Structural and Functional Study of the <i>Klebsiella pneumoniae</i> VapBC Toxin–Antitoxin System, Including the Development of an Inhibitor That Activates VapC

Abstract

<i>Klebsiella pneumoniae</i> is one of the most critical opportunistic pathogens. TA systems are promising drug targets because they are related to the survival of bacterial pathogens. However, structural information on TA systems in <i>K. pneumoniae</i> remains lacking; therefore, it is necessary to explore this information for the development of antibacterial agents. Here, we present the first crystal structure of the VapBC complex from <i>K. pneumoniae</i> at a resolution of 2.00 Å. We determined the toxin inhibitory mechanism of the VapB antitoxin through an Mg²⁺ switch, in which Mg²⁺ is displaced by R79 of VapB. This inhibitory mechanism of the active site is a novel finding and the first to be identified in a bacterial TA system. Furthermore, inhibitors, including peptides and small molecules, that activate the VapC toxin were discovered and investigated. These inhibitors can act as antimicrobial agents by disrupting the VapBC complex and activating VapC. Our comprehensive investigation of the <i>K. pneumoniae</i> VapBC system will help elucidate an unsolved conundrum in VapBC systems and develop potential antimicrobial agents.