Crystallization and preliminary X-ray analysis of a bifunctional enzyme: HHDD isomerase/OPET decarboxylase from Escherichia coli

A bifunctional enzyme, 2-hydroxyhepta-2,4,-diene-l,7-dioate isomerase/5-oxopent-3-ene-1,2,5-tricarboxylate decarboxylase from the homoprotocatechaute (HPC) degradative pathway of Escherichia coli has been crystallized, using polyethylene glycol as a precipitant. The enzyme, of molecular weight 44 514 Da forms crystals belonging to the orthorhombic space group P2₁2₁2₁ with cell dimensions a = 106, b = 127 and c = 139 Å. The crystals diffract to at least 2.2 Å resolution using synchrotron radiation. A complete native data set has been collected to 3.3 Å resolution. The Matthews number calculated for a single molecule in the asymmetric unit is outside the normally acceptable limits and the aggregation state of the molecules in the crystal was investigated using self-rotation function studies, the results show features which are consistent with a tetramer in the asymmetric unit, giving a V_m value of 2.7 Å³ Da^-1.