Rational Approaches to the Design of Mechanism-Based Inhibitors of S-Adenosylhomocysteine Hydrolase

Abstract

Crucial to the rational design of inhibitors of S-adenosyl-L-homocysteine (AdoHcy) hydrolase was the elucidation of its mechanism of catalysis by Palmer and Abeles (J. Biol. Chem. 254, 1217–1226, 1979). This mechanism involves an NAD⁺-dependent oxidation (oxidative activity) of the 3′-hydroxyl group of AdoHcy followed by elimination of homocysteine (Hcy) to form 4′,5′-didehydro-3′-keto-Ado. Addition of water at the 5′-position (hydrolytic activity) of this tightly bound intermediate followed by an NADH-dependent reduction results in the formation of adenosine (Ado). Many inhibitors of this enzyme have been shown to serve as substrates [e.g., 9-(trans-2-trans-3-dihydroxycyclopent-4-en-1-yl)adenine, DHCeA)] for the oxidative activity of AdoHcy hydrolase, affording the 3′-keto-derivative (e.g., 3′-keto-DHCeA), which is tightly bound to the enzyme, and converting the enzyme from its active form (NAD⁺) to its inactive form (NADH) (Type I mechanism-based inhibitors; Wolfe and Borchardt, J. Med. Chem. 34, 1521–1530, 1991). More recently, substrates [e.g., (E)-5.,6′-didehydro-6′-deoxy-6′-fluorohomoadenosine, EDDFHA] for the hydrolytic activity of AdoHcy hydrolase have been identified by our laboratories. Identification of hydrolytic substrates affords a new strategy for the design of more potent and more specific inhibitors of AdoHcy hydrolase.