Katsumi Imada

Construction of the bacterial flagellum in the cell exterior proceeds at its distal end by highly ordered self-assembly of many different component proteins, which are selectively exported through the central channel of the growing flagellum by the flagellar type III export apparatus. FliI is the ATPase of the export apparatus that drives the export process. Here we report the 2.4 A resolution crystal structure of FliI in the ADP-bound form. FliI consists of three domains, and the whole structur

The bacterial flagellar motor can rotate either clockwise (CW) or counterclockwise (CCW). Three flagellar proteins, FliG, FliM, and FliN, are required for rapid switching between the CW and CCW directions. Switching is achieved by a conformational change in FliG induced by the binding of a chemotaxis signaling protein, phospho-CheY, to FliM and FliN. FliG consists of three domains, FliG(N), FliG(M), and FliG(C), and forms a ring on the cytoplasmic face of the MS ring of the flagellar basal body.

FlhA is the largest integral membrane component of the flagellar type III protein export apparatus of Salmonella and is composed of an N-terminal transmembrane domain (FlhA(TM)) and a C-terminal cytoplasmic domain (FlhA(C)). FlhA(C) is thought to form a platform of the export gate for the soluble components to bind to for efficient delivery of export substrates to the gate. Here, we report a structure of FlhA(C) at 2.8 A resolution. FlhA(C) consists of four subdomains (A(C)D1, A(C)D2, A(C)D3 and

For self-assembly of the bacterial flagellum, most of the flagellar component proteins synthesized in the cytoplasm are exported by the flagellar type III export apparatus to the growing, distal end. Flagellar protein export is highly organized and well controlled in every step of the flagellar assembly process. Flagellar-specific chaperones not only facilitate the export of their cognate proteins, as well as prevent their premature aggregation in the cytoplasm, but also play a role in fine-tuni

The bacterial flagellar type III export apparatus, which is required for flagellar assembly beyond the cell membranes, consists of a transmembrane export gate complex and a cytoplasmic ATPase complex. FlhA, FlhB, FliP, FliQ, and FliR form the gate complex inside the basal body MS ring, although FliO is required for efficient export gate formation in Salmonella enterica. However, it remains unknown how they form the gate complex. Here we report that FliP forms a homohexameric ring with a diameter

Escherichia coli has closely related amino acid chemoreceptors with distinct ligand specificity, Tar for l-aspartate and Tsr for l-serine. Crystallography of the ligand-binding domain of Tar identified the residues interacting with aspartate, most of which are conserved in Tsr. However, swapping of the nonconserved residues between Tsr and Tar did not change ligand specificity. Analyses with chimeric receptors led us to hypothesize that distinct three-dimensional arrangements of the conserved li

FliI and FliJ form the FliI6FliJ ATPase complex of the bacterial flagellar export apparatus, a member of the type III secretion system. The FliI6FliJ complex is structurally similar to the α3β3γ complex of F1-ATPase. The FliH homodimer binds to FliI to connect the ATPase complex to the flagellar base, but the details are unknown. Here we report the structure of the homodimer of a C-terminal fragment of FliH (FliHC2) in complex with FliI. FliHC2 shows an unusually asymmetric homodimeric structure

The Dot/Icm type IVB secretion system (T4BSS) is a pivotal determinant of Legionella pneumophila pathogenesis. L. pneumophila translocate more than 100 effector proteins into host cytoplasm using Dot/Icm T4BSS, modulating host cellular functions to establish a replicative niche within host cells. The T4BSS core complex spanning the inner and outer membranes is thought to be made up of at least five proteins: DotC, DotD, DotF, DotG and DotH. DotH is the outer membrane protein; its targeting depen