Energetics of MazG unfolding in correlation with its structural features.

MazG is a homodimeric alpha-helical protein that belongs to the superfamily of all-alpha NTP pyrophosphatases. Its function has been connected to the regulation of the toxin-antitoxin module mazEF, implicated in programmed growth arrest/cell death of Escherichia coli cells under conditions of amino acid starvation. The goal of the first detailed biophysical study of a member of the all-alpha NTP pyrophosphatase superfamily, presented here, is to improve molecular understanding of the unfolding of this type of proteins.

MazG -- a regulator of programmed cell death in Escherichia coli.

We have previously reported that mazEF, the first regulatable chromosomal 'addiction module' located on the Escherichia coli chromosome, downstream from the relA gene, plays a crucial role in the programmed cell death in bacteria under stressful conditions. It consists of a pair of genes encoding a stable toxin, MazF, and MazE, a labile antitoxin interacting with MazF to form a complex. The cellular target of MazF toxin was recently described to be cellular mRNA, which is degraded by this toxin.

Energetics of structural transitions of the addiction antitoxin MazE: is a programmed bacterial cell death dependent on the intrinsically flexible nature of the antitoxins?

The Escherichia coli mazEF addiction module plays a crucial role in the cell death program that is triggered under various stress conditions. It codes for the toxin MazF and the antitoxin MazE, which interferes with the lethal action of the toxin. To better understand the role of various conformations of MazE in bacterial life, its order-disorder transitions were monitored by differential scanning calorimetry, spectropolarimetry, and fluorimetry.

Crystal structure of the intrinsically flexible addiction antidote MazE.

A specific camel VHH (variable domain of dromedary heavy chain antibody) fragment was used to crystallize the intrinsically flexible addiction antidote MazE. Only 45% of the polypeptide chain is found ordered in the crystal. The MazE monomer consisting of two beta-hairpins connected by a short alpha-helix has no hydrophobic core on its own and represents only one half of a typical protein domain.

Recognition of the intrinsically flexible addiction antidote MazE by a dromedary single domain antibody fragment. Structure, thermodynamics of binding, stability, and influence on interactions with DNA.

The Escherichia coli mazEF operon defines a chromosomal addiction module that programs cell death under various stress conditions. It encodes the toxic and long-lived MazF and the labile antidote MazE. The denaturation of MazE is a two-state reversible dimer-monomer transition.