Vol. 62, Issue 4, 795-805, October 2002

Kinetics and Crystal Structure of Catechol-O-Methyltransferase Complex with Co-Substrate and a Novel Inhibitor with Potential Therapeutic Application

Maria João Bonifácio, Margarida Archer, Maria L. Rodrigues, Pedro M. Matias, David A. Learmonth, Maria Arménia Carrondo, and Patrício Soares-da-Silva

Department of Research and Development, BIAL, S. Mamede do Coronado, Portugal (M.J.B., D.A.L., P.S.S.); Instituto de Tecnologia Química e Biológica-Universidade Nova de Lisboa, Oeiras, Portugal (M.A., M.L.R., P.M.M., M.A.C.); and Instituto de Biologia Experimental e Tecnológica, Oeiras, Portugal (M.A., M.L.R.)

Catechol-O-methyltransferase (COMT; E.C. 2.1.1.6) is a ubiquitous enzyme in nature that plays an important role in the metabolism of catechol neurotransmitters and xenobiotics. In particular, inactivation of drugs such as L-3,4-dihydroxyphenylalanine (L-DOPA) via O-methylation is of relevant pharmacological importance, because L-DOPA is currently the most effective drug used in the treatment of Parkinson's disease. This justified the interest in developing COMT inhibitors as potential adjuncts to L-DOPA therapy. The kinetics of inhibition by BIA 3-335 (1-[3,4-dihydroxy-5-nitrophenyl]-3-(N-3'-trifluormethylphenyl)-piperazine-1-propanone dihydrochloride) were characterized using recombinant rat soluble COMT. BIA 3-335 was found to act as a potent, reversible, tight-binding inhibitor of COMT with a K_i of 6.0 ± 1.6 nM and displaying a competitive inhibition toward the substrate binding site and uncompetitive inhibition toward the S-adenosyl-L-methionine (SAM) binding site. The 2.0-Å resolution crystal structure of COMT in complex with its cosubstrate SAM and a novel inhibitor BIA 3-335 shows the atomic interactions between the important residues at the active site and the inhibitor. This is the first report of a three-dimensional structure determination of COMT complexed with a potent, reversible, and tight-binding inhibitor that is expected to have therapeutic applications.