The N-terminal segment of endothelin-converting enzyme (ECE)-1b contains a di-leucine motif that can redirect neprilysin to an intracellular compartment in Madin-Darby canine kidney (MDCK) cells

Endothelin-converting enzyme (ECE)-1 is a membrane-bound metallopeptidase of the neprilysin (NEP) family. ECE-1 is responsible for the conversion of inactive big-endothelins into active endothelins. Three different isoforms of human ECE-I (ECE-la, ECE-lb and ECE-lc) have been identified, They differ in their N-terminal cytosolic regions, have distinct tissue distribution and intracellular localization. ECE-la and ECE-le are both located at the cell surface whereas ECE-lb is targeted to an intracellular compartment. To better understand the nature of the signal responsible for the targeting of ECE-lb to the intracellular compartment, we have constructed several ECE/NEP chimaeric proteins and expressed them by transfection into Madin-Darby canine kidney (MDCK) cells, This allowed us to identify a nine amino acid segment in the cytosolic tail of ECE-1b that is sufficient to relocate NEP from the cell surface to an intracellular compartment. Site-directed mutagenesis on these chimaeras led to the identification of two leucine residues as part of the intracellular retention signal.