Secretion of endothelin converting enzyme-1a: the hydrophobic signal anchor domain alone is not sufficient to promote membrane localization.

Endothelin converting enzyme-1 (ECE-1) is a type II membrane protein that is important for the proteolytic activation of big endothelin-1 to endothelin-1. Although the highly conserved zinc-binding motif is known to be located in the extracellular domain, the role(s) of the N-terminal and membrane-spanning signal anchor domains in the biosynthesis and function of ECE-1 isoforms, ECE-1a, ECE-1b, and ECE-1c, remain undetermined. In this study, we provide evidence that the deletion of the cytoplasmic N-terminal tail (residues 1-55) of ECE-1a results in the cleavage of a potential signal peptide located in the signal anchor domain leading to the partial secretion of the recombinant enzyme into the media. However, the truncation of N-terminal and/or signal anchor domain does not affect the activity of ECE-1a. Therefore, our results demonstrate that the hydrophobic signal anchor domain alone is not sufficient for the membrane anchoring of ECE-1a and that the N-terminal domain of ECE-1a is important for membrane targeting as well as the intracellular localization of the enzyme.