Solution structure of the phosphatidylinositol 3-phosphate binding domain from the Legionella effector SetA
Legionella pneumophila is a facultative intracellular pathogen that causes Legionnaires disease or Pontiac fever in humans upon accidental inhalation of Legionella-contaminated aerosols. During infection, L. pneumophila secretes more than 300 effectors into the host for the biogenesis of a replication-permissive niche, known as the Legionella containing vacuole (LCV). Among these, a large number of effectors harbor protein domains that recognize specific phosphoinositide (PI) lipids and mediate the anchoring of these effectors to the surface of LCV or other host membrane-bound organelles. The Legionella effector SetA contains a unique C-terminal domain (SetA-CTD) that has been shown to specifically bind with phosphatidylinositol-3-phosphate (PI(3)P) and target SetA to endosomes and LCVs. Here, we report the NMR solution structure of SetA-CTD, which mainly comprises a four -helix bundle. The structure reveals a basic pocket at one end of the -helix bundle for PI(3)P binding and two hydrophobic loops for membrane insertion. Mutations of key residues involved in lipid binding result in the loss of SetA in membrane association and endosomal localization. Structural comparison with other PI(3)P-binding domains highlights a general theme applied by multiple families of phosphoinositide-binding domains across species.