Structural And Functional Insights Into PA0824-PA0821 Encoded By Pseudomonas Aeruginosa PAAR2 Cluster

The bacterial type Ⅵ secretion system(T6SS)secretes many toxic effectors to gain advantage in inter bacterial competition and for eukaryotic host infection.The cognate immunity proteins of these effectors protect bacteria from the virulence of their own effectors.The T6 SS injects its inner-needle Hcp tube,the sharpening tip complex consisting of Vgr G and PAAR(proline-alanine-alanine-arginine repeats)proteins,and toxic effectors into neighbouring cells.Its functions are largely determined by the activities of its delivered effectors.Five PAAR proteins were found in the Pseudomonas aeruginosa PAO1 genome,and three of them were reported to facilitate the delivery of various effectors.Four proteins are encoded in the less investigated P.aeruginosa PAAR2 cluster.The crystal structure of PA0821 is presented at 1.6 (?)resolution,and we proposed PA0821 to be an immunity.As PA0822 contains virus-type replication-repair nuclease(VRR-NUomain,we proposed PA0822 to be an an effector with nuclease activity.Through structure and sequence comparisons,we proposed PA0822-PA0821 to be a putative novel effector-immunity(E-I)pair.The role of PA0823 is still unknown.Through a large number of sequence comparisons,we found that it may be an N-terminal domain isolated from PA0822.We named the fusion protein of PA0823 and PA0822 as Tse V＿Fu and verified it through experiments.As a PAAR protein,the C-terminal of PA0824 interacts with Tse V＿Fu.We proposed that its function is to facilitate Tse V＿Fu to transport.