3-DIMENSIONAL STRUCTURE OF MICROBIAL 2-HYDROXYL-6-OXO-6-PHENYLHEXA-2,4-DIENOIC ACID (HPDA) HYDROLASE (BPHD ENZYME) FROM RHODOCOCCUS SP. STRAIN RHA1, IN THE PCB DEGRADATION PATHWAY

The three-dimensional structure of an enzyme, 2-hydroxyl-6-oxo-6-pheny lhexa-2,4-dienoic acid (HPDA) hydrolase (conventionally called BphD) f rom Rhodococcus sp. strain RHA1 has been solved by X-ray crystal struc ture analysis. This enzyme hydrolyzes one of the highly reactive inter mediates, the meta cleavage product of the reaction catalyzed by 2,3-d ihydroxybiphenyl dioxygenase, in the metabolic pathway degrading biphe nyl compounds including the notorious environmental pollutant PCBs (po lychlorinated biphenyls). By virtue of this and several other enzymes, the biphenyl compounds including PCBs are finally introduced into til e tricarboxylic acid cycle. The BphD enzyme is an oligomeric enzyme ma de up of eight identical subunits each of 285 amino acid residues. The subunit consists of two domains, alpha/beta domain and alpha domain, between which the active site is located.