Tuning the formation and rupture of single ligand-receptor bonds by hyaluronan-induced repulsion

We used a combination of laminar flow chamber and reflection interference microscopy to study the formation and rupture of single bonds formed between Fc-ICAM-1 attached to a substrate and anti-ICAM-1 carried by micrometric beads in the presence of a repulsive hyaluronan (HA) layer adsorbed onto the substrate. The absolute distance between the colloids and the surface was measured under flow with an accuracy of a few nanometers. We could verify the long-term prediction of classical lubrication theory for the movement of a sphere near a wall in a shear flow. The HA polymer layer exerted long-range repulsive steric force on the beads and the hydrodynamics at the boundary remained more or less unchanged. By incubating HA at various concentrations, the thickness of the layer, as estimated by beads most probable height, was tuned in the range 20-200 nm. Frequency of bond formation was decreased by more than one order of magnitude by increasing the thickness of the repulsive layer, while the lifetime of individual bonds was not affected. This study opens the way for further quantitative studies of the effect of molecular environment and separation distance on ligand-receptor association and dissociation.     

Mesure journaliére sur cycle végétatif complet des échanges gazeux: photosynthése, transpiration et respiration nocturne ďune culture de Maïs conduite sur colonnes de sol

Daily measurement of gas exchanges during a complete growth cycle: photosynthesis, transpiration and night respiration in a soil culture of maize. During a complete growth cycle, photosynthesis (P), night-respiration (R) and transpiration (T) have been measured daily for maize (Zea mays L. cv. INRA F7 × F2) in a self-regulating growth chamber. P and T varied according to three different kinetics. During the growing period there was a fast and concomitant variation of both P and T, which could be filled to a power function of time. During the fructification period we observed a linear decrease of P and T. Finally, during the senescence period P decreased to zero, whereas T kept a value higher than the evaporation of the naked soil. In the first two periods, the P/T ratio decreased as leaves aged. From this we could deduce that a slow increase of stomatal resistance (RS) and mesophyll resistance (RM) took place. R increased until the panicle appeared; it remained constant during fructification and then it decreased with senescence. Each nitrogen supply induced a transient increase of R. Finally, a water stress led to a greater decrease of P than of R, but the after effect of water stress disappeared a day later. These results were compared with those obtained in hydroponic conditions.     

Comparative analysis of the <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> and <Emphasis Type="Italic">Caenorhabditis elegans</Emphasis> protein interaction networks

Background  

Protein interaction networks aim to summarize the complex interplay of proteins in an organism. Early studies suggested that the position of a protein in the network determines its evolutionary rate but there has been considerable disagreement as to what extent other factors, such as protein abundance, modify this reported dependence.