Title
Coordination Chemistry Controls the Thiol Oxidase Activity of the B12 Trafficking Protein CblC
Author
Zhu Li, Aranganathan Shanmuganathan, Markus Ruetz, Kazuhiro Yamada, Nicholas A Lesniak, Bernhard Kraeutler, Thomas C Brunold, Markos Koutmos, Ruma Banerjee
Year
2017
Journal
The Journal of Biological Chemistry
Abstract
The cobalamin or B12 cofactor supports sulfur and one-carbon metabolism and the catabolism of odd-chain fatty acids, branched-chain amino acids and cholesterol. CblC is a B12 processing enzyme involved in an early cytoplasmic step in the cofactor trafficking pathway. It catalyzes the glutathione (GSH)-dependent dealkylation of alkylcobalamins and the reductive decyanation of cyanocobalamin. CblC from Caenorhabdiitis elegans (ceCblC) also exhibits a robust thiol oxidase activity converting reduced GSH to oxidized GSSG with concomitant scrubbing of ambient dissolved O2. The mechanism of thiol oxidation catalyzed by ceCblC is not known. In this study, we demonstrate that novel coordination chemistry accessible to ceCblC-bound cobalamin, supports its thiol oxidase activity via a glutathionyl-cobalamin intermediate. Deglutathionylation of glutathionyl-cobalamin by a second molecule of GSH yields GSSG. The crystal structure of ceCblC provides insights into how architectural differences at the α- and β-faces of cobalamin promote the thiol oxidase activity of ceCblC but mute it in wild-type human CblC. The R161G and R161Q mutations in human CblC unmask its latent thiol oxidase activity and are correlated with increased cellular oxidative stress disease. In summary, we have uncovered key architectural features in the cobalamin-binding pocket that support unusual cob(II)alamin coordination chemistry and enable the thiol oxidase activity of ceCblC.
Instrument
J-715
Keywords
Magnetic circular dichroism, Coordination chemistry, Ligand binding, Biochemistry