Abstract
Legionella pneumophila, a causative agent of pneumonia, utilizes the Type 4B secretion (T4BS) system to translocate over 300 effectors into the host cell during infection. T4BS systems are encoded by a large gene cluster termed dot/icm, three components of which, DotL, DotM, and DotN, form the “coupling complex”, which serves as a platform for recruitment of effector proteins. One class of effectors includes proteins containing Glu-rich/E-block sequences at their C terminus. However, the protein or region of the coupling complex mediating recruitment of such effectors is unknown. Here we present the crystal structure of DotM. This all alpha-helical structure exhibits patches of positively charged residues. We show that these regions form binding sites for acidic Glu-rich peptides and that mutants targeting these patches are defective in vivo in the translocation of acidic Glu-rich motif-containing effectors. We conclude that DotM forms the interacting surface for recruitment of acidic Glu-rich motif-containing Legionella effectors.
Highlights
Legionella pneumophila, a causative agent of pneumonia, utilizes the Type 4B secretion (T4BS) system to translocate over 300 effectors into the host cell during infection
In this study, we investigate the role of DotM, until now an enigmatic member of the T4BS secretion coupling complex
Our results suggest that DotM’s cytoplasmic domain is capable of binding directly another subgroup of Legionella effectors that contain acidic Glu-rich motifs at their C terminus
Summary
Legionella pneumophila, a causative agent of pneumonia, utilizes the Type 4B secretion (T4BS) system to translocate over 300 effectors into the host cell during infection. The infection mechanism by which Legionella recruits and manipulates transport of the phagosome involves over 300 bacterial genes encoding different proteins, called effectors, that are secreted from the bacteria to the host cell[5]. T4S systems are comprised of protein complexes that assemble into a machine that traverses the bacterial inner membrane and cell envelope These systems are usually used to transport DNA molecules from a donor cell to a recipient cell during conjugation, to take up macromolecules from the environment during transformation, or to transport effector proteins from the bacterium to a host cell during infection. The coupling protein/complex includes an inner membrane ATPase belonging to the VirD4 family of proteins[14,15,16]
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