High Li-Ion Selectivity of Five-Coordinate Layered Titanate K2Ti2O5.

Selectivity of ion exchangers is an important topic in adsorption science owing to its specific application in resource recovery and environmental remediation. In this study, the cation exchange property of the submillimeter-sized five-coordinate K2Ti2O5 (KTO) crystals is demonstrated. Adsorption isotherm measurements were performed on KTO crystals ion-exchanged with alkali metal cations including Li+, Na+, Rb+, and Cs+. The maximum adsorption amounts of Li+, Na+, Rb+, and Cs+ on KTO were 2.70, 1.15, 0.59, and 0.42 mmol g-1, respectively, which is contradictory to the "normal" selectivity sequence (Cs+ > Rb+ > K+ > Na+ > Li+) of conventional ion exchangers, including clays and organic resins. The Kielland plots for the Li+ and Cs+ exchange experiments showed preferential Li+ adsorption on KTO, which supports the high Li+ selectivity. The interlayer distance for M+-exchanged KTO (M = Li, Na, Rb, and Cs) was dependent on cation type. Raman and X-ray absorption near-edge structure spectroscopic analyses of the KTO samples indicated that certain Ti species in KTO underwent hydrolysis, and thereby formed hydroxyl groups on the KTO surface during ion exchange. The origin of the high Li+ selectivity of KTO is discussed herein based on experimental characterization results.

Favorable Intercalation of Nitrate Ions with Fluorine-Substituted Layered Double Hydroxides.

Understanding and controlling confined nanospace to accommodate substrates and promote high ion conduction are essential to various fields. Layered double hydroxides (LDHs) have emerged as promising candidates for anion exchangers using the interlayer nanospace in their crystal structures. Miyata reported in 1983 that the affinity of anions for intercalation with most major Mg-Al LDHs increased in the following order: NO3- < Br- < F- < SO42- < HPO32-. Attempts to alter the affinity with different metal cations (M2+ and M3+) have been unsuccessful. Analyses of the crystalline structures of LDHs, positively charged host layers, interlayer anions, and interlayer water molecules indicate that they inevitably interact through hydrogen bonding. In other words, the affinity of LDHs for anions is controlled by tuning the hydrogen bonding. In this study, we prepared fluorine-substituted LDHs (F-LDHs) with different Mg/Al ratios by partially replacing the OH structural groups, which originated from the host layer, with fluorine atoms; the resulting change in affinity was investigated. The distribution coefficient, which is a useful indicator of the affinity of an LDH for a particular anion, was examined. The results showed that only F-LDHs with Mg/Al ratios of 3.5 exhibited high affinity, especially for NO3- ions, and the affinity increased in the following order: HPO42- < SO42- < F- < Br- < NO3-. The separation factors of these specific F-LDHs with respect to both NO3-/F- and NO3-/SO42- were higher than that of LDHs with other compositions by 1 order of magnitude. Raman spectroscopy above 3000 cm-1 revealed that the fluorine substitution of LDHs significantly changed the hydrogen bonding nature in the interlayer space. Highly electronegative fluorine atoms significantly decrease the extent of hydrogen bonding interactions between OH structural groups and both interlayer water molecules and anions, wherein steric effects are induced by the shrunken interlayer space, and van der Waals forces are revealed to be the predominant interaction with anions. Therefore, the highest affinity was observed for NO3- ions in F-LDHs.

Highly Crystalline Ni-Co Layered Double Hydroxide Fabricated via Topochemical Transformation with a High Adsorption Capacity for Nitrate Ions.

Layered double hydroxide (LDH) has emerged as promising candidates for removing harmful oxoanions (i.e., SO42-, HPO42-, and NO3- ions) from wastewater because of their intrinsic ability to accommodate anionic species in the interlayer space. Highly crystalline [Ni0.67Co0.33(OH)2]Cl0.29·0.53H2O (Ni-Co LDH) particles with an exceptionally high anion-exchange capacity of 58.8 mg g-1 and a distribution coefficient (Kd) of 2396 mL g-1 for NO3- ions were successfully prepared by the flux method and a topochemical strategy. Layered Na0.97Ni0.67Co0.33O2 (NNCO) was prepared using a high-temperature flux and used as a starting material for topotactic transformation consisting of oxidative hydrolysis with KOH and NaClO and subsequent reduction with H2O2 and NaCl. During the transformation from NNCO to Ni-Co LDH, a drastic change in the valences of the Ni and Co belonging to the host layer and in the cationic and anionic species occurs in interlayer space; the valences of the Ni and Co in NNCO were increased from Ni2+,3+ and Co2+,3+ to Ni3+ and Co2+,3+,4+ by an oxidative hydrolysis reaction with simultaneous intercalation of K+ ions and deintercalation of Na+ ions, and subsequently decreased from Ni3+ and Co2+,3+,4+ to Ni2+ and Co2+,3+ by a reduction reaction with simultaneous intercalation of anionic species such as CO32- and Cl- ions and deintercalation of Na+ and K+ ions. Through synchrotron powder X-ray diffraction analysis and Rietveld refinement, the resultant Ni-Co LDH was clearly shown to exhibit high crystallinity with less compositional deviation even after topochemical transformation in comparison with the one prepared by traditional coprecipitation and solid-state methods. Furthermore, the adsorption isotherm for NO3- ions elucidated that homogeneous adsorption sites are consistently constructed in the crystal structure, which could be found from the fitting to a Langmuir curve, with the R2 value being 0.98. This work opens up a new route for the fabrication of excellent not only ion-exchangeable but also ion-conductive inorganic materials for direct utilization in environmental and energy-storage processes.

Modulation effect of interlayer spacing on the superconductivity of electron-doped FeSe-based intercalates.

FeSe-based intercalates are regarded as promising candidates for high-critical temperature (Tc) superconductors. Here we present new Na- and Sr-intercalated FeSe superconductors with embedded linear diamines (H2N)CnH2n(NH2) (abbreviated as DA; n = 0, 2, 3, or 6) prepared using a low-temperature ammonothermal method to investigate the effect of interlayer spacing on the superconductivity of electron-doped FeSes. The embedded DA formed a monolayer or bilayer in the interlayer of FeSe. The interlayer spacing between nearest FeSe layers could be tuned from 0.87 to 1.14 nm without significant change in the Na/Sr content or the ratio of Fe to Se. Importantly, bilayer phases Na/ethylenediamine- and Sr/hydrazine-FeSe show improved structural stability compared to that of Na/NH3-FeSe. The series of Na- and Sr-intercalated FeSe samples exhibited nearly the same high Tc values of 41-46 and 34-38 K, respectively, irrespective of rather different interlayer spacing d. The peculiar insensitivity for both series can be ascribed to the negligible dispersions of bands along the c axis; i.e., Fermi surfaces are nearly two-dimensional when d is larger than a certain threshold value (dsat) of ∼0.9 nm. The Fermi surface shape is already optimal for Tc, and a larger d will not enhance Tc further. On the other hand, the difference in Tc between two series may be explained by the higher carrier doping level in Na/DA-FeSes compared to that in Sr/DA-FeSes, resulting in the increased density of states at the Fermi level and superconducting pairing strength.

Attitudes of acceptability and lack of condemnation toward suicide may be predictive of post-discharge suicide attempts.

BACKGROUND: Suicide attempts (SA) after psychiatric hospitalization continue to be a major cause of morbidity. Implicit measures may enhance our ability to assess suicide risk. In this context, we describe the first use of the Suicide Opinion Questionnaire (SOQ) to identify post-discharge suicide attempters. METHODS: Adult psychiatric inpatients admitted for suicidality (N = 91) were administered a battery of measures including the SOQ, and forty were reached and reassessed for SA at two months post-discharge. Exploratory factor analysis (EFA) on items associated with suicidality was performed to identify latent constructs. Linear discriminant analysis (LDA) was used to optimize factor combination for suicide identification. Results were compared with explicit measures of suicidality, and logistic regression was used to control for other risk factors. Finally, a simplified 9-item scale was derived from the results and its performance compared to that of the linear discriminant function. RESULTS: Twenty items differed between patients with and without SA at intake or follow-up. EFA on these identified two factors: suicide attempters indicated greater acceptability and less moral condemnation of suicide. The LDA-derived discriminant function and 9-item scale was significantly sensitive and specific for post-discharge SA. CONCLUSIONS: Attitudes of acceptability and lack of condemnation toward suicide may constitute an implicit measure of suicidality that could contribute to risk assessment in a high-risk population.

NH(2-) dianion entrapped in a nanoporous 12CaO·7Al2O3 crystal by ammonothermal treatment: reaction pathways, dynamics, and chemical stability.

Inorganic imides are useful for hydrogen storage and base-catalyzed reactions but are extremely unstable under ambient conditions, which hinders their practical use as functional materials. Here, we demonstrate that NH2(-) and H(-), as well as NH(2-), can be incorporated into the nanocages of the mayenite crystals, [Ca24Al28O64](4+)(e(-))4 and [Ca24Al28O64](4+)(O(2-))2, by ammonothermal treatment. We evaluated the reaction conditions and found that the anion exchange reaction proceeded at higher than 500 °C. Raman spectroscopy showed that the N-H band position of encaged NH(2-) was close to that of CaNH and MgNH crystals. We also studied the reaction pathways that yield NH2(-) and NH(2-) anions and their dynamic motions by (1)H NMR spectroscopy. Successive reactions of encaged e(-) and O(2-) ions with NH3 yielded NH2(-), NH(2-), and H(-) or OH(-), in which the O(2-) ion reacted more efficiently with NH3. The maximum NH(2-) concentration and content were ∼2.7 × 10(20) cm(-3) and ∼0.25 (wt %)NH, respectively. The short spin-lattice relaxation time found in (1)H NMR suggests that the incorporated NH2(-) and NH(2-) rotate or librate in the cage near room temperature. Stability tests showed that the encaged NH(2-) ions are chemically stable under ambient conditions and in organic solvents. These results are attributed to the encapsulation of active anions within subnanometer-sized cages composed of Ca-O-Al oxide frameworks. The encaged NH(2-) desorbed as NH3 at higher than 500 °C under vacuum (Ea = 172 kJ mol(-1)). It is thus expected that C12A7:NH(2-) will function as a reactive nitrogen source for nitrogen transfer reactions by in situ cage degradation.

Na ion-exchanged zirconium phosphate crystal with high calcium ion selectivity.

We demonstrate hydrothermally grown sodium hydrogen zirconium phosphate ((Na,H)-ZrP) crystals exhibiting high calcium ion selectivity. The standard Gibbs free energies for Ca2+ exchange on (Na,H)-ZrP and γ-type ZrP were estimated to be -10.1 and -4.69 kJ mol-1, respectively. The high Ca2+ selectivity of (Na,H)-ZrP could be attributed to the size matching between the ion exchange site of (Na,H)-ZrP and Ca2+.

Cation-Doped Nanocarbons for Enhanced Perfluoroalkyl Substance Removal: Exotic Bottom-Up Solution Plasma Synthesis and Characterization.

Perfluorinated alkyl substances (PFAS), such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), are pervasive organic contaminants that are widespread in aquatic environments, posing significant health risks to humans and wildlife. Due to their persistent nature, urgent removal is necessary. Conventional adsorbents are inefficient at removing PFOS and PFOA, highlighting the need for alternative materials. Herein, we present a synthetic method for quaternary ammonium cation-doped carbon nanoparticles (QACNs) using a solution plasma process for the efficient removal of PFOS and PFOA. QACN is formed simultaneously through a one-step discharge of nonequilibrium plasma at the interface of benzene and pyridinium chloride. The resulting material exhibited a high surface electrical charge and enhanced hydrophilicity as well as an amorphous structure of a nonporous nature, involving nanoparticles with an undefined shape. The obtained adsorbent demonstrated high adsorption efficiency and stability, adsorbing 998.45 and 889.37 mg g-1 of PFOS and PFOA, respectively, exceeding the efficiencies of conventional carbon-based adsorbents (80.89-313.15 mg g-1). The adsorption performance was dependent on the adsorbent dosage, pH of the solution, and the coexisting ionic species. Adsorption studies, including adsorption kinetics, isotherms, and thermodynamics, revealed that PFOS and PFOA were chemisorbed to the QACN surface, forming multilayers endothermically and spontaneously. Experimental and computational analyses revealed that adsorption primarily occurs via electronic interactions between the PFAS active sites and the quaternary ammonium group in the carbon framework. The slightly lower adsorption potential of the PFOS and PFOA fluorocarbon chains on the adsorbent was elucidated. Furthermore, the dispersibility of the adsorbent in solution significantly affected the adsorption performance. These findings highlight the potential of the novel synthetic method proposed in this study, offering a pathway for the development of highly effective carbon adsorbents for environmental remediation.

CCR4-dependent regulatory T cell function in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is an idiopathic inflammatory disease of the intestine. CD4(+) T lymphocytes play an important role in both initiating and regulating intestinal inflammatory immune responses. CD4(+)CD25(+)CD45RB(low) regulatory T (T reg) cells are capable of preventing the development of colitis in a mouse model of IBD. The precise mechanism of T reg cell-mediated prevention of colitis in this model is unclear, and the role of chemokine receptors in the trafficking and function of T reg cells in this model has not been determined. We examined the role of the chemokine receptor CCR4 in in vivo trafficking and suppressive function of T reg cells in a mouse adoptive transfer model of IBD. CCR4-deficient T reg cells failed to accumulate in the mesenteric lymph nodes (MLNs) at early time points (2-5 d) after adoptive transfer, resulting in a failure to suppress the generation of pathogenic T cells and the development of colitis. Moreover, although CCR4-deficent T cells had equivalent in vitro suppressive activity and accumulated in MLNs at later time points (42-56 d), they were unable to suppress colitis. Our study demonstrates that CCR4 plays an important role in T reg cell trafficking in LNs and that this is critical for T reg cell suppressive function in vivo.

Layer-Stacking Sequence Governs Ion-Storage in Layered Double Hydroxides.

In layered materials, the layer-stacking sequence allows the tuning of ion transport and storage properties by modulating the host-ion interactions. However, unlike in the case of cations, the relationship between the stacking sequence and anion transport and storage properties is less clearly understood. Herein, we demonstrate that the stacking sequence governs the nitrate-storage properties of layered double hydroxides (LDHs); the 2H1 polytype enhances the nitrate-storage capacity to 400% of that of the 3R1 polytype. A quartz crystal microbalance with dissipation monitoring combined with multimodal ex situ experiments indicated that the high ion-storage capacity of the 2H1 polytype originates from the soft nature of LDHs lattices, which facilitates nitrate with minimal lattice changes. In contrast, the rigid lattice of the 3R1 sequence requires a notably large lattice expansion, which is detrimental to ion storage. Our findings can aid the rational design of anion-host interaction-derived functionalities.

Critical role of water structure around interlayer ions for ion storage in layered double hydroxides.

Water-containing layered materials have found various applications such as water purification and energy storage. The highly structured water molecules around ions under the confinement between the layers determine the ion storage ability. Yet, the relationship between the configuration of interlayer ions and water structure in high ion storage layered materials is elusive. Herein, using layered double hydroxides, we demonstrate that the water structure is sensitive to the filling density of ions in the interlayer space and governs the ion storage. For ion storage of dilute nitrate ions, a 24% decrease in the filling density increases the nitrate storage capacity by 300%. Quartz crystal microbalance with dissipation monitoring studies, combined with multimodal ex situ experiments and theoretical calculations, reveal that the decreasing filling density effectively facilitates the 2D hydrogen-bond networking structure in water around interlayer nitrate ions along with minimal change in the layered structure, leading to the high storage capacity.

Flux Growth of Single-Crystalline Hollandite-Type Potassium Ferrotitanate Microrods From KCl Flux.

Hollandite-type crystals have unique and interesting physical and chemical properties. Here, we report the flux growth of hollandite-type single-crystalline potassium ferrotitanate (KFTO) with faceted surface features from a KCl flux. We varied the flux growth conditions, including the kind of flux, holding temperature, and solute concentration for growing faceted crystallites. KCl was found to be the best flux to grow the single-crystalline KFTO particles, while heating at or above 900°C was needed to yield the KFTO single crystals. The crystal growth was only weakly dependent on the solute concentration. Next, we characterized the grown single crystals and discussed the manner of their growth from the KCl flux. TEM images with clear electron diffraction spots indicated that the KFTO crystals grew along the <001> direction to form microrods ~10 µm in size. DFT calculation results indicated that the surface energy of the (100) face is lower than that of the (001) face. Based on these characterization results, we proposed a possible growth mechanism of the KFTO crystals.

Human lupus autoantibody-DNA complexes activate DCs through cooperation of CD32 and TLR9.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by pathogenic autoantibodies against nucleoproteins and DNA. Here we show that DNA-containing immune complexes (ICs) within lupus serum (SLE-ICs), but not protein-containing ICs from other autoimmune rheumatic diseases, stimulates plasmacytoid DCs (PDCs) to produce cytokines and chemokines via a cooperative interaction between Toll-like receptor 9 (TLR9) and FcgammaRIIa (CD32). SLE-ICs transiently colocalized to a subcellular compartment containing CD32 and TLR9, and CD32+, but not CD32-, PDCs internalized and responded to SLE-ICs. Our findings demonstrate a novel functional interaction between Fc receptors and TLRs, defining a pathway in which CD32 delivers SLE-ICs to intracellular lysosomes containing TLR9, inducing a signaling cascade leading to PDC activation. These data demonstrate that endogenous DNA-containing autoantibody complexes found in the serum of patients with SLE activate the innate immune system and suggest a novel mechanism whereby these ICs contribute to the pathogenesis of this autoimmune disease.

Superconductivity and phase instability of NH3-free Na-intercalated FeSe(1-z)S(z).

The discovery of ThCr2Si2-type A(x)Fe(2-y)Se2 (A = K, Rb, Cs and Tl) with Tc ~30 K make much progress in iron-based superconducting field, but their multiple-phase separations are disadvantageous for understanding the origin. On the other hand, for small alkali metals, studies on (Li,Na)FeCu(S,Se)2 and NaFe(2-δ)S2 show that these compounds possess CaAl2Si2-type structure, implying that ThCr2Si2-type structure is unstable for small alkali metal-intercalated FeSe under high temperature. Here we report a new intercalate Na0.65(1)Fe1.93(1)Se2 with Tc ~37 K, synthesized by low-temperature ammonothermal method. The notable finding is that the Na0.65(1)Fe1.93(1)Se2 shows a ThCr2Si2-type structure, which is the first instance of small-sized alkali metal intercalates without NH3 co-intercalation. Besides, the NH3-poor Na0.80(4)(NH3)0.60Fe1.86(1)Se2 and NH3-rich phase with Tcs at 45 and 42 K are identified by tuning the concentration of Na-NH3 solutions. The modulation of interlayer spacing reveals the versatile evolution of structural stability and superconductivity in these intercalates.

Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store.

Industrially, the artificial fixation of atmospheric nitrogen to ammonia is carried out using the Haber-Bosch process, but this process requires high temperatures and pressures, and consumes more than 1% of the world's power production. Therefore the search is on for a more environmentally benign process that occurs under milder conditions. Here, we report that a Ru-loaded electride [Ca(24)Al(28)O(64)](4+)(e(-))(4) (Ru/C12A7:e(-)), which has high electron-donating power and chemical stability, works as an efficient catalyst for ammonia synthesis. Highly efficient ammonia synthesis is achieved with a catalytic activity that is an order of magnitude greater than those of other previously reported Ru-loaded catalysts and with almost half the reaction activation energy. Kinetic analysis with infrared spectroscopy reveals that C12A7:e(-) markedly enhances N(2) dissociation on Ru by the back donation of electrons and that the poisoning of ruthenium surfaces by hydrogen adatoms can be suppressed effectively because of the ability of C12A7:e(-) to store hydrogen reversibly.

Toll-like receptors stimulate human neutrophil function.

The first immune cell to arrive at the site of infection is the neutrophil. Upon arrival, neutrophils quickly initiate microbicidal functions, including the production of antimicrobial products and proinflammatory cytokines that serve to contain infection. This allows the acquired immune system enough time to generate sterilizing immunity and memory. Neutrophils detect the presence of a pathogen through germ line-encoded receptors that recognize microbe-associated molecular patterns. In vertebrates, the best characterized of these receptors are Toll-like receptors (TLRs). We have determined the expression and function of TLRs in freshly isolated human neutrophils. Neutrophils expressed TLR1, 2, 4, 5, 6, 7, 8, 9, and 10-all the TLRs except TLR3. Granulocyte-macrophage colony-stimulating factor (GM-CSF) treatment increased TLR2 and TLR9 expression levels. The agonists of all TLRs expressed in neutrophils triggered or primed cytokine release, superoxide generation, and L-selectin shedding, while inhibiting chemotaxis to interleukin-8 (IL-8) and increasing phagocytosis of opsonized latex beads. The response to the TLR9 agonist nonmethylated CpG-motif-containing DNA (CpG DNA) required GM-CSF pretreatment, which also enhanced the response to the other TLR agonists. Finally, using quantitative polymerase chain reaction (QPCR), we demonstrate a chemokine expression profile that suggests that TLR-stimulated neutrophils recruit innate, but not acquired, immune cells to sites of infection.

The Toll-like receptor 5 stimulus bacterial flagellin induces maturation and chemokine production in human dendritic cells.

Toll-like receptors (TLRs) are pattern recognition receptors that serve an important function in detecting pathogens and initiating inflammatory responses. Upon encounter with foreign Ag, dendritic cells (DCs) go through a maturation process characterized by an increase in surface expression of MHC class II and costimulatory molecules, which leads to initiation of an effective immune response in naive T cells. The innate immune response to bacterial flagellin is mediated by TLR5, which is expressed on human DCs. Therefore, we sought to investigate whether flagellin could induce DC maturation. Immature DCs were cultured in the absence or presence of flagellin and monitored for expression of cell surface maturation markers. Stimulation with flagellin induced increased surface expression of CD83, CD80, CD86, MHC class II, and the lymph node-homing chemokine receptor CCR7. Flagellin stimulated the expression of chemokines active on neutrophils (IL-8/CXC chemokine ligand (CXCL)8, GRO-alpha/CXCL1, GRO-beta/CXCL2, GRO-gamma/CXCL3), monocytes (monocyte chemoattractant protein-1/CC chemokine ligand (CCL)2), and immature DCs (macrophage-inflammatory protein-1 alpha/CCL3, macrophage-inflammatory protein-1 beta/CCL4), but not chemokines active on effector T cells (IFN-inducible protein-10 kDa/CXCL10, monokine induced by IFN-gamma/CXCL9, IFN-inducible T cell alpha chemoattractant/CXCL11). However, stimulating DCs with both flagellin and IFN-inducible protein-10 kDa, monokine induced by IFN-gamma, and IFN-inducible T cell alpha chemoattractant expression, whereas stimulation with IFN-beta or flagellin alone failed to induce these chemokines. In functional assays, flagellin-matured DCs displayed enhanced T cell stimulatory activity with a concomitant decrease in endocytic activity. Finally, DCs isolated from mouse spleens or bone marrows were shown to not express TLR5 and were not responsive to flagellin stimulation. These results demonstrate that flagellin can directly stimulate human but not murine DC maturation, providing an additional mechanism by which motile bacteria can initiate an acquired immune response.

Serpin 2a is induced in activated macrophages and conjugates to a ubiquitin homolog.

After i.p. infection of mice with the intracellular bacterium Mycobacterium bovis bacillus Calmette-Guérin, macrophages recovered from the peritoneal cavity display classical signs of immune activation. We have identified a member of the serine protease inhibitor (serpin) family which is highly induced in macrophages during bacillus Calmette-Guérin infection. Serpin 2a (spi2a) expression is also induced in macrophages in vivo during infection with Salmonella typhimurium and Listeria monocytogenes, and in vitro by a variety of bacteria and bacterial products. The cytokine IFN-gamma also induces spi2a expression in macrophages, and this induction is synergistic with bacterial products. We also demonstrate here that a ubiquitin homolog, IFN-stimulated gene of 15-kDa (ISG15), is strongly induced during in vitro and in vivo activation of macrophages and that it conjugates to spi2a in activated macrophages. The ISG15-spi2a conjugates were identified by tandem mass spectrometry and contained spi2a conjugated to either one or two molecules of ISG15. Whereas spi2a was induced by either bacterial products or IFN-gamma, ISG15 was induced only by bacterial products. Although many protein targets have been described for ubiquitin conjugation, spi2a is the first ISG15-modified protein to be reported. Macrophage activation is accompanied by the activation of a variety of proteases. It is of interest that a member of the serine protease inhibitor family is concomitantly induced and modified by a ubiquitin-like protein.

Toll-like receptor 5 recognizes a conserved site on flagellin required for protofilament formation and bacterial motility.

Toll-like receptor 5 (TLR5) recognizes bacterial flagellin and activates host inflammatory responses. In this study, we examine the nature of the TLR5-flagellin interaction. With deletional, insertional and alanine-scanning mutagenesis, we precisely mapped the TLR5 recognition site on flagellin to a cluster of 13 amino acid residues that participate in intermolecular interactions within flagellar protofilaments and that are required for bacterial motility. The recognition site is buried in the flagellar filament, and monomeric flagellin, but not the filamentous molecule, stimulated TLR5. Finally, flagellin coprecipitated with TLR5, indicating close physical interaction between the molecules. These studies demonstrate the exquisite ability of the innate immune system to precisely target a conserved site on flagellin that is essential for bacterial motility.