Effects of mutations in active site heme ligands on the spectroscopic and catalytic properties of SoxAX cytochromes.

Effects of mutations in active site heme ligands on the spectroscopic and catalytic properties of SoxAX cytochromes. J Inorg Biochem. 2016 Apr 15; Authors: Kilmartin JR, Bernhardt PV, Dhouib R, Hanson GR, Riley MJ, Kappler U Abstract By attaching a sulfur substrate to a conserved cysteine of the SoxYZ carrier protein SoxAX cytochromes initiate the reaction cycle of the Sox (sulfur oxidation) multienzyme complex, which is the major pathway for microbial reoxidation of sulfur compounds in the environment. Despite their important role in this process, the reaction mechanism of the SoxAX cytochromes has not been fully elucidated. Here we report the effects of several active site mutations on the spectroscopic and enzymatic properties of the type II SoxAX protein from Starkeya novella, which in addition to two heme groups also contains a Cu redox centre. All substituted proteins contained these redox centres except for His231Ala which was unable to bind Cu(II). Substitution of the SoxA active site heme cysteine ligand with histidine resulted in increased microheterogeneity around the SoxA heme as determined by CW-EPR, while a SnSoxAX(C236A) substituted protein revealed a completely new, nitrogenous SoxA heme ligand. The same novel ligand was present in SnSoxAX(H231A) CW-EPR spectra, the first time that a ligand switch of the SoxA heme involving a nearby amino acid has been demonstrated. Kinetically, SnSoxAX(C236A) and SnSoxAX(C236H) showe...
Source: Journal of Inorganic Biochemistry - Category: Biochemistry Authors: Tags: J Inorg Biochem Source Type: research