Enzymes involved in neuropeptide biosynthesis and regulation

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A wide variety of proteins in neuronal, endocrine and immune tissues undergo proteolytic processing. Many of these proteins and peptides are intercellular messengers. Most neuroendocrine peptides are synthesized from precursor proteins. Post-translational processing of these precursors is a key step in the production of biologically active peptides. In the majority of cases this occurs by proteolysis of the precursors at 'classical' cleavage sites involving endopeptidases of the subtilisin family. A subset of bioactive peptides are generated by processing at 'non-classical' cleavage sites; the protease(s) responsible for these cleavages have not been well explored. Members of the metalloendoprotease family are thought to be involved in non- classical processing. Among them, endothelin converting enzyme-2 (ECE-2) is a good candidate since it exhibits functional properties that are consistent with it being a neuropeptide biosynthetic enzyme. In this grant application we propose to examine the hypothesis that "ECE-2 is neuropeptide processing enzyme that generates novel bioactive peptides by non-classical processing". The specific aims are, (i) to characterize the biochemical and enzymological properties of ECE-2, (ii) to study the behavioral phenotype of animals lacking ECE-2 including addictive behaviors, and (iii) to examine the peptide profile in mice lacking ECE-2 using differential isotopic labeling and mass spectrometry. These studies are synergistic and will expand our current knowledge of neuropeptide processing by providing information about novel neuropeptides. Furthermore, findings from these studies will form a basis for future research exploring the functions of these novel neuropeptides in vivo. Since a variety of neuropeptides are involved in normal functioning of the brain, understanding the mechanisms that regulate their endogenous levels becomes a prerequisite to the development of strategies for the treatment of a variety of pathologies including neurodegenerative disorders and drug addiction.