Solution structure of a Nedd4 WW domain-ENaC peptide complex

Nedd4 is a ubiquitin protein ligase composed of a C2 domain, three (or four ) WW domains and a ubiquitin ligase Hect domain. Nedd4 was demonstrated to bind the epithelial sodium channel (alpha beta gamma ENaC), by association of its WW domains with PY motifs (XPPXY) present in each ENaC subunit, and to regulate the cell surface stability of the channel. The PY motif of beta ENaC is deleted or mutated in Liddle syndrome. a hereditary form of hypert ension caused by elevated ENaC activity. Here we report the solution struct ure of the third WW domain of Nedd4 complexed to the PY moth-containing reg ion of beta ENaC (TLPIPGTPPPNYDSL, referred to as beta P2). A polyproline t ype II helical conformation is adopted by the PPPN sequence. Unexpectedly, the C-terminal sequence YDSL forms a helical turn and both the tyrosine and the C-terminal leucine contact the WW domain. This is unlike other proline -rich peptides complexed to WW domains, which bind in an extended conformat ion and lack molecular interactions with residues C-terminal to the tyrosin e or the structurally equivalent residue in non-PY motif WW domain targets. The Nedd4 WW domain-ENaC beta P2 peptide structure expands our understandi ng of the mechanisms involved in WW domain-ligand recognition and the molec ular basis of Liddle syndrome.