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"Berry, Richard"
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Catch bond drives stator mechanosensitivity in the bacterial flagellar motor
The bacterial flagellar motor (BFM) is the rotary motor that rotates each bacterial flagellum, powering the swimming and swarming of many motile bacteria. The torque is provided by stator units, ion motive force-powered ion channels known to assemble and disassemble dynamically in the BFM. This turnover is mechanosensitive, with the number of engaged units dependent on the viscous load experienced by the motor through the flagellum. However, the molecular mechanism driving BFM mechanosensitivity is unknown. Here, we directly measure the kinetics of arrival and departure of the stator units in individual motors via analysis of high-resolution recordings of motor speed, while dynamically varying the load on the motor via external magnetic torque. The kinetic rates obtained, robust with respect to the details of the applied adsorption model, indicate that the lifetime of an assembled stator unit increases when a higher force is applied to its anchoring point in the cell wall. This provides strong evidence that a catch bond (a bond strengthened instead of weakened by force) drives mechanosensitivity of the flagellar motor complex. These results add the BFM to a short, but growing, list of systems demonstrating catch bonds, suggesting that this “molecular strategy” is a widespread mechanism to sense and respond to mechanical stress. We propose that force-enhanced stator adhesion allows the cell to adapt to a heterogeneous environmental viscosity and may ultimately play a role in surface-sensing during swarming and biofilm formation.
Journal Article
22 Bullets
For the past three years Charly Mattei has led a peaceful life, devoting himself to his wife and children. Then one winter morning, he's left for dead in the parking garage in Marseille's Old Port, with 22 bullets in his body. Against all the odds, he doesnt die. Now this former member of the Marseille mafia is hell bent on revenge, and will stop at nothing to destroy all those involved in his attempted assassination. Many more than those destructive 22 Bullets will fly before Charly (The Immortal) finally settles the score.
DVD
Composition, Formation, and Regulation of the Cytosolic C-ring, a Dynamic Component of the Type III Secretion Injectisome
Many gram-negative pathogens employ a type III secretion injectisome to translocate effector proteins into eukaryotic host cells. While the structure of the distal \"needle complex\" is well documented, the composition and role of the functionally important cytosolic complex remain less well understood. Using functional fluorescent fusions, we found that the C-ring, an essential and conserved cytosolic component of the system, is composed of ~22 copies of SctQ (YscQ in Yersinia enterocolitica), which require the presence of YscQC, the product of an internal translation initiation site in yscQ, for their cooperative assembly. Photoactivated localization microscopy (PALM) reveals that in vivo, YscQ is present in both a free-moving cytosolic and a stable injectisome-bound state. Notably, fluorescence recovery after photobleaching (FRAP) shows that YscQ exchanges between the injectisome and the cytosol, with a t½ of 68 ± 8 seconds when injectisomes are secreting. In contrast, the secretin SctC (YscC) and the major export apparatus component SctV (YscV) display minimal exchange. Under non-secreting conditions, the exchange rate of YscQ is reduced to t½ = 134 ± 16 seconds, revealing a correlation between C-ring exchange and injectisome activity, which indicates a possible role for C-ring stability in regulation of type III secretion. The stabilization of the C-ring depends on the presence of the functional ATPase SctN (YscN). These data provide new insights into the formation and composition of the injectisome and present a novel aspect of type III secretion, the exchange of C-ring subunits, which is regulated with respect to secretion.
Journal Article
Cellulose nanocrystal–alginate hydrogel beads as novel adsorbents for organic dyes in aqueous solutions
A new generation of recyclable adsorbents comprising of cellulose nanocrystals and alginate (CNC–ALG) with superior adsorption capacity was developed. Sustainable nanomaterials like cellulose nanocrystals derived from pulp fibres and cellulosic biomass are ideal systems to remove contaminants in our water systems. Their use will reduce our dependence on adsorbents, such as activated carbon that contribute to greenhouse gases production. Adsorption characteristics of CNC–ALG hydrogel beads were evaluated using batch adsorption studies of methylene blue (MB) in aqueous solution. The influence of various parameters, such as contact time, adsorbent dosage, initial dye concentration, pH, temperature, ionic strength, crosslinking time and bead size on the MB adsorption were investigated. Thermodynamic analyses confirmed that the adsorption process is spontaneous and exothermic. The kinetics and mechanism of adsorption were best described by a pseudo-second order kinetic model and intra-particle diffusion model. Equilibrium adsorption data fitted well to the Langmuir adsorption isotherm yielding a maximum adsorption capacity of 256.41 mg/g, which is comparable to activated carbon. We demonstrated that after five adsorption–desorption cycles, the removal efficiency of MB remained at ~97 %, and the CNC–ALG hydrogel beads are effective adsorbents for the removal of organic dyes from wastewaters.
Journal Article
Cryo-EM structures provide insight into how E. coli F1Fo ATP synthase accommodates symmetry mismatch
F
1
F
o
ATP synthase functions as a biological rotary generator that makes a major contribution to cellular energy production. It comprises two molecular motors coupled together by a central and a peripheral stalk. Proton flow through the F
o
motor generates rotation of the central stalk, inducing conformational changes in the F
1
motor that catalyzes ATP production. Here we present nine cryo-EM structures of
E. coli
ATP synthase to 3.1–3.4 Å resolution, in four discrete rotational sub-states, which provide a comprehensive structural model for this widely studied bacterial molecular machine. We observe torsional flexing of the entire complex and a rotational sub-step of F
o
associated with long-range conformational changes that indicates how this flexibility accommodates the mismatch between the 3- and 10-fold symmetries of the F
1
and F
o
motors. We also identify density likely corresponding to lipid molecules that may contribute to the rotor/stator interaction within the F
o
motor.
F
1
F
o
ATP synthase consists of two coupled rotary molecular motors: the soluble ATPase F
1
and the transmembrane F
o
. Here, the authors present cryo-EM structures of
E. coli
ATP synthase in four discrete rotational sub-states at 3.1-3.4 Å resolution and observe a rotary sub-step of the F
o
motor cring that reveals the mechanism of elastic coupling between the two rotary motors, which is essential for effective ATP synthesis.
Journal Article
Bacterial flagellar motor
The bacterial flagellar motor is a reversible rotary nano-machine, about 45 nm in diameter, embedded in the bacterial cell envelope. It is powered by the flux of H+ or Na+ ions across the cytoplasmic membrane driven by an electrochemical gradient, the proton-motive force or the sodium-motive force. Each motor rotates a helical filament at several hundreds of revolutions per second (hertz). In many species, the motor switches direction stochastically, with the switching rates controlled by a network of sensory and signalling proteins. The bacterial flagellar motor was confirmed as a rotary motor in the early 1970s, the first direct observation of the function of a single molecular motor. However, because of the large size and complexity of the motor, much remains to be discovered, in particular, the structural details of the torque-generating mechanism. This review outlines what has been learned about the structure and function of the motor using a combination of genetics, single-molecule and biophysical techniques, with a focus on recent results and single-molecule techniques.
Journal Article
Surface modification of cellulose nanocrystal with chitosan oligosaccharide for drug delivery applications
A novel drug delivery system based on two of the most abundant natural biopolymers was developed by modifying the surface of oxidized cellulose nanocrystal (CNC) with chitosan oligosaccharide (CS
OS
). First, the primary alcohol moieties of CNC were selectively oxidized to carboxyl groups using the 2,2,6,6-tetramethylpiperidine-1-oxyl radical catalyst. The amino groups of CS
OS
were then reacted with carboxylic acid groups on oxidized CNC (CNC-OX) via the carbodiimide reaction using
N
-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide as coupling agents. Successful grafting of CS
OS
to CNC-OX was confirmed by infrared spectroscopy, thermogravimetry, potentiometric titration, and zeta potential measurements. The grafting resulted in a conversion of ~90 % carboxyl groups on CNC-OX and the degree of substitution was 0.26. CNC–CS
OS
nanoparticles showed a binding efficiency of 21.5 % and a drug loading of 14 % w/w. A drug selective electrode was used to directly measure the concentration of procaine hydrochloride released from CNC–CS
OS
particles. The in vitro drug release was studied at pH 8 and the nanoparticles revealed a fast release of up to 1 h, which can be used as biocompatible and biodegradable drug carriers for transdermal delivery applications.
Journal Article
Cellulose nanocrystals as promising adsorbents for the removal of cationic dyes
Cellulose nanocrystals (CNCs) prepared from cellulose fibre via sulfuric acid hydrolysis was used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of pH, adsorbent dosage, temperature, ionic strength, initial dye concentration were studied to optimize the conditions for the maximum adsorption of dye. Adsorption equilibrium data was fitted to both Langmuir and Freundlich isotherm models, where the Langmuir model better described the adsorption process. The maximum adsorption capacity was 118 mg dye/g CNC at 25 °C and pH 9. Calculated thermodynamic parameters, such as free energy change (ΔG = −20.8 kJ/mol), enthalpy change (ΔH = −3.45 kJ/mol), and entropy change (ΔS = 0.58 kJ/mol K) indicates that MB adsorption on CNCs is a spontaneous exothermic process. Tunability of the adsorption capacity by surface modification of CNCs was shown by oxidizing the primary hydroxyl groups on the CNC surface with TEMPO reagent and the adsorption capacity was increased from 118 to 769 mg dye/g CNC.
Journal Article
Modulation of innate and adaptive immunity by cytomegaloviruses
The coordinated activities of innate and adaptive immunity are critical for effective protection against viruses. To counter this, some viruses have evolved sophisticated strategies to circumvent immune cell recognition. In particular, cytomegaloviruses encode large arsenals of molecules that seek to subvert T cell and natural killer cell function via a remarkable array of mechanisms. Consequently, these ‘immunoevasins’ play a fundamental role in shaping the nature of the immune system by driving the evolution of new immune receptors and recognition mechanisms. Here, we review the diverse strategies adopted by cytomegaloviruses to target immune pathways and outline the host’s response.This Review focuses on the cytomegaloviruses and the sophisticated strategies they have evolved to evade immune recognition. The authors suggest a better appreciation of these pathways could have clinical implications beyond antiviral immunity, for instance in understanding immune evasion in cancer.
Journal Article