Antibody-bearing liposomes improve agglutination of latex particles used in clinical diagnostic assays

Ligand-bearing liposomes are used to enhance the agglutination ‘signal’ of a typical latex assay for the detection of human rheumatoid factor. Heat-denatured IgG, the antigen to which rheumatoid factor binds naturally, was covalently attached to latex spheres. The liposomes were covalently coated with a ‘second ligand’ which also recognizes rheumatoid factor, anti-human IgM Fab′ fragments. In the present test configuration, rheumatoid factor present in a patient's serum binds to the IgG attached to the latex particles. The liposomes, in turn, bind rapidly to rheumatoid factor-sensitized latex, via the second ligand, promoting the formation of large, clearly visible latex aggregates. When latex spheres bearing the same type and density of second ligand were used to replace the liposomes they failed to improve agglutination, suggesting that multivalent presentation of the second ligand is not sufficient to insure the improvement. These results suggest that fluidity of the liposomal membrane is a requirement for the effect. Sensitivity as well as ‘readability’ are improved by the liposomes while specificity remains unaffected. The principle of using ligand-bearing liposomes to enhance particle agglutination is applicable to a wide range of other diagnostic assays.     

Chromatin phospholipids and DNA synthesis in hepatic cells

The synthesis of phospholipids found in microsomes, in the nuclei and in chromatin has been studied in rat liver after partial hepatectomy. [32P]O4(2-)incorporation in phospholipids has been compared with that of (3H) thymidine over a period of 48 h after operation. The presence of two peaks of DNA synthesis has been observed at 18 and 36 h; nuclear phospholipids show a continuous synthesis starting from 12 h, whereas the microsomes show two peaks at 12 and 24-30 h. The specific activity of the chromatin phospholipid fraction increases at 12h, doubles its initial value at 18 h, shows a peak at 30 h and comes back to the initial value at 48 h. It is concluded that chromatin phospholipids increase their synthesis in relation to the S phase of the cell cycle, whereas those of the nuclear membranes do not change the rate of synthesis throughout the cell cycle. The possibility is suggested that chromatin phospholipids are synthesized in the microsomes and transferred to the nucleus.     

Assay to mechanically tune and optically probe fibrillar fibronectin conformations from fully relaxed to breakage

In response to growing needs for quantitative biochemical and cellular assays that address whether the extracellular matrix (ECM) acts as a mechanochemical signal converter to co-regulate cellular mechanotransduction processes, a new assay is presented where plasma fibronectin fibers are manually deposited onto elastic sheets, while force-induced changes in protein conformation are monitored by fluorescence resonance energy transfer (FRET). Fully relaxed assay fibers can be stretched at least 5-6 fold, which involves Fn domain unfolding, before the fibers break. In native fibroblast ECM, this full range of stretch-regulated conformations coexists in every field of view confirming that the assay fibers are physiologically relevant model systems. Since alterations of protein function will directly correlate with their extension in response to force, the FRET vs. strain curves presented herein enable the mapping of fibronectin strain distributions in 2D and 3D cell cultures with high spatial resolution. Finally, cryptic sites for fibronectin's N-terminal 70-kD fragment were found to be exposed at relatively low strain, demonstrating the assay's potential to analyze stretch-regulated protein-protein interactions.     

Dynamic BTPS correction factors for spirometric data

Because it is often difficult to completely control ambient temperature, a study was conducted to investigate dynamic body temperature pressure saturated (BTPS) correction factors for spirometric data. A forced expiratory simulator system was heated to 37 degrees C and loaded with air saturated with water vapor. This air was then forced from the simulator into a dry rolling-seal spirometer maintained at various ambient temperatures from 3 to 32 degrees C. Errors in forced expiratory volume in 1 s (FEV1) and peak flow from assuming a constant BTPS correction ranged from 7.7 and 14.1% at 3 degrees C to 2.1 and 4.6% at 23 degrees C. Differences between errors observed when saturated and dry air were forced into the spirometer indicate that water vapor condensation introduces an added heat load to the spirometer, adding approximately one percent to the error in FEV1 at lower temperatures. By use of a model to estimate the dynamic BTPS correction factor, errors in FEV1 at all temperatures between 3 and 32 degrees C were reduced to less than 1.5%.     

Periaxonal and nodal plasticities modulate action potential conduction in the adult mouse brain

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机械力作用下蛋白质结构和功能的转换

机械力作用下蛋白质结构和功能的转换涉及到纳米尺度范围内机械化学信号之间的转换。本文从以下几个方面对这一领域进行了综述：局部外力和几何感觉控制细胞功能：多结构域蛋白——纤连素在机械转化中的优点：将外力转化成生化信号;活细胞中细胞外基质中的纤连素在力诱导下的展开;纤连素Ⅲ型结构域通过序列变化调节机械稳定性：大肠杆菌Ⅰ型毛缘的展开结构有利于捕获键形成以及在药物和技术领域的应用。     

Experimental and genetic analysis of root development inArabidopsis thaliana

The cellular organisation of theArabidopsis thaliana root is remarkably regular. A fate map of the primary root and root meristem that predicts the developmental destinies of cells within the embryonic root primordium has been constructed. Nevertheless, laser ablation experiments demonstrate that root meristem cells develop according to position and not according to lineage. Mutational analysis has identified genes required for cell specification in the radial as well as in the apical-basal dimension. The corresponding gene functions appear to be necessary during embryogenesis for the formation of a correctly patterned primary root. H Lambers Section editor     

A structural model for force regulated integrin binding to fibronectin's RGD-synergy site.

The synergy site on fibronectin's FN-III(9) module, located approximately 32 A away from the RGD-loop on FN-III(10), greatly enhances integrin alpha(5)beta(1) mediated cell binding. Since fibronectin is exposed to mechanical forces acting on the extracellular matrix in vivo, we used steered molecular dynamics to study how mechanical stretching of FN-III(9-10) affects the relative distance between these two synergistic sites. Our simulations predict the existence of an intermediate state prior to unfolding. In this state, the synergy-RGD distance is increased from 32 A to approximately 55 A, while the conformations of both sites remain unperturbed. This distance is too large for both sites to co-bind the same receptor, as indicated by experiments that confirm that increasing the length of the linker chain between FN-III(9) and FN-III(10) reduces alpha(5)beta(1) binding. Our simulations thus suggest that increased alpha(5)beta(1)-binding attributed to the synergy site, along with the associated downstream cell-signaling events, can be turned off mechanically by stretching FN-III(9-10) into this intermediate state. The potential physiological implications are discussed.