@article{mccombs_moreno-chicano_carey_franzen_hough_ghiladi_2017, title={Interaction of Azole-Based Environmental Pollutants with the Coelomic Hemoglobin from Amphitrite ornata: A Molecular Basis for Toxicity}, volume={56}, ISSN={0006-2960 1520-4995}, url={http://dx.doi.org/10.1021/acs.biochem.7b00041}, DOI={10.1021/acs.biochem.7b00041}, abstractNote={The toxicities of azole pollutants that have widespread agricultural and industrial uses are either poorly understood or unknown, particularly with respect to how infaunal organisms are impacted by this class of persistent organic pollutant. To identify a molecular basis by which azole compounds may have unforeseen toxicity on marine annelids, we examine here their impact on the multifunctional dehaloperoxidase (DHP) hemoglobin from the terebellid polychaete Amphitrite ornata. Ultraviolet-visible and resonance Raman spectroscopic studies showed an increase in the six-coordinate low-spin heme population in DHP isoenzyme B upon binding of imidazole, benzotriazole, and benzimidazole (Kd values of 52, 82, and 110 μM, respectively), suggestive of their direct binding to the heme-Fe. Accordingly, atomic-resolution X-ray crystal structures, supported by computational studies, of the DHP B complexes of benzotriazole (1.14 Å), benzimidazole (1.08 Å), imidazole (1.08 Å), and indazole (1.12 Å) revealed two ligand binding motifs, one with direct ligand binding to the heme-Fe, and another in which the ligand binds in the hydrophobic distal pocket without coordinating the heme-Fe. Taken together, the results demonstrate a new mechanism by which azole pollutants can potentially disrupt hemoglobin function, thereby improving our understanding of their impact on infaunal organisms in marine and aquatic environments.}, number={17}, journal={Biochemistry}, publisher={American Chemical Society (ACS)}, author={McCombs, Nikolette L. and Moreno-Chicano, Tadeo and Carey, Leiah M. and Franzen, Stefan and Hough, Michael A. and Ghiladi, Reza A.}, year={2017}, month={Apr}, pages={2294–2303} }
 @article{mccombs_smirnova_ghiladi_2017, title={Oxidation of pyrrole by dehaloperoxidase-hemoglobin: chemoenzymatic synthesis of pyrrolin-2-ones}, volume={7}, ISSN={["2044-4761"]}, url={http://dx.doi.org/10.1039/c7cy00781g}, DOI={10.1039/c7cy00781g}, abstractNote={The use of oxidoreductases as biocatalysts in the syntheses of functionalized, monomeric pyrroles has been a challenge owing to, among a number of factors, undesired polypyrrole formation. Here, we have investigated the ability of dehaloperoxidase (DHP), the coelomic hemoglobin from the terebellid polychaete Amphitrite ornata, to catalyze the H2O2-dependent oxidation of pyrroles as a new class of substrate for this enzyme. Substrate oxidation was observed for all compounds employed (pyrrole, N-methylpyrrole, 2-methylpyrrole, 3-methylpyrrole and 2,5-dimethylpyrrole) under both aerobic and anaerobic conditions. Using pyrrole as a representative substrate, only a single oxidation product, 4-pyrrolin-2-one, was observed, and notably without formation of polypyrrole. Reactivity could be initiated from all three biologically relevant oxidation states for this catalytic globin: ferric, ferrous and oxyferrous. Isotope labeling studies determined that the O-atom incorporated into the 4-pyrrolin-2-one product was derived exclusively from H2O2, indicative of a peroxygenase mechanism. Consistent with this observation, single- and double-mixing stopped-flow UV-visible spectroscopic studies supported Compound I, but not Compounds ES or II, as the catalytically-relevant ferryl intermediate involved in pyrrole oxidation. Electrophilic addition of the ferryl oxygen to pyrrole is proposed as the mechanism of O-atom transfer. The results demonstrate the breadth of chemical reactivity afforded by dehaloperoxidase, and provide further evidence for establishing DHP as a multifunctional globin with practical applications as a biocatalyst.}, number={14}, journal={CATALYSIS SCIENCE & TECHNOLOGY}, author={McCombs, Nikolette L. and Smirnova, Tatyana and Ghiladi, Reza A.}, year={2017}, month={Jul}, pages={3104–3118} }