Neural precursor cell expressed developmentally downregulated gene 4-like (NEDD4L) or NEDD4-2 is an enzyme (ubiquitin ligase) of the NEDD4 family. In human the protein is encoded by the NEDD4L gene. In mouse the protein is commonly known as NEDD4-2 and the gene Nedd4-2. NEDD4-2 has been shown to ubiquitinate and therefore down regulate the epithelial sodium channel (ENaC) in the collecting ducts of the kidneys, therefore opposing the actions of aldosterone and increasing salt excretion. In Liddle's Syndrome NEDD4 is unable to bind to the ENaC and lead to salt retention and hypertension occur. NEDD4L belongs to the NEDD4 family of E3 HECT domain ubiquitin ligases. It is the closest homologue of NEDD4, the prototypic member of the family and probably arose as a result of gene duplication. While NEDD4 orthologues are present in all eukaryotes, NEDD4L proteins are limited to vertebrates. NEDD4L proteins are known to be involved in regulating many membrane proteins via ubiquitination and endocytosis. NEDD4L protein is expressed widely. The primary targets of NEDD4-2 include the epithelial sodium channel (ENaC), the Na+-Cl- co-transporter (NCC), and the voltage gated sodium channels (Navs), although additional targets are predicted from in vitro studies. NEDD4-2 gene in mice is essential for animal survival and the polymorphisms in NEDD4L are associated with human hypertension. Protein architecture The NEDD4-2 protein consists of an amino-terminal Ca2+-phospholipid binding domain (C2), 4 WW domains (protein-protein interaction domains) and the carboxyl-terminal HECT domain (ubiquitin ligase domain). The WW domains in the protein are responsible for binding the substrates, regulatory proteins and adaptors. These domains generally recognize PPxY (or similar) motifs in the target proteins. Expression Human NEDD4L gene is located on chromosome 18q12.31 with 38 exons that transcribe multiple splice variants of NEDD4L. The protein expressed in the brain, lung, heart and the kidney contains a C2 domain. Three predominant forms of NEDD4L are isoform I containing a novel C2 domain with a start codon in exon1, isoform II with an intact conserved C2 domain consisting of an alternate start codon in exon 1 upstream of the actual start codon of the isoform 1, and isoform III lacking a C2 domain due to exon 2a–3 splicing. Isoform 1 is found to be abundant in kidney and adrenal gland whereas isoform 2 is predominantly found in the lungs. The antibodies specific to NEDD4-2 recognize two species of ~110-115 kDa in most tissues, with one being variable depending