Kinetics of diffusion-mediated DNA hybridization in lipid monolayer films determined by single-molecule fluorescence spectroscopy.

We use single-molecule fluorescence microscopy to monitor individual hybridization reactions between membrane-anchored DNA strands, occurring in nanofluidic lipid monolayer films deposited on Teflon AF substrates. The DNA molecules are labeled with different fluorescent dyes, which make it possible to simultaneously monitor the movements of two different molecular species, thus enabling tracking of both reactants and products. We employ lattice diffusion simulations to determine reaction probabilities upon interaction. The observed hybridization rate of the 40-mer DNA was more than 2-fold higher than that of the 20-mer DNA. Since the lateral diffusion coefficient of the two different constructs is nearly identical, the effective molecule radius determines the overall kinetics. This implies that when two DNA molecules approach each other, hydrogen bonding takes place distal from the place where the DNA is anchored to the surface. Strand closure then propagates bidirectionally through a zipper-like mechanism, eventually bringing the lipid anchors together. Comparison with hybridization rates for corresponding DNA sequences in solution reveals that hybridization rates are lower for the lipid-anchored strands and that the dependence on strand length is stronger

AH Peptide-Mediated Formation of Charged Planar Lipid Bilayers

Planar lipid bilayers on solid supports provide a controllable platform to mimic biological membranes. Adsorption and spontaneous rupture of vesicles is the most common method to form planar bilayers. While many substrates support vesicle adsorption, vesicles rupture spontaneously on only a few materials. In order to form planar bilayers on materials intractable to conventional vesicle fusion, an amphipathic, α-helical (AH) peptide has been identified that can rupture adsorbed vesicles and form planar bilayers on previously intractable materials. Most studies using AH peptide have employed zwitterionic lipid compositions only, and the range of suitable lipid compositions remains to be elucidated. Herein, using quartz crystal microbalance-dissipation and ellipsometry, we investigated the effects of membrane surface charge on AH peptide-mediated bilayer formation via the rupture of surface-adsorbed vesicles on titanium oxide. Our findings demonstrate that AH peptide can promote the formation of positively and negatively charged bilayers. Importantly, the kinetics of vesicle rupture by AH peptide are strongly influenced by the membrane surface charge. Although the titanium oxide surface is negatively charged, the formation of negatively charged bilayers was quickest among the tested lipid compositions. Taken together, the experimental data supports that the effects of membrane surface charge on the rupture kinetics are related to variations in the extent of vesicle destabilization prior to vesicle rupture. Given the wide range of lipid compositions amenable to AH peptide-mediated vesicle rupture, this work further suggests that AH peptide is largely unique among membrane-active peptides, thereby substantiating its position as a promising broad-spectrum antiviral agent.NRF (Natl Research Foundation, S’pore)NMRC (Natl Medical Research Council, S’pore

SDSS J211852.96−073227.5: The first non-local, interacting, late-type intermediate Seyfert galaxy with relativistic jets

It has been often suggested that a tangible relation exists between relativistic jets in active galactic nuclei (AGN) and the morphology of their host galaxies. In particular, relativistic jets may commonly be related to merging events. Here we present for the first time a detailed spectroscopic and morphological analysis of a Seyfert galaxy, SDSS J211852.96−073227.5, at z = 0.26. This source has previously been classified as a gamma-ray emitting narrow-line Seyfert 1 galaxy. We re-observed it with the 6.5 m Clay Telescope and these new, high-quality spectroscopic data have revealed that it is actually an intermediate-type Seyfert galaxy. Furthermore, the results of modelling the Ks-band near-infrared images obtained with the 6.5 m Baade Telescope indicate that the AGN is hosted by a late-type galaxy in an interacting system, strengthening the suggested connection between galaxy interactions and relativistic jets