HicAB toxin–antitoxin complex fromEscherichia coli: expression and crystallization

Abstract

Toxin–antitoxin (TA) systems are widespread in both bacteria and archaea, where they enable cells to adapt to environmental cues. TA systems play crucial roles in various cellular processes, such as programmed cell death, cell growth, persistence and virulence. Here, two distinct forms of the type II toxin–antitoxin complex HicAB were identified and characterized inEscherichia coliK-12, and both were successfully overexpressed and purified. The two proposed forms, HicABLand HicABS, differed in the presence or absence of a seven-amino-acid segment at the N-terminus in the antitoxin HicB. The short form HicABSreadily crystallized under the conditions 0.1 MTris–HCl pH 8.0, 20%(w/v) PEG 6000, 0.2 Mammonium sulfate. The HicABScrystal diffracted and data were collected to 2.5 Å resolution. The crystal belonged to space groupI222 orI212121, with unit-cell parametersa= 67.04,b= 66.31,c= 120.78 Å. Matthews coefficient calculation suggested the presence of two molecules each of HicA and HicBSin the asymmetric unit, with a solvent content of 55.28% and a Matthews coefficient (VM) of 2.75 Å3 Da−1.