SHEIDA (S) HEDAYAT<sup>1

1</sup>Department of infection, immunity and cardiovascular disease, Medical School, University of Sheffield, Sheffield, United Kingdom (UK)

Burkholderia cenocepacia has received increasing attention in recent years due to its pathogenicity in immunocompromised patients and CF patients.The type VI secretion system (T6SS) as a novel type of protein secretion system is present in Burkholderia cenocepacia and may play a role in its virulence. VgrG (TssI) is one of 13 core components of the T6SS machine but can also act as an effector.Two putative effector proteins with an additional domain at C-terminus with phospholipase A1 activity (PLA) are TssI BCAS0667 and TagD (BCAL1296). Downstream of BCAL1296 and BCAS0667 are genes encoding proteins with ankyrin-repeat domains (BCAL1297 and BCAS0666, respectively) that may serve as immunity proteins for the BCAL1296- and BCAS0667-encoded proteins. One of the aims of this project is to determine whether the putative accessory proteins BCAL1297 and BCAS0666 as putative immunity proteins interact with their corresponding effector proteins with phospholipase activity.In this project, the bacterial adenylate cyclase two-hybrid system (BACTH)and pull-down assay were used to investigate protein-protein interactions between BCAS0667 (evolved TssI) and protein BCAS0666, and between BCAL1296 (evolved TagD) and BCAL1297. The result of the two-hybrid and pull down analysis suggests that there are interactions between the two T6SS PLA effector proteins and the putative PLA accessory proteins. Therefore, the results support the idea that BCAS0666 and BCAL1297 are likely to be accessory proteins with a putative anti-toxin role for effectors BCAS0667 and BCAL1296, respectively.This insight suggests an opportunity for development an anti-bacterial therapeutic agent that targets T6SS effector immunity proteins that may benefit CF patients suffering from B. cenocpacia infections.