Abstract
Our recent study has shown that cellular junctions in myelin and in the epi-/perineruium that encase nerve fibers regulate the permeability of the peripheral nerves. This permeability may affect propagation of the action potential. Direct interactions between the PDZ&sub1; domain of zonula occludens (ZO&sub1; or ZO&sub2;) and the C-termini of claudins are known to be crucial for the formation of tight junctions. Using the purified PDZ&sub1; domain of ZO&sub2; and a variety of C-terminal mutants of peripheral nerve claudins (claudin-1, claudin-2, claudin-3, claudin-5 in epi-/perineurium; claudin-19 in myelin), we have utilized NMR spectroscopy to determine specific roles of the 3 C-terminal claudin residues (position -2, -1, 0) for their interactions with PDZ&sub1; of ZO&sub2;. In contrast to the canonical model that emphasizes the importance of residues at the -2 and 0 positions, our results demonstrate that, for peripheral nerve claudins, the residue at position -1 plays a critical role in association with PDZ&sub1;, while the side-chain of residue 0 plays a significant but lesser role. Surprisingly, claudin-19, the most abundant claudin in myelin, exhibited no binding to ZO&sub2;. These findings reveal that the binding mechanism of claudin/ZO in epi-/perineurium is distinct from the canonical interactions between non-ZO PDZ-containing proteins with their ligands. This observation provides the molecular basis for a strategy to develop drugs that target tight junctions in the epi-/perineurium of peripheral nerves.