Structural insights into Pseudomonas aeruginosa Type six secretion system exported effector 8

Abstract Recent reports indicate the T ype s ix secretion system e xported effector 8 (Tse8) is a cytoactive effector secreted by the Type VI secretion system (T6SS) of the human pathogen Pseudomonas aeruginosa. The T6SS is a nanomachine that assembles inside of the bacteria and injects effectors/toxins into target cells, providing a fitness advantage over competing bacteria and facilitating host colonisation. Here we present the first crystal structure of Tse8, showing it conserves a putative catalytic triad Lys84-transSer162-Ser186 found among homologues. Furthermore, we measure the binding of phenylmethylsulfonyl fluoride (PMSF) to Tse8. Remarkably, we observed that PMSF binding is dependent on the putative catalytic residue Ser186, providing evidences of its nucleophilic reactivity. This work demonstrates that Tse8 belongs to the Amidase Signature (AS) superfamily. Furthermore, it highlights Tse8 similarity to two family members: the Stenotrophomonas maltophilia Peptide Amidase, and the Glutamyl-tRNAGln amidotransferase subunit A from Staphylococcus aureus.