title: Interaction with type IV pili induces structural changes in the bacterial outer membrane secretin PilQ.
abstract: Type IV pili are cell surface organelles found on many Gram-negative bacteria. They mediate a variety of functions, including adhesion, twitching motility, and competence for DNA uptake. The type IV pilus is a helical polymer of pilin protein subunits and is capable of rapid polymerization or depolymerization, generating large motor forces in the process. Here we show that a specific interaction between the outer membrane secretin PilQ and the type IV pilus fiber can be detected by far-Western analysis and sucrose density gradient centrifugation. Transmission electron microscopy of preparations of purified pili, to which the purified PilQ oligomer had been added, showed that PilQ was uniquely located at one end of the pilus fiber, effectively forming a "mallet-type" structure. Determination of the three-dimensional structure of the PilQ-type IV pilus complex at 26-angstroms resolution showed that the cavity within the protein complex was filled. Comparison with a previously determined structure of PilQ at 12-angstroms resolution indicated that binding of the pilus fiber induced a dissociation of the "cap" feature and lateral movement of the "arms" of the PilQ oligomer. The results demonstrate that the PilQ structure exhibits a dynamic response to the binding of its transported substrate and suggest that the secretin could play an active role in type IV pilus assembly as well as secretion.
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Faculty of Life Sciences, Sackville Street, P. O. Box 88, Manchester M60 1QD, United Kingdom.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.forename: Stephan A
authors.initials: SA
authors.lastname: Frye
authors.forename: Seetha
authors.initials: S
authors.lastname: Balasingham
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ford
authors.forename: Tone
authors.initials: T
authors.lastname: Tønjum
authors.forename: Jeremy P
authors.initials: JP
authors.lastname: Derrick
mesh_terms: D015153:Blotting, Western; D002499:Centrifugation, Density Gradient; D004247:DNA / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D036781:Fimbriae Proteins / Q000737:chemistry* / Q000378:metabolism; D010861:Fimbriae, Bacterial / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D046529:Microscopy, Electron, Transmission; D009345:Neisseria meningitidis / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D013395:Sucrose / Q000494:pharmacology
chemical_list: D011994:Recombinant Proteins; C084295:pilQ protein, bacteria; D036781:Fimbriae Proteins; D006639:Histidine; D013395:Sucrose; D004247:DNA