Zn is known to have antibacterial properties, although the mechanism by which it acts was unknown. Here, the authors have found that ZnII competes with MnII for binding to the Streptococcus pneumoniae protein PsaA, a solute-binding protein that transports MnII into the cell to manage oxidative stress, among other functions. Although ZnII showed lower affinity for PsaA than MnII, the complex formed by ZnII and PsaA was more thermally stable. Furthermore, increasing the ZnII/MnII ratio, which would decrease MnII uptake, led to inhibition of S. pneumoniae growth in vitro owing to increased susceptibility to oxidative stress, as well as increased susceptibility to killing by polymorphonuclear leukocytes. Consistent with this, mice infected with S. pneumoniae showed a significant increase in ZnII levels compared with controls in tissue samples collected 48 hours post-infection. So, it seems that ZnII is toxic to S. pneumoniae because it inhibits MnII uptake.
ORIGINAL RESEARCH PAPER
McDevitt, C. A. et al. A molecular mechanism for bacterial susceptibility to zinc. PLoS Pathog. 7, e1002357 (2011)Article
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David, R. Why zinc is bad for bacteria. Nat Rev Microbiol 10, 4 (2012). https://doi.org/10.1038/nrmicro2726