title: Functional insights into the Shigella type III needle tip IpaD in secretion control and cell contact.
abstract: Type III secretion apparatus (T3SA) are complex nanomachines that insert a translocation pore into the host cell membrane through which effector proteins are injected into the cytosol. In Shigella, the pore is inserted by a needle tip complex that also controls secretion. IpaD is the key protein that rules the composition of the tip complex before and upon cell contact or Congo red (CR) induction. However, how IpaD is involved in secretion control and translocon insertion remains not fully understood. Here, we report the phenotypic analysis of 20 10-amino acids deletion variants all along the coiled-coil and the central domains of IpaD (residues 131-332). Our results highlight three classes of T3S phenotype; (i) wild-type secretion, (ii) constitutive secretion of all classes of effectors, and (iii) constitutive secretion of translocators and early effectors, but not of late effectors. Our data also suggest that the composition of the tip complex defines both the T3SA inducibility state and late effectors secretion. Finally, we shed light on a new aspect regarding the contact of the needle tip with cell membrane by uncoupling the Shigella abilities to escape macrophage vacuole, and to insert the translocation pore or to invade non-phagocytic cells.
authors: Laboratoire de Bactériologie Moléculaire, Faculté de Médecine, Université Libre de Bruxelles, Route de Lennik, 808, 1070 Bruxelles, Belgium.
authors: Lionel
authors: L
authors: Schiavolin
authors: Alaeddine
authors: A
authors: Meghraoui
authors: Youness
authors: Y
authors: Cherradi
authors: Latéfa
authors: L
authors: Biskri
authors: Anne
authors: A
authors: Botteaux
authors: Abdelmounaaïm
authors: A
authors: Allaoui
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D008958:Models, Molecular; D021381:Protein Transport; D017384:Sequence Deletion; D012763:Shigella flexneri / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; C095770:IpaD protein, Shigella flexneri; C087447:ipaB protein, Shigella