A Light-Operated Molecular Cable Car for Gated Ion Transport.

Inspired by the nontrivial and controlled movements of molecular machines, we report an azobenzene-based molecular shuttle PR2, which can perform light-gated ion transport across lipid membranes. The amphiphilicity and membrane-spanning molecular length enable PR2 to insert into the bilayer membrane and efficiently transport K+ (EC50 =4.1 µm) through the thermally driven stochastic shuttle motion of the crown ether ring along the axle. The significant difference in shuttling rate between trans-PR2 and cis-PR2 induced by molecular isomerization enables a light-gated ion transport, i.e., ON/OFF in situ regulation of transport activity and single-channel current. This work represents an example of using a photoswitchable molecular machine to realize gated ion transport, which demonstrates the value of molecular machines functioning in biomembranes.

Fabrication of self-assembling D-form peptide nanofiber scaffold d-EAK16 for rapid hemostasis.

We previously reported a class of designer self-assembling peptides that form 3-dimensional nanofiber scaffolds using only l-amino acids. Here we report that using d-amino acids, the chiral self-assembling peptide d-EAK16 also forms 3-dimensional nanofiber scaffold that is indistinguishable from its counterpart l-EAK16. These chiral peptides containing all d-amino acids, d-EAK16, self-assemble into well-ordered nanofibers. However with alternating d- and l-amino acids, EAK16 and EAK16, showed poor self-assembling properties. To fully understand individual molecular building blocks and their structures, assembly properties and dynamic behaviors for rapid hemostasis, we used circular dichroism, atomic force microscopy and scanning electron microscopy to study in detail the peptides. We also used rheological measurement to study the hydrogel gelation property. Furthermore, we used an erythrocyte-agglutination test and a rabbit liver wound healing model, particularly in the transverse rabbit liver experiments, to examine rapid hemostasis. We showed that 1% d-EAK16 for the liver wound hemostasis took ∼20 s, but using 1% of EAK16 and EAK16 that have alternating chiral d- and l-amino acids took ∼70 and ∼80 s, respectively. We here propose a plausible model not only to provide insights in understanding the chiral assembly properties for rapid hemostasis, but also to aid in further design of self-assembling d-form peptide scaffolds for clinical applications.

Temperature and pH effects on biophysical and morphological properties of self-assembling peptide RADA16-I.

It has been found that the self-assembling peptide RADA 16-I forms a beta-sheet structure and self-assembles into nanofibers and scaffolds in favor of cell growth, hemostasis and tissue-injury repair. But its biophysical and morphological properties, especially for its beta-sheet and self-assembling properties in heat- and pH-denatured conditions, remain largely unclear. In order to better understand and design nanobiomaterials, we studied the self-assembly behaviors of RADA16-I using CD and atomic force microscopy (AFM) measurements in various pH and heat-denatured conditions. Here, we report that the peptide, when exposed to pH 1.0 and 4.0, was still able to assume a typical beta-sheet structure and self-assemble into long nanofiber, although its beta-sheet content was dramatically decreased by 10% in a pH 1.0 solution. However, the peptide, when exposed to pH 13.0, drastically lost its beta-sheet structure and assembled into different small-sized globular aggregates. Similarly, the peptide, when heat-denatured from 25 to 70 degrees C, was still able to assume a typical beta-sheet structure with 46% content, but self-assembled into small-sized globular aggregates at much higher temperature. Titration experiments showed that the peptide RADA16-I exists in three types of ionic species: acidic (fully protonated peptide), zwitterionic (electrically neutral peptide carrying partial positive and negative charges) and basic (fully deprotonated peptide) species, called 'super ions'. The unordered structure and beta-turn of these 'super ions' via hydrogen or ionic bonds, and heat Brownian motion under the above denatured conditions would directly affect the stability of the beta-sheet and nanofibers. These results help us in the design of future nanobiomaterials, such as biosensors, based on beta-sheets and environmental changes. These results also help understand the pathogenesis of the beta-sheet-mediated neuronal diseases such as Alzheimer's disease and the mechanism of hemostasis.