Structural studies on extradiol dioxygenases: Strategies for improved bioremediation of PCBs

Mustafa Koksal, Purdue University

Abstract

Bioremediation has emerged as a possible alternative to other non-biological methods to eliminate polychlorinated biphenyls (PCBs). However, there are limitations due to inabilities of the microorganisms that may be used in this process. 2,3-dihydroxybiphenyl-1,2-dioxygenase (DHBD), which cleaves the aromatic ring of PCBs, is one of the key enzymes in the biodegradation pathway, determining the ability of an organism to degrade a wide variety of PCBs. Burkholderia xenovorans strain LB400 is a potential candidate organism for bioremediation applications, however, DHBDLB400 suffers from substrate-facilitated suicide inactivation, poor catalytic activity and low substrate specificity for some PCB congeners. Supplementation of the organism with DHBD variants from other pathways was considered as a powerful strategy to improve the capacity of this organism. Structures of four enzymes were determined and analyzed to assess their potential in improving the bioremediation process: THBD RW1, an enzyme that is relatively more resistant to inactivation; DoxG-SMA2, a directed evolution mutant more active than DHBDLB400 and its wild-type against certain metabolites; DHBDP6-I and -III, two enzymes with complementary substrate specificities, which have higher specificity than DHBDLB400 for certain monochlorinated metabolites. Their structural analysis presented new opportunities for improvement of the bioremediation process by recruiting and improving these enzymes through selected or directed modifications.

Degree

Ph.D.

Advisors

Bolin, Purdue University.

Subject Area

Biochemistry|Biophysics

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