title: Oligomerization and activation of the FliI ATPase central to bacterial flagellum assembly.
abstract: FliI is the peripheral membrane ATPase pivotal to the type III protein export mechanism underlying the assembly of the bacterial flagellum. Gel filtration and multiangle light scattering showed that purified soluble native FliI protein was in a monomeric state but, in the presence of ATP, FliI showed a propensity to oligomerize. Electron microscopy revealed that FliI assembles to a ring structure, the yield of which was increased by the presence of a non-hydrolysable ATP analogue. Single particle analysis of the resulting electron micrograph images, to which no symmetry was applied, showed that the FliI ring structure has sixfold symmetry and an external diameter of approximately 10 nm. The oligomeric ring has a central cavity of 2.5-3.0 nm, which is comparable to the known diameter of the flagellar export channel into which export substrates feed. Enzymatic activity of the FliI ATPase showed positive co-operativity, establishing that oligomerization and enzyme activity are coupled. Escherichia coli phospholipids increased enzyme co-operativity, and in vitro cross-linking demonstrated that they promoted FliI multimerization. The data reveal central facets of the structure and action of the flagellar assembly ATPase and, by extension, the homologous ATPases of virulence-related type III export systems.
authors.affiliation: Cambridge University, Department of Pathology, Tennis Court Road, UK.
authors.forename: Laurent
authors.initials: L
authors.lastname: Claret
authors.forename: Susannah R
authors.initials: SR
authors.lastname: Calder
authors.forename: Matthew
authors.initials: M
authors.lastname: Higgins
authors.forename: Colin
authors.initials: C
authors.lastname: Hughes
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D019281:Dimerization; D004789:Enzyme Activation; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005407:Flagella / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D010743:Phospholipids / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C489554:FliL protein, E coli; D008565:Membrane Proteins; D010743:Phospholipids; C074426:FliL protein, Bacteria; D000251:Adenosine Triphosphatases