Cofactor-Dependent Amine Oxidations

Sayre, Lawrence

Abstract

The copper-containing amine oxidases (CAOs) comprise a ubiquitous class of enzymes in all living organisms. In plants and mammals, CAOs play important roles in metabolizing biogenic amines involved in growth, cell division, differentiation, and the stress response, where metabolism in some cases has cytotoxic consequences. All CAOs utilize a quinone cofactor derived postranslationally from an active-site tyrosine residue to mediate a transaminative conversion of primary amines to aldehydes. Studies using cofactor models in the past grant periods have inspired the discovery of new types of enzyme-activated mechanisms of inhibition. These studies, along with development of other traditional inactivation strategies, have resulted in highly promising degrees of inhibitor selectivity. The selectivity being achieved is discriminating not only between the flavin- and quinone-dependent enzymes, but also among a range of CAOs that have different substrate-structure preferences. Since the time of the last renewal, the genetic basis of the two general classes of human CAOs has been revealed: (i) the trihydroxyphenylalanine quinone (TPQ)-dependent class AOC 1 (the human kidney diamine oxidase), AOC 2, and AOC 3, the latter coincidental with the human vascular adhesion protein-1 (HVAP-1), and (ii) four lysyl oxidase-like (LOXL) proteins in addition to classical LOX. In the next grant period, there will be increased focus on refining inhibitor selectivity for the human enzymes, particularly the kidney/placental diamine oxidase, the soluble and tissue-bound semicarbazide- sensitive monoamine oxidases, and lysyl oxidase. The new aims include the development of sensitive fluorometric assays for detecting and localizing mammalian CAOs, an exploration of new inhibitor selectivity and prodrug constructs, the use of x-ray crystallographic information (through collaboration) for refinement of substrate and inhibitor binding models constructed by molecular modeling, and the use of spectroscopy and mass spectrometry to identify the structural basis of irreversible inhibitor action. Studies on the nature of biogenesis of the (TPQ) cofactor will additionally be completed. ? ?

Public Health Relevance

OF THIS RESEARCH TO PUBLIC HEALTH ? ? The copper amine oxidases have become important pharmaceutical targets on account of the emerging recognition of their key physiological roles in aspects of inflammation, immune modulation, fibrosis in arthritis and atherosclerosis, and in late-stage complications of diabetes and cardiovascular disease. It is thus important to understand the functioning of these enzymes, both from a mechanistic view and in terms of the structural basis of substrate recognition and the action of inhibitors that can serve a leads in eventual drug development. ? ? ?