Distinguishing Active Site Characteristics of Chlorite Dismutases with Their Cyanide Complexes
| Autor: | Gudrun S. Lukat-Rodgers, Jeffery A. Mayfield, Jennifer L. DuBois, Arianna I. Celis, Zachary Geeraerts, Megan Lorenz, Kenton R. Rodgers |
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| Rok vydání: | 2018 |
| Předmět: |
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Molecular 0301 basic medicine Hemeprotein Stereochemistry Cyanide Heme 010402 general chemistry 01 natural sciences Biochemistry Article 03 medical and health sciences chemistry.chemical_compound Perchlorate Bacterial Proteins Chlorides Catalytic Domain Chlorite Cyanides biology Active site Ligand (biochemistry) 0104 chemical sciences Turnover number Oxygen Klebsiella pneumoniae 030104 developmental biology chemistry biology.protein Oxidoreductases |
| Zdroj: | Biochemistry. 57:1501-1516 |
| ISSN: | 1520-4995 0006-2960 |
| DOI: | 10.1021/acs.biochem.7b01278 |
| Popis: | O(2)-evolving chlorite dismutases (Clds) efficiently convert chlorite (ClO(2)(−)) to O(2) and Cl(−). Dechloromonas aromatica Cld (DaCld) is a highly active chlorite-decomposing homopentameric enzyme, typical of Clds found in perchlorate and chlorate respiring bacteria. The Gram-negative, human pathogen Klebsiella pneumoniae contains a homodimeric Cld (KpCld) that also decomposes ClO(2)(−), albeit with a 10-fold lower activity and a lower turnover number compared to DaCld. The interactions between the distal pocket and heme ligand of the DaCld and KpCld active sites have been probed via kinetic, thermodynamic and spectroscopic behaviors of their cyanide complexes for insight into active site characteristics that are deterministic for chlorite decomposition. At 4.7 × 10(−9) M, the K(D) for KpCld–CN(−) is two orders of magnitude smaller than that of DaCld–CN(−) and indicates an affinity for CN(−) that is greater than that of most heme proteins. The difference in CN(−) affinity between Kp and DaClds is predominantly due to differences in k(off). The kinetics of cyanide binding to DaCld, DaCld(R183Q) and KpCld between pH 4 and 8.5 corroborate the importance of distal Arg183 and a pK(a) ~ 7 in stabilizing complexes of anionic ligands, including substrate. The Fe–C stretching and FeCN bending modes of DaCld–CN(−) (ν(Fe-C), 441 cm(−1); δ(FeCN), 396 cm(−1)) and KpCld–CN(−) (ν(Fe-C), 441 cm(−1); δ(FeCN), 356 cm(−1)) reveal differences in their FeCN angle, which suggest different distal pocket interactions with their bound cyanide. Conformational differences in their catalytic sites are also reported by the single ferrous KpCld carbonyl complex, which is in contrast to the two conformers observed for DaCld–CO. |
| Databáze: | OpenAIRE |
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