Abstract
Background: The tight junction is an intercellular adhesion complex composed of claudins (CLDs), occludin, and the scaffolding proteins zonula occludens 1 (ZO-1) and its two paralogs ZO-2 and ZO-3. ZO-1 is a multifunctional protein that contains three PSD95/Discs large/ZO-1(PDZ) domains. A key functional domain of ZO-1 is the first PDZ domain (ZO-1(PDZ1)) that recognizes the conserved C-termini of CLDs. Methods: In this study, we confirmed that phosphoinositides bound directly to ZO-1(PDZ1) by biochemical and solution NMR experiments. We further determined the solution structure of mouse ZO-1(PDZ1) by NMR and mapped the phosphoinositide binding site onto its molecular surface. Results: The phosphoinositide binding site was spatially overlapped with the CLD-binding site of ZO-1(PDZ1). Accordingly, inositol-hexaphosphate (phytic acid), an analog of the phosphoinositide head group, competed with ZO-1(PDZ)-CLD interaction. Conclusions: The results suggested that the PDZ domain–phosphoinositide interaction plays a regulatory role in biogenesis and homeostasis of the tight junction.
Highlights
The tight junction (TJ), or zonula occludens, is the apical-most intercellular junction complex found in epithelial and endothelial cells
The binding ability of the selected PDZ domains, including zonula occludens 1 (ZO-1)(PDZ1), ZO-1(PDZ2), ZO-1(PDZ3), ZO-2(PDZ1), and afadin (PDZ) to phospholipids was examined by PIP StripTM nitrocellulose membrane overlay assay with glutathione S-transferase (GST)-tagged PDZ domains (Figure 2)
We found that several residues of ZO-1(PDZ1) involved in CLD binding may participate in PIP interaction
Summary
The tight junction (TJ), or zonula occludens, is the apical-most intercellular junction complex found in epithelial and endothelial cells. TJs are responsible for the formation of functional barriers. TJs regulate the passage of cells and solutes through the paracellular space [1,2]. TJs maintain the major barrier function of preserving the unique composition of chemical and biological substances at the apical and basolateral spaces of the cell layer. Molecules 2018, 23, x pathways, i.e., they regulate their own assembly and barrier function, and mechanobiological mechanobiological signals are transmitted. The tight junction is an intercellular adhesion complex composed of claudins (CLDs), occludin, and the scaffolding proteins zonula occludens 1 (ZO-1) and its two paralogs ZO-2 and ZO-3. Conclusions: The results suggested that the PDZ domain–phosphoinositide interaction plays a regulatory role in biogenesis and homeostasis of the tight junction
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