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Journal of Bacteriology, February 2007, p. 1266-1278, Vol. 189, No. 4
0021-9193/07/$08.00+0     doi:10.1128/JB.01130-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The yefM-yoeB Toxin-Antitoxin Systems of Escherichia coli and Streptococcus pneumoniae: Functional and Structural Correlation ^,

Centro de Investigaciones Biológicas, CSIC, Madrid, Spain,¹ Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Tel Aviv 69978, Israel,² Department of Biotechnology, Malaysia University of Science and Technology, Petaling Jaya, Malaysia³

Received 27 July 2006/ Accepted 16 October 2006

Toxin-antitoxin loci belonging to the yefM-yoeB family are located in the chromosome or in some plasmids of several bacteria. We cloned the yefM-yoeB locus of Streptococcus pneumoniae, and these genes encode bona fide antitoxin (YefM_Spn) and toxin (YoeB_Spn) products. We showed that overproduction of YoeB_Spn is toxic to Escherichia coli cells, leading to severe inhibition of cell growth and to a reduction in cell viability; this toxicity was more pronounced in an E. coli B strain than in two E. coli K-12 strains. The YoeB_Spn-mediated toxicity could be reversed by the cognate antitoxin, YefM_Spn, but not by overproduction of the E. coli YefM antitoxin. The pneumococcal proteins were purified and were shown to interact with each other both in vitro and in vivo. Far-UV circular dichroism analyses indicated that the pneumococcal antitoxin was partially, but not totally, unfolded and was different than its E. coli counterpart. Molecular modeling showed that the toxins belonging to the family were homologous, whereas the antitoxins appeared to be specifically designed for each bacterial locus; thus, the toxin-antitoxin interactions were adapted to the different bacterial environmental conditions. Both structural features, folding and the molecular modeled structure, could explain the lack of cross-complementation between the pneumococcal and E. coli antitoxins.

Published ahead of print on 27 October 2006.

Dedicated to Martine Thilly-Couturier, a retired pioneer in toxins-antitoxins and a continuous friend.

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