An X-ray diffraction study on a single rod outer segment from frog retina

X-ray diffraction patterns were recorded from isolated single rod outer segments of frog. The outer segments in Ringer's solution were exposed to a 6 µm microbeam (15 keV) at the BL40XU beamline, SPring-8. The diffraction pattern demonstrated a remarkable regularity in the stacking and flatness of the disk membranes. The electron density profile calculated from the intensity of up to tenth-order reflections showed a pair of bilayers that comprise a disk membrane. The structure of the disk membrane and the changes in the profile on swelling generally agreed with previous reports. Radiation damage was significant with an irradiation of 5 × 10(5) Gy which is much lower than the known damaging dose on proteins at the liquid-nitrogen temperature.

Aspect-ratio-dependent phase transitions and concentration fluctuations in aqueous colloidal dispersions of charged platelike particles

Phase transitions of aqueous colloidal dispersions of charged platelike particles of niobate nanosheets were investigated as a function of the aspect ratio (r(asp)) and particle volume concentration (φ(p)) by means of small-angle neutron scattering and small-angle x-ray scattering. The results elucidated the following three pieces of evidence: (1) the macroscopic phase separation of the dispersions into an isotropic phase and a liquid crystalline (LC) phase under the conditions of (a) varying r(asp) (1.3×10(-4) ≤ r(asp) ≤ 2.5×10(-3)) at a constant φ(p) = 0.01 and (b) varying φ(p) (0.01 ≤ φ(p) ≤ 0.025) at a constant r(asp) = 2.5×10(-3), a mechanism of which is proposed in the text, where r(asp) ≡ d/ ̅L, with d and ̅L being thickness and the average lateral size of the plates, respectively; (2) the r(asp)-induced phase transition of the LC phase from a nematic phase to a highly periodic layered phase, the line shapes of the scattering peaks of which were examined by Caillé's analysis, upon increasing r(asp) under the condition (a); (3) the LC phase having remarkable concentration fluctuations of the particles which are totally unexpected for the conventional lyotropic molecular LC but which are anticipated to be general for the platelike colloidal particles.

Knocking-in the R142C mutation in transglutaminase 1 disrupts the stratum corneum barrier and postnatal survival of mice

BACKGROUND

Mutations in the gene encoding transglutaminase 1 (TG1) are responsible for various types of autosomal recessive congenital ichthyosis (ARCI), such as lamellar ichthyosis (LI), congenital ichthyosiform erythroderma (CIE) and some minor variants of ARCI. A point mutation of R143C in the β-sandwich domain of TG1 has been often identified in patients with LI or CIE.

OBJECTIVE

To elucidate the effect of that point mutation on skin barrier structures and functions, we generated mice with a point mutation of R142C, which corresponds to the R143C mutation in human TG1.

METHODS

A mouse line with the R142C point mutation in TG1 was established using a gene targeting technique and the Cre-loxP system. The skin phenotypes were analyzed in homozygous mutant Tgm1(R142C/R142C) mice.

RESULTS

In the skin of Tgm1(R142C/R142C) mice, expression of the mutant transcripts was comparable with wild-type or Tgm1(+/R142C) mice. However, the amount of mutated protein in the skin was markedly decreased in Tgm1(R142C/R142C) mice, and the TG1 activity of Tgm1(R142C/R142C) keratinocytes was almost lost. Tgm1(R142C/R142C) mice exhibited morphological and functional skin barrier defects and neonatal lethality. The stratum corneum of those mice lacked cornified envelopes, and loricrin, the major structural component, failed to assemble at the corneocyte cell periphery. Tgm1(R142C/R142C) mice showed a marked increase in transepidermal water loss and their skin was easily permeable to toluidine blue dye. The intercellular lipid lamellar structures of the stratum corneum were irregular and the 13-nm periodic X-ray diffractions from the stratum corneum lipid molecules were lost in vivo.

CONCLUSION

From these results, we suggest that the R142C mutation of TG1 reduces the enzyme stability which is indispensable for development of the stratum corneum and skin barrier function and for postnatal survival of mice.

Kinetics of low pH-induced lamellar to bicontinuous cubic phase transition in dioleoylphosphatidylserine∕monoolein

Recently, it has been well recognized that the modulation of electrostatic interactions due to surface charges can induce transitions between lamellar liquid-crystalline (L(α)) and inverse bicontinuous double-diamond cubic (Q(II)(D)) phases in biological lipids. To reveal their kinetic pathway and mechanism, we investigated the low pH-induced L(α) to Q(II)(D) phase transitions in 20%-dioleoylphosphatidylserine (DOPS)/80%-monoolein (MO) using time-resolved small-angle x-ray scattering and a rapid mixing method. At a final pH of 2.6-2.9, the L(α) phase was transformed completely into the hexagonal II (H(II)) phase within 2-10 s after mixing a low pH buffer with a suspension of multilamellar vesicles of 20%-DOPS∕80%-MO (the initial step). Subsequently, the H(II) phase slowly converted into the Q(II)(D) phase and completely disappeared within 15-30 min (the second step). The rate constants of the second step were obtained using the singular value decomposition analysis. On the basis of these data, we discuss the underlying mechanism of the kinetic pathway of the low pH-induced L(α) to Q(II)(D) phase transitions.

Loop-mediated isothermal amplification assay for detection and discrimination of Toxocara canis and Toxocara cati eggs directly from sand samples

We developed a novel and simple method, using loop-mediated isothermal amplification (LAMP), for the detection and discrimination of Toxocara canis and Toxocara cati eggs. The new method employs 4 steps: (1) concentration of Toxocara eggs in a small amount of sand; (2) dissolution of the proteinaceous membrane of eggs and simultaneously separation of them from the sand using NaClO treatment; (3) extraction of DNA using NaOH treatment; and (4) detection of T. canis / T. cati DNA using a LAMP assay. All these steps are fast, easy to perform, and do not require expensive equipment or reagents. The novel method was tested both experimentally and in a field study. In the laboratory, we could reliably detect as few as 3 T. canis eggs in artificially contaminated sand, if the experiment was repeated twice. In the field trial, we were able to detect T. cati DNA from 4 natural sandpits having moderate to heavy contamination, although not in a single lightly contaminated sandpit. All of the examined sandpits were found to be contaminated with eggs of T. cati, but none appeared to contain T. canis. Our new method could extract DNA from T. canis and T. cati eggs directly from sand samples as well as detect and distinguish these 2 species in a few easy steps, with markedly reduced time and expense.

Formation mechanism studies of phenylene-bridged periodic mesoporous organosilicas (PMOs)

The formation of phenylene-bridged periodic mesoporous organosilicas (PMOs) in the presence of three diblock copolymers differing in hydrophobic hydrocarbon chain lengths was investigated. Hexaethylene glycol octadecylether (C(18)(EO)(6)), hexaethylene glycol hexadecylether (C(16)(EO)(6)), and hexaethylene glycol dodecylether (C(12)(EO)(6)) were chosen in order to obtain insight on the influence of the hydrocarbon chain length on the mesostructure. 1,4-Bis(triethoxysilyl)benzene (BTEB) was used as organosilica precursor under mild acidic conditions. The reactions were followed by in situ small-angle X-ray diffraction (SAXD) on-time in a capillary flow setup. It was found that during the reaction the formation of different structures was observed, which is ascribed to the hydrolysis and condensation of the organosilica precursor. In all cases, different structures evolve with time and phase transitions are observed during the measurements independent of the hydrocarbon chain length.

Structure of amyloid fibrils of hen egg white lysozyme studied by microbeam X-ray diffraction

Structure of spherical aggregates formed by hen egg white lysozyme (HEWL) was studied with microbeam X-ray diffraction. Aggregates with a diameter of 50-100 microm were formed after incubation of HEWL at pH 1.6 and 60 degrees C up to 60 days. The scattering from the aggregate in solution showed a marked symmetry demonstrating it as a spherulite. A reflection at 1/0.46 nm(-1) along the fiber axis showed the presence of beta-sheets along the fiber. There were strong equatorial reflections at 1/2.4 and 1/1.2 nm(-1). The similarities to other amyloid fibers suggest that molecules are planar in the direction perpendicular to the fiber axis and beta-strands are making hydrogen bonds to neighboring molecules.

Evaluation of enamel crystallites in subsurface lesion by microbeam X-ray diffraction

Early caries lesion is a demineralization process that takes place in the top 0.1 mm layer of tooth enamel. In this study, X-ray microbeam diffraction was used to evaluate the hydroxyapatite crystallites in the subsurface lesion of a bovine enamel section and the results are compared with those obtained by transversal microradiography, a method commonly used for evaluation of tooth mineral. Synchrotron radiation from SPring-8 was used to obtain a microbeam with a diameter of 6 microm. Wide-angle X-ray diffraction reports the amount of hydroxyapatite crystals, and small-angle X-ray scattering reports that of voids in crystallites. All three methods showed a marked decrease in the enamel density in the subsurface region after demineralization. As these diffraction methods provide structural information in the nanometre range, they are useful for investigating the mechanism of the mineral loss in early caries lesion at a nanometre level.

Trypanosoma bruceivacuolar protein sorting 41 (VPS41) is required for intracellular iron utilization and maintenance of normal cellular morphology

Procyclic forms ofTrypanosoma brucei bruceiremain and propagate in the midgut of tsetse fly where iron is rich. Additional iron is also required for their growth inin vitroculture. However, little is known about the genes involved in iron metabolism and the mechanism of iron utilization in procyclic-form cells. Therefore, we surveyed the genes involved in iron metabolism in theT. b. bruceigenome sequence database. We found a potential homologue of vacuole protein sorting 41 (VPS41), a gene that is required for high-affinity iron transport inSaccharomyces cerevisiaeand cloned the full-length gene (TbVPS41). Complementation analysis of TbVPS41 in ΔScvps41yeast cells showed that TbVPS41 could partially suppress the inability of ΔScvps41yeast cells to grow on low-iron medium, but it could not suppress the fragmented vacuole phenotype. Further RNA interference (RNAi)-mediated gene knock-down in procyclic-form cells resulted in a significant reduction of growth in low-iron medium; however, no change in growth was observed in normal culture medium. Transmission electron microscopy showed that RNAi causedT. b. bruceicells to have larger numbers of small intracellular vesicles, similar to the fragmented vacuoles observed in ΔScvps41yeast cells. The present study demonstrates that TbVPS41 plays an important role in the intracellular iron utilization system as well as in the maintenance of normal cellular morphology.