Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada
Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Tahmid M Tashin
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada
Nathan P Bullen
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada
Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Andrew G McArthur
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada; David Braley Centre for Antibiotic Discovery, McMaster University, Hamilton, Canada
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Canada; David Braley Centre for Antibiotic Discovery, McMaster University, Hamilton, Canada
Type VI secretion systems (T6SSs) deliver antibacterial effector proteins between neighboring bacteria. Many effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across target cell membranes. However, the distribution of these TMD-containing effectors remains unknown. Here, we discover prePAAR, a conserved motif found in over 6000 putative TMD-containing effectors encoded predominantly by 15 genera of Proteobacteria. Based on differing numbers of TMDs, effectors group into two distinct classes that both require a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR residues mediate effector-VgrG spike interactions. Taken together, our findings reveal mechanisms of chaperone-mediated stabilization and secretion of two distinct families of T6SS membrane protein effectors.
