Supramolecular chemistry of monochiral naphthalenediimides.

Three new N-desymmetrised naphthalenediimides (NDIs) are described, each containing one chiral and one achiral centre. The ability of such 'monochiral' NDIs to self-assemble into hydrogen-bonded helical nanotubes, to act as a sergeant in a 'sergeants-and-soldiers' system and to form a hexameric receptor for C(70) was examined. Small differences at the achiral centre were found to have significant effects on the supramolecular properties of the NDI. All three new NDIs form nanotubes that bind C(60), but with different efficiencies, and one is a better sergeant than any of the dichiral NDIs investigated to date.

The sergeants-and-soldiers effect: chiral amplification in naphthalenediimide nanotubes.

Self-assembling naphthalenediimide (NDI)-based helical organic nanotubes display sergeants-and-soldiers behaviour, chiral monomers imposing a supramolecular structure upon achiral monomers. Several achiral NDI monomers were synthesised and their ability to incorporate into supramolecular nanotubes was studied. Nanotubes containing predominantly the most effective soldier, derived from 1-aminocyclopropane-carboxylic acid, are effective hosts for C(60).

Retrograde flow and myosin II activity within the leading cell edge deliver F-actin to the lamella to seed the formation of graded polarity actomyosin II filament bundles in migrating fibroblasts.

In migrating fibroblasts actomyosin II bundles are graded polarity (GP) bundles, a distinct organization to stress fibers. GP bundles are important for powering cell migration, yet have an unknown mechanism of formation. Electron microscopy and the fate of photobleached marks show actin filaments undergoing retrograde flow in filopodia, and the lamellipodium are structurally and dynamically linked with stationary GP bundles within the lamella. An individual filopodium initially protrudes, but then becomes separated from the tip of the lamellipodium and seeds the formation of a new GP bundle within the lamella. In individual live cells expressing both GFP-myosin II and RFP-actin, myosin II puncta localize to the base of an individual filopodium an average 28 s before the filopodium seeds the formation of a new GP bundle. Associated myosin II is stationary with respect to the substratum in new GP bundles. Inhibition of myosin II motor activity in live cells blocks appearance of new GP bundles in the lamella, without inhibition of cell protrusion in the same timescale. We conclude retrograde F-actin flow and myosin II activity within the leading cell edge delivers F-actin to the lamella to seed the formation of new GP bundles.

Differential proteome analysis of TRAP-activated platelets: involvement of DOK-2 and phosphorylation of RGS proteins.

We have applied a proteomics approach to analyze signaling cascades in human platelets stimulated by thrombin receptor activating peptide (TRAP). By analyzing basal and TRAP-activated platelets using 2-dimensional gel electrophoresis (2-DE), we detected 62 differentially regulated protein features. From these, 41 could be identified by liquid chromatography-coupled tandem mass spectrometry (LC-MS/MS) and were found to derive from 31 different genes, 8 of which had not previously been reported in platelets, including the adapter downstream of tyrosine kinase 2 (Dok-2). Further studies revealed that the change in mobility of Dok-2 was brought about by tyrosine phosphorylation. Dok-2 tyrosine phosphorylation was also found to be involved in collagen receptor, glycoprotein VI (GPVI), signaling as well as in outside-in signaling through the major platelet integrin, alpha IIIb beta 3. These studies also provided the first demonstration of posttranslational modification of 2 regulator of G protein signaling (RGS) proteins, RGS10 and 18. Phosphorylation of RGS18 was mapped to Ser49 by MS/MS analysis. This study provides a new approach for the identification of novel signaling molecules in activated platelets, providing new insights into the mechanisms of platelet activation and building the basis for the development of therapeutic agents for thrombotic diseases.