Crystallization and preliminary crystallographic characterization of catechol-O-methyltransferase in complex with its cosubstrate and an inhibitor

Catechol-O-methyltransferase (COMT) is involved in the metabolism of catech olamines, catechol steroids and xenobiotic catechols. A precise knowledge o f the enzyme-inhibitor structural interactions could help in the design of better inhibitors. Soluble rat COMT was expressed in Escherichia coli and t he recombinant protein was crystallized with a new tight-binding inhibitor, BIA 3-335 [1-(3,4-dihydroxy-5-nitrophenyl)-3-(n-3'-triuoromethylphenyl)pip erazine-1-propanone dihydrochloride]. The crystals were obtained by the sit ting-drop vapour-diffusion method using PEG 6K as a precipitant. These crys tals diffracted to better than 1.9 Angstrom and belong to the trigonal spac e group P3(2)21. The unit-cell parameters for the crystal measured at room temperature were a = b = 51.5, c = 168.3 Angstrom; each shrank by about 1 A ngstrom on freezing.