Hydrolysis of peptide hormones by endothelin-converting enzyme-1. A comparison with neprilysin

Disulfide bonds in big ET-1 are essential for the specific cleavage at the Trp(21)-Val(22) bond by soluble endothelin converting enzyme-1 from baculovirus/insect cells

Endothelin converting enzyme-1 (ECE-1) is a type II integral membrane protein and a zinc metalloendopeptidase. ECE-1 generates endothelin-1 (ET-1), the most potent vasoconstrictor yet discovered, by specific proteolytic processing of a precursor peptide, big ET-1. An insect cell expression system, which generates up to 4.3 mg of a secreted, soluble form of ECE-1 (solECE-1) per liter culture medium, has been established and solECE-1 was purified to homogeneity using five chromatographic steps. SolECE-1 expressed in insect cells could be suitable for X-ray structure determination as it is much less glycosylated than solECE-1 from mammalian cells. SolECE-1 from both sources, nonetheless, has comparable enzymatic properties. Despite apparent structural similarities, ECE-1 cleaves big ET-1 exclusively between Trp(21) and Val(22), in contrast to neprilysin, which cleaves big ET-1 at various sites. However, when linear big ET-1, in which the formation of disulfide bonds has been prevented by alkylation of the four cysteines, was used as substrate, it was cleaved by solECE-1 at multiple sites. This result indicates that secondary/tertiary structure of big ET-1 induced by disulfide bonds is essential for the specific cleavage of the Trp(21)-Val(22) bond by ECE-1. A continuous, fluorescent ECE-1 assay has been developed using a novel substrate, 2-aminobenzoyl-Arg-Pro-Pro-Gly-Phe-Ser-Pro-(p-nitro-Phe(8))-Arg. This simple and rapid assay can greatly facilitate discovery of novel ECE inhibitors useful as pharmaceutical agents.

Molecular identification and characterization of novel membrane-bound metalloprotease, the soluble secreted form of which hydrolyzes a variety of vasoactive peptides

One class of zinc metalloproteases, represented by neutral endopeptidase 24.11 and endothelin-converting enzyme, has been shown to be involved in proteolytic activation or inactivation of many regulatory peptides. Here, we report molecular cloning and characterization of a novel member of this type II membrane-bound metalloprotease family, termed soluble secreted endopeptidase (SEP). Alternative splicing results in the generation of another transcript, SEP(Delta), which lacks a 69-base pair nucleotide segment following the transmembrane helix. Both SEP and SEP(Delta) mRNA are detected in all mouse tissues examined. Transfection of an SEP cDNA expression construct resulted in the expression of the membrane-bound form of SEP in the early secretory pathway as well as the soluble secreted form of the enzyme in the culture medium. In contrast, transfection of the SEP(Delta) cDNA only results in the expression of the membrane-bound form. In vitro enzymological analysis of the recombinant soluble form of SEP demonstrated that it hydrolyzes a variety of vasoactive peptides, including endothelin-1, atrial natriuretic peptide, and angiotensin I. This activity of SEP was inhibited by phosphoramidon and the neutral endopeptidase 24.11 specific inhibitor thiorphan, but it was only partially inhibited by the endothelin-converting enzyme specific inhibitor FR901533. These findings suggest that SEP is a novel metalloprotease that possesses a broad substrate specificity and that it may be involved in the metabolism of biologically active peptides intracellulary as well as extracellularly.

Sequencing, expression and biochemical characterization of the Porphyromonas gingivalis pepO gene encoding a protein homologous to human endothelin-converting enzyme

We have determined the nucleotide sequence of the clone pAL2 obtained from Porphyromonas gingivalis 381 in the previous study [Ansai et al. (1995) Microbiology 141, 2047-20521. The DNA sequence analysis of this fragment revealed one complete ORF and one incomplete ORF. The ORF encoded a protein (PgPepO) of 690 amino acids with a calculated molecular weight of 78796. The deduced amino acid sequence exhibited a significant homology with human endothelin-converting enzyme (ECE)-1. Recombinant PgPepO was purified to homogeneity and characterized. The purified enzyme was strongly inhibited by phosphoramidon, and converted big endothelin-1 to endothelin-1. Furthermore, the purified PgPepO strongly cross-reacted with a monoclonal antibody against rat ECE-1. These results indicate that PgPepO has striking similarity to mammalian ECE in structure and function.

Endothelin antagonists for hypertension and renal disease

The endothelin system has been implicated in the pathogenesis of arterial hypertension and renal disorders. Endothelin-1, the predominant isoform of the endothelin peptide family, regulates vasoconstriction and cell proliferation in tissues both within and outside the cardiovascular system through activation of Gi-protein-coupled ET(A) and ET(B) receptors. Endothelin synthesis is regulated through autocrine mechanisms by endothelin converting enzymes, chymases, and non-endothelin converting enzyme metalloproteases. In-vitro experiments have demonstrated that endothelin-1 stimulates growth in vascular smooth muscle and in the kidney. Recent studies indicate that endothelin mRNA and protein are also increased in vivo in the kidney and vasculature in hypertension and renal disease. Studies using molecular or pharmacological inhibition of the endothelin system demonstrate that endothelin-1 contributes to the functional and structural changes associated with arterial hypertension and glomerulosclerosis, and that these effects are only in part dependent on blood pressure. These experimental studies and first clinical trials suggest that endothelin antagonists may offer therapeutic potential to reduce end-organ damage in diseases associated with vascular remodeling and renal injury.