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Role of glutathione in buffering excess intracellular copper in Streptococcus pyogenes.

Stewart, Louisa J. and Ong, Cheryl-lynn Y. and Zhang, May M. and Brouwer, Stephan and McIntyre, Liam and Davies, Mark R. and Walker, Mark J. and McEwan, Alastair G. and Waldron, Kevin J. and Djoko, Karrera Y. (2020) 'Role of glutathione in buffering excess intracellular copper in Streptococcus pyogenes.', mBio., 11 (6). e02804-20.


Copper (Cu) is an essential metal for bacterial physiology but in excess it is bacteriotoxic. To limit Cu levels in the cytoplasm, most bacteria possess a transcriptionally responsive system for Cu export. In the Gram-positive human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]), this system is encoded by the copYAZ operon. This study demonstrates that although the site of GAS infection represents a Cu-rich environment, inactivation of the copA Cu efflux gene does not reduce virulence in a mouse model of invasive disease. In vitro, Cu treatment leads to multiple observable phenotypes, including defects in growth and viability, decreased fermentation, inhibition of glyceraldehyde-3-phosphate dehydrogenase (GapA) activity, and misregulation of metal homeostasis, likely as a consequence of mismetalation of noncognate metal-binding sites by Cu. Surprisingly, the onset of these effects is delayed by ∼4 h even though expression of copZ is upregulated immediately upon exposure to Cu. Further biochemical investigations show that the onset of all phenotypes coincides with depletion of intracellular glutathione (GSH). Supplementation with extracellular GSH replenishes the intracellular pool of this thiol and suppresses all the observable effects of Cu treatment. These results indicate that GSH buffers excess intracellular Cu when the transcriptionally responsive Cu export system is overwhelmed. Thus, while the copYAZ operon is responsible for Cu homeostasis, GSH has a role in Cu tolerance and allows bacteria to maintain metabolism even in the presence of an excess of this metal ion.

Item Type:Article
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Publisher statement:Copyright © 2020 Stewart et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.
Date accepted:23 October 2020
Date deposited:08 December 2020
Date of first online publication:01 December 2020
Date first made open access:08 December 2020

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