Crystal structure of dihydropyrimidinase from Pseudomonas aeruginosa PAO1: Insights into the molecular basis of formation of a dimer

Dihydropyrimidinase, a tetrameric metalloenzyme, is a member of the cyclic amidohydrolase family, which also includes allantoinase, dihydroorotase, hydantoinase, and imidase. In this paper, we report the crystal structure of dihydropyrimidinase from Pseudomonas aeruginosa PAO1 at 2.1 A resolution. The structure of P. aeruginosa dihydropyrimidinase reveals a classic (β/α)8-barrel structure core embedding the catalytic dimetal center and a β-sandwich domain, which is commonly found in the architecture of dihydropyrimidinases. In contrast to all dihydropyrimidinases, P. aeruginosa dihydropyrimidinase forms a dimer, rather than a tetramer, both in the crystalline state and in the solution. Basing on sequence analysis and structural comparison of the C-terminal region and the dimer–dimer interface between P. aeruginosa dihydropyrimidinase and Thermus sp. dihydropyrimidinase, we propose a working model to explain why this enzyme cannot be a tetramer.