Crystal structure of the YoeBSa1-YefMSa1 complex from Staphylococcus aureus.

ABSTRACT

Toxin-antitoxin (TA) systems are ubiquitously found in bacteria and are related to cell maintenance and survival under environmental stresses such as heat shock, nutrient starvation, and antibiotic treatment. Here, we report for the first time the crystal structure of the Staphylococcus aureus TA complex YoeBSa1-YefMSa1 at a resolution of 1.7 Å. This structure reveals a heterotetramer with a 22 stoichiometry between YoeBSa1 and YefMSa1. The N-terminal regions of the YefMSa1 antitoxin form a homodimer characteristic of a hydrophobic core, and the C-terminal extended region of each YefMSa1 protomer makes contact with each YoeBSa1 monomer. The binding stoichiometry of YoeBSa1 and YefMSa1 is different from that of YoeB and YefM of E. coli (YoeBEc and YefMEc), which is the only structural homologue among YoeB-YefM families; however, the structures of individual YoeBSa1 and YefMSa1 subunits in the complex are highly similar to the corresponding structures in E. coli. In addition, docking simulation with a minimal RNA substrate provides structural insight into the guanosine specificity of YoeBSa1 for cleavage in the active site, which is distinct from the specificity of YoeBEc for adenosine rather than guanosine. Given the previous finding that YoeBSa1 exhibits fatal toxicity without inducing persister cells, the structure of the YoeBSa1-YefMSa1 complex will contribute to the design of a new category of anti-staphylococcal agents that disrupt the YoeBSa1-YefMSa1 complex and increase YoeBSa1 toxicity.