Regulation of phosphate starvation-specific responses in Escherichia coli.

Toxic agents added into the medium of rapidly growing Escherichia coli induce specific stress responses through the activation of specialized transcription factors. Each transcription factor and downstream regulon (e.g. SoxR) are linked to a unique stress (e.g. superoxide stress). Cells starved of phosphate induce several specific stress regulons during the transition to stationary phase when the growth rate is steadily declining. Whereas the regulatory cascades leading to the expression of specific stress regulons are well known in rapidly growing cells stressed by toxic products, they are poorly understood in cells starved of phosphate. The intent of this review is to both describe the unique mechanisms of activation of specialized transcription factors and discuss signalling cascades leading to the induction of specific stress regulons in phosphate-starved cells. Finally, I discuss unique defence mechanisms that could be induced in cells starved of ammonium and glucose.

Density Functional Theory Study of the Point Defects on KDP (100) and (101) Surfaces.

Surface defects are usually associated with the formation of other forms of expansion defects in crystals, which have an impact on the crystals' growth quality and optical properties. Thereby, the structure, stability, and electronic structure of the hydrogen and oxygen vacancy defects (VH and VO) on the (100) and (101) growth surfaces of KDP crystals were studied by using density functional theory. The effects of acidic and alkaline environments on the structure and properties of surface defects were also discussed. It has been found that the considered vacancy defects have different properties on the (100) and (101) surfaces, especially those that have been reported in the bulk KDP crystals. The (100) surface has a strong tolerance for surface VH and VO defects, while the VO defect causes a large lattice relaxation on the (101) surface and introduces a deep defect level in the band gap, which damages the optical properties of KDP crystals. In addition, the results show that the acidic environment is conducive to the repair of the VH defects on the surface and can eliminate the defect states introduced by the surface VO defects, which is conducive to improving the quality of the crystal surface and reducing the defect density. Our study opens up a new way to understand the structure and properties of surface defects in KDP crystals, which are different from the bulk phase, and also provides a theoretical basis for experimentally regulating the surface defects in KDP crystals through an acidic environment.

Synthesis and biological evaluation of modified laminin peptide (N2S2-KDP) with enhanced affinity for neuronal growth and targeted molecular imaging (SPECT).

An analog of γ1 laminin (RDIAEIIKDI) decapeptide has been used to augment neuronal survival and regeneration after injuries, during aging and other CNS disorder. As a prime synthetic peptide, KDI, is responsible for the neurite outgrowth of human embryonic neurons. In this study, we have designed, modified a KDI derivative and synthesized by replacing isoleucine (I) with Pro (P) amino acid at C-terminal to enhance its potency towards neurite growth. -Cys-Gly-Cys (-CGC) N2S2 motif was also incorporated in the present design for peptide radiolabeling. The modified peptide showed a better binding with the desired 3T1M receptor for neurite growth. The peptide was synthesized using solid phase peptide synthesis and Fmoc-strategy with more than 80% yield. The receptor binding studies of 99mTc-N2S2-KDP in Neuro2A cell lines showed Kd value in 31 nM range and the complex showed appreciable brain uptake in mice. The results on human SH-SY5Y indicate that the unlabeled N2S2-KDP may perhaps be useful for neurite growth in neurodegenerative disorder.

A Review of Small Molecule Inhibitors and Functional Probes of Human Cathepsin L.

Human cathepsin L belongs to the cathepsin family of proteolytic enzymes with primarily an endopeptidase activity. Although its primary functions were originally thought to be only of a housekeeping enzyme that degraded intracellular and endocytosed proteins in lysosome, numerous recent studies suggest that it plays many critical and specific roles in diverse cellular settings. Not surprisingly, the dysregulated function of cathepsin L has manifested itself in several human diseases, making it an attractive target for drug development. Unfortunately, several redundant and isoform-specific functions have recently emerged, adding complexities to the drug discovery process. To address this, a series of chemical biology tools have been developed that helped define cathepsin L biology with exquisite precision in specific cellular contexts. This review elaborates on the recently developed small molecule inhibitors and probes of human cathepsin L, outlining their mechanisms of action, and describing their potential utilities in dissecting unknown function.

Absolute quantification of the Kdp subunits of Escherichia coli by multiple reaction monitoring.

The sensor kinase/response regulator system KdpD/KdpE of Escherichia coli regulates the expression of the kdpFABC operon, encoding the high-affinity KdpFABC potassium (K(+) )-transport complex. Additionally, it has been suggested that the kdpDE operon itself is subjected to autoregulation by its gene products KdpD and KdpE. However, since kdpFABC and kdpDE expression has mainly been studied on the transcriptional level, accurate information on absolute amounts and the stoichiometric subunit composition of KdpFABC and KdpD/KdpE under K(+) -limiting and K(+) -nonlimiting growth conditions are lacking. In this study, we used highly sensitive mass spectrometric methods to quantify the amount of subunits of the Kdp(F)ABC complex and KdpD/KdpE. Data-dependent shotgun MS was used to assess protein coverage and accessible peptides. Absolute amounts of Kdp(F)ABC and KdpD/KdpE were quantified by targeted MRM analysis in the presence of corresponding heavy labeled standard peptides. Baseline synthesis of Kdp(F)ABC and KdpD/KdpE was found to be in the attomolar range under K(+) -nonlimiting conditions. Under K(+) -limitation, synthesis of Kdp(F)ABC (KdpA:KdpB:KdpC ratio of 1:1:1) was amplified more than 100-fold, whereas only a tenfold amplification of KdpD/KdpE (KdpD:KdpE ratio of 1:4) was observed. The results obtained provide a solid basis for follow-up studies on the dynamic regulation of the Kdp system.

A novel water-in-deep eutectic solvent microemulsions for chemical polishing of single crystal KDP.

Microemulsion (ME) has been investigated as a chemical polishing (CP) fluid for effective polishing of single crystal potassium dihydrogen phosphate (KDP), perfectly avoiding the generation of mechanical stress. In this work, a water-in-deep eutectic solvent ME was proposed as the polishing fluid for CP of single crystal KDP. Deep eutectic solvent (DES) is formulated using n-octanol as hydrogen bond donor and methyltrioctylammonium chloride (MTOAC) as hydrogen bond acceptor, with a mass ratio of 2:1. The ME was prepared by mixing DES as the oil phase (12.5 %, wt.), a hydrochloric acid solution as the water phase (12.5 %, wt.), and isopropanol as the cosolvent (75 %, wt.), without adding any other surfactants. The properties of the ME were characterized by conductivity measurements and ultraviolet (UV) spectroscopy. The reactivity of ME with KDP was measured by the conductivity method, and it was higher at low pH values. A hydrochloric acid solution with a pH of 3 was selected as aqueous phase, considering its effects on particle size, salt loading, and static etching rate. The water content affects the polarity of ME and the final water content was determined to be 12.5 % to ensure high polarity of ME. The surface quality of the KDP crystals before and after polishing was examined using grazing incidence X-ray diffraction (GIXRD) analysis. The average roughness of the KDP crystal surface was decreased from 1.96 nm to 1.43 nm, and the root-mean-square (RMS) roughness was reduced from 2.81 nm to 1.86 nm, demonstrating a significant polishing effect. Finally, the polishing mechanism was elucidated in terms of the irreversible chemical reaction between the active components in the microemulsion and the KDP crystals.

Computational study of K vacancy with an H interstitial defect in KH2PO4 crystal.

The electronic structures, defect formations, defect transition levels and optical properties for VK+Hi defect models in KDP crystals have been studied based on DFT. Lattice dynamics methods give the most reasonable compensation mechanism for VK, namely compensation with the third-nearest Hi neighbor from VK for the paraelectric (PE) phase and compensation with the fourth-nearest neighbor Hi from VK for the ferroelectric (FE) phase. The defect formation energies indicate that the [Formula: see text] (The superscript represents the charged state, the 'x' represents neutral, ''' represents -1 charge state and '.' represents +1 charge state.) is the main defect type in this kind of defect cluster and a self-trapped electron is located at Hi in the (VK + Hi)' system. For [Formula: see text] system, one electron is accommodated in VK. There is not a new defect state in the band gap. The Hi bonds with the O ion (0.99 Å) form a hydroxyl. For (VK + Hi)' system, the hydroxyl is broken, the Hi exists in an atomic form and introduces new defect states in the band gap. As the large relaxation energy leads to a large Huang-Rhys factor, the Stokes red shifts will significantly affect the optical properties. A broad ultraviolet (UV) absorption band and emission band range from UV to visible are obtained originating from the defect cluster. We believe that the far-violet absorption peaks (167 nm and 179 nm) caused by defect cluster VK+Hi can significantly impact the optical damage threshold of the KDP.

Redundant potassium transporter systems guarantee the survival of Enterococcus faecalis under stress conditions.

Enterococcus is able to grow in media at pH from 5.0 to 9.0 and a high concentration of NaCl (8%). The ability to respond to these extreme conditions requires the rapid movement of three critical ions: proton (H+), sodium (Na+), and potassium (K+). The activity of the proton F0F1 ATPase and the sodium Na+ V0V1 type ATPase under acidic or alkaline conditions, respectively, is well established in these microorganisms. The potassium uptake transporters KtrI and KtrII were described in Enterococcus hirae, which were associated with growth in acidic and alkaline conditions, respectively. In Enterococcus faecalis, the presence of the Kdp (potassium ATPase) system was early established. However, the homeostasis of potassium in this microorganism is not completely explored. In this study, we demonstrate that Kup and KimA are high-affinity potassium transporters, and the inactivation of these genes in E. faecalis JH2-2 (a Kdp laboratory natural deficient strain) had no effect on the growth parameters. However, in KtrA defective strains (ΔktrA, ΔkupΔktrA) an impaired growth was observed under stress conditions, which was restored to wild type levels by external addition of K+ ions. Among the multiplicity of potassium transporters identify in the genus Enterococcus, Ktr channels (KtrAB and KtrAD), and Kup family symporters (Kup and KimA) are present and may contribute to the particular resistance of these microorganisms to different stress conditions. In addition, we found that the presence of the Kdp system in E. faecalis is strain-dependent, and this transporter is enriched in strains of clinical origin as compared to environmental, commensal, or food isolates.

Fractal Analysis on Machined Surface Morphologies of Soft-Brittle KDP Crystals Processed by Micro Ball-End Milling.

The micro-defects on KH2PO4 (KDP) optic surfaces are mainly repaired by the micro-milling technique, while it is very easy to introduce brittle cracks on repaired surfaces, as KDP is soft and brittle. To estimate machined surface morphologies, the conventional method is surface roughness, but it fails to distinguish ductile-regime machining from brittle-regime machining directly. To achieve this objective, it is of great significance to explore new evaluation methods to further characterize machined surface morphologies. In this study, the fractal dimension (FD) was introduced to characterize the surface morphologies of soft-brittle KDP crystals machined by micro bell-end milling. The 3D and 2D fractal dimensions of the machined surfaces and their typical cross-sectional contours have been calculated, respectively, based on Box-counting methods, and were further discussed comprehensively by combining the analysis of surface quality and textures. The 3D FD is identified to have a negative correlation with surface roughness (Sa and Sq), meaning the worse the surface quality the smaller the FD. The circumferential 2D FD could quantitively characterize the anisotropy of micro-milled surfaces, which could not be analyzed by surface roughness. Normally, there is obvious symmetry of 2D FD and anisotropy on the micro ball-end milled surfaces generated by ductile-regime machining. However, once the 2D FD is distributed asymmetrically and the anisotropy becomes weaker, the assessed surface contours would be occupied by brittle cracks and fractures, and corresponding machining processes will be in a brittle regime. This fractal analysis would facilitate the accurate and efficient evaluation of the repaired KDP optics by micro-milling.

Effect of Wetting Characteristics of Polishing Fluid on the Quality of Water-Dissolution Polishing of KDP Crystals.

KDP crystals constitute the only laser-frequency conversion and electro-optical switches that can be used in laser systems for inertial confinement fusion. However, KDP crystals are difficult to produce because of their inherent softness, brittleness, water-solubility, and temperature sensitivity. The authors' group developed a water-dissolution polishing method in previous studies to obtain near-damage-free KDP surfaces. In this article, the effect of the wetting characteristics of the water dissolution polishing fluid on the crystal surface-a factor rarely considered in the usual process optimization-on the polished surface quality was comprehensively studied. The mean radius of micro water droplets at 5 wt.% and 7.5 wt.% water content was approximately 0.6 nm and 1.2 nm, respectively. Theoretically, the smaller micro water droplet size is beneficial to the polished surface quality. When the water content was 5 wt.%, due to the poor wetting characteristics of the polishing fluid, surface scratches appeared on the polished surface; when the water content was 7.5 wt.%, the effects of the wetting characteristics and the radius of the micro water droplets reached a balance, and the polished surface quality was the best (Ra 1.260 nm). These results confirm that the wetting characteristics of the polishing fluid constitute one of the key factors that must be considered. This study proves that the wetting characteristics of the polishing fluid should be improved during the optimization process of polishing fluid composition when using oil-based polishing fluids for ultra-precision polishing.

Effect of Pre-Existing Micro-Defects on Cutting Force and Machined Surface Quality Involved in the Ball-End Milling Repairing of Flawed KDP Crystal Surfaces.

When serving in extremely high-power laser conditions, KH2PO4 (KDP) surfaces are susceptible to incur laser damage points (also known as defects). Using micro-ball end milling cutters to repair and remove the pre-existing damage points on the flawed KDP crystal surface is the most effective method to control the growth of laser damage points on KDP crystal surfaces and prolong their service life. However, there are various forms of micro-defects (such as pits, scratches and brittle fractures) around the laser damage points on KDP crystal surfaces which possess remarkable effects on the micro-milling repair process and consequently deteriorate the repair quality. In this work, combined with nano-indentation experiments, elastic-plastic mechanics and fracture mechanics theory, a constitutive model considering the anisotropic property of KDP crystals and a three-dimensional (3D) finite element model (FEM) were established to simulate the cutting force and surface topography involved in the ball-end milling repairing of flawed KDP crystal surfaces. Besides, the micro-milling experiments were conducted to evaluate the change of cutting force and machined surface quality in the presence of micro-defects with various feed rates. The results show that micro-defects would induce the fluctuation of cutting force and a change of the undeformed cutting thickness (UCT) in the process of repairing the damage points on the crystal surface, which would lead to the brittle-ductile transition (BDT) and affect the machined surface quality. The machined surface quality was found to be deteriorated by the pre-existing micro-defects when the UCT was small (the UCT was less than 375 nm). On the contrary, brittle mode cutting in the local area can be transformed into ductile mode cutting, resulting in an improvement of repaired surface quality that is exhibited by the cutting force and microtopography. This work has great theoretical significance and engineering practical value for the promotion and application of micro-milling repairing technology in the practical manufacturing and operation of KDP optics applied to high-power laser systems.

KDP, a Lactobacilli Product from Kimchi, Enhances Mucosal Immunity by Increasing Secretory IgA in Mice and Exhibits Antimicrobial Activity.

The potential of KDP, a lactic acid bacterial strain of Lactobacillus sakei, to enhance the production of mucosal specific immunoglobulin A (IgA) in mice and thereby enhance gut mucosal immunity was examined. KDP is composed of dead cells isolated from the Korean traditional food kimchi. Female BALB/c mice orally received 0.25 mg KDP once daily for 5 weeks and were co-administrated ovalbumin (OVA) for negative control and cholera toxin for positive control. Mice administered KDP exhibited increased secretory IgA (sIgA) contents in the small intestine, Peyer's patches, serum, colon, and lungs as examined by ELISA. KDP also significantly increased the gene expression of Bcl-6, IL-10, IL-12p40, IL-21, and STAT4. In addition, KDP acted as a potent antioxidant, as indicated by its significant inhibitory effects in the range of 16.5-59.4% for DPPH, nitric oxide, maximum total antioxidant capacity, and maximum reducing power. Finally, KDP exhibited potent antimicrobial activity as evidenced by a significant decrease in the growth of 7 samples of gram-negative and gram-positive bacteria and Candida albicans. KDP's adjuvant effect is shown to be comparable to that of cholera toxin. We conclude that KDP can significantly enhance the intestine's secretory immunity to OVA, as well as act as a potent antioxidant and antimicrobial agent. These results suggest that orally administered KDP should be studied in clinical trials for antigen-specific IgA production.

Precise Measurements of the Quadratic Electro-Optic Effect in KH2PO4 Crystals Using a Sénarmont-Type System.

This paper presents precise measurements of the temperature dependencies of the quadratic electro-optic coefficients g1111-g1122 and ne3g3333-no3g1133 in KH2PO4 crystals. In addition to traditional electro-optic coefficients describing changes in the function of an applied electric field, intrinsic coefficients, defined in terms of induced polarization, are also considered. Both intrinsic coefficients decrease with increases in temperature, but the relative temperature changes are of different orders of magnitude: 10-4 and 10-3 K-1. A Sénarmont-type setup was used for the electro-optic measurements. To achieve the best accuracy, a new approach was developed, in which, instead of using only one specific point on the modulator's transmission characteristic, the operating point is changed during the measurements.

The Strain Rate Sensitivity and Creep Behavior for the Tripler Plane of Potassium Dihydrogen Phosphate Crystal by Nanoindentation.

As an excellent multifunctional single crystal, potassium dihydrogen phosphate (KDP) is a well-known, difficult-to-process material for its soft-brittle and deliquescent nature. The surface mechanical properties are critical to the machining process; however, the characteristics of deformation behavior for KDP crystals have not been well studied. In this work, the strain rate effect on hardness was investigated on the mechanically polished tripler plane of a KDP crystal relying on nanoindentation technology. By increasing the strain rate from 0.001 to 0.1 s-1, hardness increased from 1.67 to 2.07 GPa. Hence, the strain rate sensitivity was determined as 0.053, and the activation volume of dislocation nucleation was 169 Å3. Based on the constant load-holding method, creep deformation was studied at various holding depths at room temperature. Under the spherical tip, creep deformation could be greatly enhanced with increasing holding depth, which was mainly due to the enlarged holding strain. Under the self-similar Berkovich indenter, creep strain could be reduced at a deeper location. Such an indentation size effect on creep deformation was firstly reported for KDP crystals. The strain rate sensitivity of the steady-state creep flow was estimated, and the creep mechanism was qualitatively discussed.

Interaction Mechanism of Thermal and Mechanical Field in KDP Fly-Cutting Process.

As an important nonlinear optical material, potassium dihydrogen phosphate (KDP) crystal is used in high-power laser beams as the core element of inertial confinement fusion. It is the most general method of single point diamond fly-cutting (SPDF) to produce high precision and crack-free KDP surfaces. Nevertheless, the cutting mechanism of such material remains unclear, and therefore needs further analysis. Firstly, the stress field, cutting force and cutting temperature under different working conditions are calculated by a KDP crystal cutting simulation model. Then, the rules and the cause of change and interaction mechanisms of force and temperature are analyzed by comparing the measurement experiments with simulations. Furthermore, the causes of chip formation and micro-cracks on the machined surface are analyzed based on thermo-mechanical coupling and chip morphology. The conclusion can be deduced: Although the temperature has not reached the phase transition temperature during the finishing process, under high cutting speeds and large unformed chip thickness, such as semi-finishing and roughing, the temperature can reach up to 180 °C or higher, and KDP crystals are very likely to phase transition-chip morphology also verifies this phenomenon.

The micro-wear mechanism of diamond during diamond tool fly-cutting KDP (KH2PO4) from first principle calculations.

First principle calculations were used to study micro-wear mechanism of diamond when diamond fly-cutting was performed on KDP (KH2PO4). Since the (001) surface of KDP is the relatively stable surface by analyzing the chemical bonds and surface energies, we choose the (001) surface of KDP to build the KDP/C interfaced models and KDP/C co-crystal model. According to the populations of interaction models, we can find that the preferential reaction between C and O/P atoms lead to the wear of tool.

Morphological Analysis of KDP-Crystal Workpiece Surfaces Machined by Ultra-Precision Fly Cutting.

Potassium dihydrogen phosphate crystals exhibit excellent nonlinear optical properties that are significantly affected by the surface morphology of the crystal. To comprehensively examine and characterize the morphological features of these crystals, the machined surfaces of workpieces are analyzed using wavelet, fractal, and power spectral density (PSD) methods. First, the fractal method is employed to analyze the features of the machined surfaces of different materials and examine the relationship between the surface roughness and fractal dimension of different materials. Then, the morphological anisotropy of the machined surfaces is analyzed using the two-dimensional PSD method. Based on the orientation of the machined surfaces of the workpieces, the tangential waves on the surfaces are analyzed using wavelet-transform and PSD methods. From a frequency-domain perspective, the scales of various influencing factor signals are identified. Additionally, the frequency range of the spindle vibration is determined based on the machining experiment. On this basis, the cause of the machined surface waviness errors is revealed.

Micro Defects on Diamond Tool Cutting Edge Affecting the Ductile-Mode Machining of KDP Crystal.

As a soft-brittle material, the machined surface quality of potassium dihydrogen phosphate (KDP) crystal is heavily affected by the edge quality of the diamond cutting tool. However, nanoscale micro defects inevitably occur on the freshly sharpened tool edge, and the machining mechanism for KDP crystal remains unclear. Therefore, in this work, three types of tool-edge micro defects are classified according to their cross-sections, including the blunt-edge, crescent-edge, and flat-edge micro defects. Moreover, the smoothed particle hydrodynamics (SPH) method is employed to reveal the material removal mechanism of KDP crystal with consideration of different tool-edge micro defects, and the flat-edge micro defects are subdivided into flat edge A (similar to flank wear) and flat edge B (similar to chamfered edge) on the basis of their effects in machining. The simulation results indicate that the surfaces machined by crescent edge and flat edge A are unsmooth with large-size defects due to the disappearance of hydrostatic pressure beneath the cutting edge. As for the blunt edge and flat edge B, the machined surfaces are smooth with a favorable increment of hydrostatic pressure for processing brittle materials, which indicates that a solution to eliminate the tool-edge micro defects is necessary, e.g., the passivation method. For keeping the cutting edge as sharp as possible in removing the tool-edge micro defects completely by passivation, the effect of tool shank depression angles on the geometries of the passivated cutting edge is investigated, and a high-quality cutting edge with a micro chamfered edge is obtained after passivation at a depression angle of 60° and re-sharpening of the rake face. Finally, the tool cutting performance after passivation is validated through fly-cutting experiments of KDP crystal. The chamfered edge can produce the best defect-free surface with the minimum surface roughness.

Effect of KDP-Crystal Material Properties on Surface Morphology in Ultra-Precision Fly Cutting.

To study the effect of material properties on the surface morphology of potassium dihydrogen phosphate (KDP) crystals, an ultra-precision fly cutting machine tool with a single-point diamond tool was used to perform a cutting experiment on (100) crystal plane of the KDP crystal. The elastic modulus, shear modulus, hardness, and dislocation of KDP crystals are taken into the cutting force model by introducing the strain gradient plasticity theory. Since the size effect and dynamic response will affect the surface roughness during ultra-precision machining, the surface roughness of workpieces in ultra-precision fly cutting is hard to predict. Based on the previously established strain gradient plasticity theoretical model, cutting force model, and the dynamic characteristics of the ultra-precision fly cutting system, a surface morphology prediction model under the influence of KDP crystal material properties was established. Finally, the accuracy of the surface morphology prediction model was verified by ultra-precision fly cutting experiments, and identified the frequency range of the characteristic signal caused by the anisotropy of the KDP crystal from the frequency, thereby verifying the KDP crystal material properties has a significant effect on the surface of the machined workpiece roughness.

Rat Models of Human Type 1 Diabetes.

Rat models of human type 1 diabetes have been shown to be of great importance for the elucidation of the mechanisms underlying the development of autoimmune diabetes. The three major well-established spontaneous rat models are the BioBreeding (BB) diabetes-prone rat, the Komeda diabetes-prone (KDP) rat, and the IDDM (LEW.1AR1-iddm) rat. Their distinctive features are described with special reference to their pathology, immunology, and genetics and compared with the situation in patients with type 1 diabetes mellitus. For all three established rat models, a distinctive genetic mutation has been identified that is responsible for the manifestation of the diabetic syndrome in these rat strains.