In vitro and in vivo Stability of the 2ζ2 Protein Complex of the Broad Host-Range Streptococcus pyogenes pSM19035 Addiction System (original) (raw)

Abstract

Streptococcus pyogenes pSM19035-encoded (10.7 kDa) and ζ (32.4 kDa) proteins are necessary to secure stable plasmid inheritance in bacteria, with ζ acting as toxin that kills plasmiddeprived cells and as an antitoxin that neutralises the activity of ζ. The and ζ proteins copurify as a stable complex that, according to analytical ultracentrifugation and gel filtration, exists as 2ζ2 heterotetramer in solution. Cocrystals of the 2ζ2 complex contain and ζ in 1:1 molar ratio. Unfolding studies monitoring circular dichroic and fluorescence changes show that the ζ protein has a significantly lower thermodynamic stability than the protein both in free state and in the complex. Proteolytic studies indicate that ζ protein is more stable in the the 2ζ2 complex than in the free state. In vivo studies reveal a short halflife of the antitoxin (~18min) and a long lifetime of the ζ toxin (>60min). When transcriptiontranslation of a plasmid containing the and ζ genes was inhibited, cell death was observed after a short lag phase that correlates with the disappearance of the protein from the background.

Published Online: 2005-06-01

Published in Print: 2002-11-13