Structure and mechanism of benzoylformate decarboxylase, a thiamin dtthosphate-dependent enzyme

Benzoylformate decarboxylase (BFD) is a thiamin diphosphate (TDP)-requiring enzyme found in the mandelate pathway in Pseydomonas putida. Its crystal structure has recently been solved at 1.6A resolution and refined to an R-factor of 15.0% (free R=18.5%). The overall architecture of BFD resembles that of other family members, especially in the cofactor binding site. Surprisingly, even though BFD catalyzes the same fundamental chemical reaction as pyruvate decarboxylase, there is no conservation of active site residues not directly bound to the cofactor. This suggests that cofactor chemistry, the nature of reaction intermediates and architectural considerations relating to the protein fold have been dominant forces in the evolution of TDP-dependent enzymes. Site-directed mutagenesis experiments have recently been initiated to try to elucidate the catalytic mechanism. (Supported by N1H Grants GM-40570 and GM 26788, DRG-1194 of the Cancer Research Fund of the Damon Runyon-Walter Winchell Foundation and the Lucille P. Markey Charitable Trust.).