title: Deoxycholate interacts with IpaD of Shigella flexneri in inducing the recruitment of IpaB to the type III secretion apparatus needle tip.
abstract: Type III secretion (TTS) is an essential virulence function for Shigella flexneri that delivers effector proteins that are responsible for bacterial invasion of intestinal epithelial cells. The Shigella TTS apparatus (TTSA) consists of a basal body that spans the bacterial inner and outer membranes and a needle exposed at the pathogen surface. At the distal end of the needle is a "tip complex" composed of invasion plasmid antigen D (IpaD). IpaD not only regulates TTS, but is required for the recruitment and stable association of the translocator protein IpaB at the TTSA needle tip in the presence of deoxycholate or other bile salts. This phenomenon is not accompanied by induction of TTS or the recruitment of IpaC to the Shigella surface. We now show that IpaD specifically binds fluorescein-labeled deoxycholate and, based on energy transfer measurements and docking simulations, this interaction appears to occur where the N-terminal domain of IpaD meets its central coiled-coil, a region that may also be involved in needle-tip interactions. TTS is initiated as a series of distinct steps and that small molecules present in the bacterial milieu are capable of inducing the first step of TSS through interactions with the needle tip protein IpaD. Furthermore, the amino acids proposed to be important for deoxycholate binding by IpaD appear to have significant roles in regulating tip complex composition and pathogen entry into host cells.
authors.affiliation: Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA.
authors.forename: Kenneth F
authors.initials: KF
authors.lastname: Stensrud
authors.forename: Philip R
authors.initials: PR
authors.lastname: Adam
authors.forename: Cassandra D
authors.initials: CD
authors.lastname: La Mar
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Olive
authors.forename: Gerald H
authors.initials: GH
authors.lastname: Lushington
authors.forename: Raghavi
authors.initials: R
authors.lastname: Sudharsan
authors.forename: Naomi L
authors.initials: NL
authors.lastname: Shelton
authors.forename: Richard S
authors.initials: RS
authors.lastname: Givens
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Picking
authors.forename: William D
authors.initials: WD
authors.lastname: Picking
mesh_terms: D000942:Antigens, Bacterial / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D021961:Cell Membrane Structures / Q000378:metabolism*; D003840:Deoxycholic Acid / Q000737:chemistry*; D011485:Protein Binding; D012763:Shigella flexneri / Q000378:metabolism* / Q000472:pathogenicity
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C095770:IpaD protein, Shigella flexneri; D003840:Deoxycholic Acid; C087447:ipaB protein, Shigella