W0178

Degradation of PCBs: Structural Features That Permit or Prevent Dioxygenase Cleavage of 4-Substituted Catechols. David B. Neau¹, Halim Maaroufi², Lindsay D. Eltis², and Jeffrey T. Bolin¹, Markey Center for Structural Biology, Dept. of Biological Sciences, Purdue Univ., W Lafayette, IN 47907-2054, USA; ²Depts. of Microbiology and Biochemistry, Univ. British Columbia, Vancouver, BC, V6T 1Z3, Canada.

Failures in the processing of PCBs and PCB metabolites by bacterial bph pathways limit prospects for bioremediation of these notorious pollutants. One cause of failure is the generation of 4-substituted catechols, which are not processed by key ring-cleaving dioxygenases. We define a structural basis for this failure by determining and comparing structures of ring-cleaving dioxygenases that succeed and fail.

DoxG_C18 is a 1,2-dihydroxynaphthalene dioxygenase from Pseudomonas strain C18. DHDB_LB400 is the homologous 2,3-dihydroxybiphenyl 1,2-dioxygenase from the bph pathway of Burkholderia strain LB400. DoxG cleaves 3,4-dihydroxybiphenyl (3,4-DHB = 4-phenylcatechol), whereas DHDB_LB400 does not do so.

We determined high resolution (1.5 to 1.9 Å) structures for DoxG and its binary complexes with at least four substrates, including 3,4-DHB, 2,3-DHB, 4-methylcatechol, and 1,2-dihydroxynaphthalene. By comparisons to previously determined substrate complexes of DHDB_LB400, these results reveal variations in enzyme:substrate interactions and dynamic features of enzyme structure that correlate with competency for cleavage of 4-substituted catechols and, presumably, related PCB metabolites.

Supported by NIH (R01-GM52381 and T32-GM08296) and NSERC (STP01923182), and various agencies that support BioCARs and SBC at the Advanced Photon Source.