Title
Roles of Conserved Residues of the Glycine Oxidase GoxA in Controlling Activity, Cooperativity, Subunit Composition, and Cysteine Tryptophylquinone Biosynthesis
Funding Source
National Institute of General Medical Sciences, National Institutes of Health
Grant Number
R37GM41574
Department
Department of Chemistry
Document Type
Article
Publication Date
10-28-2016
Abstract
GoxA is a glycine oxidase that possesses a cysteine tryptophylquinone (CTQ) cofactor that is formed by posttranslational modifications that are catalyzed by a modifying enzyme GoxB. It is the second known tryptophylquinone enzyme to function as an oxidase, the other being the lysine ô-oxidase, LodA. All other enzymes containing CTQ or tryptophan tryptophylquinone (TTQ) cofactors are dehydrogenases. Kinetic analysis of GoxA revealed allosteric cooperativity for its glycine substrate, but not O2 . This is the first CTQ- or TTQ-dependent enzyme to exhibit cooperativity. Here, we show that cooperativity and homodimer stabilization are strongly dependent on the presence of Phe-237. Conversion of this residue, which is a Tyr in LodA, to Tyr or Ala eliminates the cooperativity and destabilizes the dimer. These mutations also significantly affect the kcat and Km values for the substrates. On the basis of structural and modeling studies, a mechanism by which Phe-237 exerts this influence is presented. Two active site residues, Asp-547 and His-466, were also examined and shown by site-directed mutagenesis to be critical for CTQ biogenesis. This result is compared with the results of similar studies of mutagenesis of structurally conserved residues of other tryptophylquinone enzymes. These results provide insight into the roles of specific active-site residues in catalysis and CTQ biogenesis, as well as describing an interesting mechanism by which a single residue can dictate whether or not an enzyme exhibits cooperative allosteric behavior toward a substrate. ©
Recommended Citation
Sehanobish, E.; Williamson, Heather R.; and Davidson, V. L., "Roles of Conserved Residues of the Glycine Oxidase GoxA in Controlling Activity, Cooperativity, Subunit Composition, and Cysteine Tryptophylquinone Biosynthesis" (2016). Faculty and Staff Publications. 160.
https://digitalcommons.xula.edu/fac_pub/160
Comments
DOI: 10.1074/jbc.M116.741835
PubMed ID: 27637328
Funding text
This research was supported by internal funds from the Burnett School of Biomedical Sciences and in part by the NIGMS, National Institutes of Health Grant R37GM41574 (to V. L. D.). The authors declare that they have no conflicts of interest with the contents of this article. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.