibility

Abstract

Tissue barrier function is directly mediated by tight junction transmembrane proteins known as claudins. Cells that form tight junctions typically express multiple claudin isoforms which suggests that heterotypic (head-to-head) binding between different claudin isoforms may play a role in regulating paracellular permeability. However, little is known about motifs that control heterotypic claudin compatibility. We found that although claudin-3 and claudin-4 were heteromerically compatible when expressed in the same cell, they did not heterotypically interact despite having extracellular loop (EL) domains that are highly conserved at the amino acid level. Claudin-1 and -5, which were heterotypically compatible with claudin-3, did not heterotypically bind to claudin-4. In contrast, claudin-4 chimeras containing either the first EL domain or the second EL domain of claudin-3 were able to heterotypically bind to claudin-1, claudin-3, and claudin-5. Moreover, a single point mutation in the first extracellular loop domain of claudin-3 to convert Asn 44 to the corresponding amino acid in claudin-4 (Thr) produced a claudin capable of heterotypic binding to claudin-4 while still retaining the ability to bind to claudin-1 and -5. Thus, control of heterotypic claudin-claudin interactions is sensitive to small changes in the EL domains.

Lecture

“…37 Co-culture of HeLa cells expressing different claudin genes revealed that while CLDN1 and CLDN5 were heterotypically interacting with CLDN3, they would not heterotypically bind to CLDN4, demonstrating considerable selectivity in heterotypic claudin-claudin interactions. 38 39 FRAP studies suggest that claudin molecules assembled in tight junctions have limited mobility, 40 consistent with their known heteromeric interactions with scaffold proteins in the tight junction.…”

Mosaic expression of claudins in thick ascending limbs of Henle results in spatial separation of paracellular Na + and Mg 2+ transport

“…Whether this property is important for the cldn16 selectivity filter is unknown as yet. However, the ECS2 of claudins has been described as an important determinant of trans-interaction capability (39,40). The use of claudin chimeras to identify the function of particular claudin segments involves a certain risk of misfolding.…”

A Key Claudin Extracellular Loop Domain is Critical for Epithelial Barrier Integrity

“…48 Also, heterotypic claudin-claudin specificity is dictated by motifs in both the first and second EL domains. 36 Thus, a likely model is that both claudin EL domains act in concert to mediate heterotypic binding of claudins between adjacent cells.…”