Biochemistry and Physiology of Peptide Amidation

University Of Connecticut Sch Of Med/Dnt, Farmington CT

Investigators

Linked publications & trials

Abstract

? DESCRIPTION (provided by applicant): With purification of the first neuropeptide, vasopressin, it was clear that peptides play an essential role in our ability to respond to environmental changes. Production of bioactive peptides involves a carefully orchestrated set of enzymatic reactions, leading to their storage in secretory granules. Peptidylglycine ?-amidating monooxygenase (Pam), an integral membrane protein, is the only enzyme known to amidate peptides, a modification usually essential for receptor binding. PamKO mice are not viable and Pam+/- mice exhibit anxiety and thermoregulatory deficits, with older animals exhibiting impaired ability to handle a glucose load. While our analysis of Pam+/- mice revealed only a small decrease in amidated peptide levels, their copper homeostasis was altered. Using a neuroendocrine cell line engineered to allow control of PAM expression, we found that PAM alters cytoskeletal organization and regulated secretory pathway function. These observations led us to consider additional functions for PAM. A clue to these functions came when we found active integral membrane PAM in Chlamydomonas reinhardtii, a unicellular eukaryotic alga. Rat and Chlamydomonas PAM exhibit strikingly similar enzymatic properties and subcellular localizations, including their presence in cilia. Molecular oxygen, luminal copper and acidic pH are essential to PAM function. The P-type ATPase that pumps copper into the secretory pathway and the vacuolar ATPase (V-ATPase) that acidifies the luminal environment are evolutionarily ancient. We hypothesize that PAM interacts with both of these pumps. Using purified recombinant proteins, corticotrope tumor cells and Pam+/- mice, we will test the hypothesis that pH-dependent interactions between PAM and Atp7a enable direct transfer of copper from Atp7a to PAM. We will use Chlamydomonas to identify ancient interactions of PAM with the transporters needed to support its catalytic activity and to determine the role of PAM in cilia. Using pituitaries from Pam+/- mice and mouse embryo fibroblasts from PamKO mice, we will determine how interactions between PAM and the V-ATPase affect the regulated secretory pathway. Our hypothesis that PAM plays a role in coupling nutrient sensing to hormonal signaling networks, helping to adjust growth and development programs to an environment that is constantly changing, is novel. Knowledge of the role played by PAM in this coupling will identify sites for targeted pharmacological intervention. The recent association of mutations in hPAM with Type 2 diabetes and the endocrine deficits associated with ciliopathies and altered copper homeostasis indicate that there is much to be learned.