Although significant efforts were devoted to improving the properties of conductive polymers, the effects of solvent and supporting electrolytes on the morphology and electrochromic features of electropolymerized materials have been scantly investigated. In this work, the effects of the polymerization conditions, such as the solvents and supporting electrolytes, on the morphological structure and electrochromic properties of PEDOT films were systematically studied. Surprisingly, we find a very significant solvent effect and a small supporting electrolyte effect. We show that morphological properties also strongly correlate with electrochromic properties. Films prepared in propylene carbonate have a smoother structure than those prepared in acetonitrile and this leads to superior electrochromic properties, such as an exceptionally high contrast ratio (71%), transparency in the doped state (80%), and coloration efficiency (193 cm 2 /C) for the films prepared in propylene carbonate. Significant differences between propylene carbonate and acetonitrile were explained by different solubilities of EDOT oligomers produced during initial stages of electropolymerization in these solvents.

Cell membrane fluctuations (CMF) of human erythrocytes, measured by point dark field microscopy, were shown to depend, to a large extent, on intracellular MgATP (Levin, S.V., and R. Korenstein. 1991. Biophys. J. 60:733–737). The present study extends that investigation and associates CMF with F-actin's ATPase activity. MgATP was found to reconstitute CMF in red blood cell (RBC) ghosts and RBC skeletons to their levels in intact RBCs, with an apparent K d of 0.29 mM. However, neither non-hydrolyzable ATP analogues (AMP-PNP, ATPγS) nor hydrolyzable ones (ITP, GTP), were able to elevate CMF levels. The inhibition of ATPase activity associated with the RBC's skeleton, carried out either by the omission of the MgATP substrate or by the use of several inhibitors (vanadate, phalloidin, and DNase I), resulted in a strong decrease of CMF. We suggest that the actin's ATPase, located at the pointed end of the short actin filament, is responsible for the MgATP stimulation of CMF in RBCs.

Extracellular f luid macroviscosity (EFM), modified by macromolecular cosolvents as occurs in body f luids, has been shown to affect cell membrane protein activities but not isolated proteins. In search for the mechanism of this phenomenon, we examined the effect of EFM on mechanical f luctuations of the cell membrane of human erythrocytes. The macroviscosity of the external medium was varied by adding to it various macromolecules [dextrans (70, 500, and 2,000 kDa), polyethylene glycol (20 kDa), and carboxymethyl-cellulose (100 kDa)], which differ in size, chemical nature, and in their capacity to increase f luid viscosity. The parameters of cell membrane f luctuations (maximal amplitude and half-width of amplitude distribution) were diminished with the elevation of solvent macroviscosity, regardless of the cosolvent used to increase EFM. Because thermally driven membrane f luctuations cannot be damped by elevation of EFM, the existence of a metabolic driving force is suggested. This is supported by the finding that in ATPdepleted red blood cells elevation of EMF did not affect cell membrane f luctuations. This study demonstrates that (i) EFM is a regulator of membrane dynamics, providing a possible mechanism by which EFM affects cell membrane activities; and (ii) cell membrane f luctuations are driven by a metabolic driving force in addition to the thermal one.The viscosity of body fluids is determined by the level of macromolecules consisting of proteins, lipoproteins, and polysacharides (1). Accordingly, elevated plasma viscosity has been observed in various diseases associated with increased levels of proteins and lipoproteins, such as diabetes, hyperlipidemia, macroglobulinemia, multiple myeloma, nephrosis, and others (1-5). Various studies have shown that solvent viscosity affects protein dynamics and reactions (6-10). However, in these studies the solvent viscosity was modified by the addition of high concentrations of small cosolvents such as glycerol and sucrose, producing relatively high viscosity levels. This is incompatible with physiological and pathological states, where fluid viscosity is altered by small concentrations of large macromolecules (1). Other studies, in which the viscosity was elevated by macromolecular cosolvents, have shown that extracellular fluid macroviscosity (EFM) is a regulator of cellular processes, such as secretion of renin (11) and lipoproteins (12), phospholipase A 2 activity at the cell membrane (13, 14), and ganglioside metabolism (15). In search of the mechanism of this phenomenon, the effect of macroviscosity, as modified by macromolecules, on isolated proteins in aqueous solutions was examined (16,17). It was found that the effect of solvent viscosity decreases with increasing molecular weight of the cosolvent and is practically diminished when the cosolvent molecular weight exceeds that of the protein. Because the activity of cell membrane enzymes is known to be sensitive to the physical properties of the membrane (18), we considered the possibility that the...

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RIP opens a new perspective in anti-S. aureus prophylaxis, particularly in dialysis patients.

Enzymatic processing of extracellular matrix (ECM) macromolecules by matrix metalloproteases (MMPs) is crucial in mediating physiological and pathological cell processes. However, the molecular mechanisms leading to effective physiological enzyme-ECM interactions remain elusive. Only scant information is available on the mode by which matrix proteases degrade ECM substrates. An example is the enzymatic degradation of triple helical collagen II fragments, generated by the collagenase MMP-8 cleavage, during the course of acute inflammatory conditions by gelatinase B/MMP-9. As is the case for many other matrix proteases, it is not clear how MMP-9 recognizes, binds and digests collagen in this important physiological process. We used single molecule imaging to directly visualize this protease during its interaction with collagen fragments. We show that the initial binding is mediated by the diffusion of the protease along the ordered helix on the collagen ¾ fragment, with preferential binding of the collagen tail. As the reaction progressed and prior to collagen degradation, gelatin-like morphologies resulting from the denaturation of the triple helical collagen were observed. Remarkably, this activity was independent of enzyme proteolysis and was accompanied by significant conformational changes of the working protease. Here we provide the first direct visualization of highly complex mechanisms of macromolecular interactions governing the enzymatic processing of ECM substrates by physiological protease.

Membrane fusion between the human immunodeficiency virus (HIV) and the target cell plasma membrane is correlated with conformational changes in the HIV gp41 glycoprotein, which include an early exposed conformation (prehairpin) and a late low energy six helix bundle (SHB) conformation also termed hairpin. Peptides resembling regions from the exposed prehairpin have been previously studied for their interaction with membranes. Here we report on the expression, purification, SHB stability, and membrane interaction of the full-length ectodomain of the HIV gp41 and its two deletion mutants, all in their SHB-folded state. The interaction of the proteins with zwitterionic and negatively charged membranes was examined by using various biophysical methods including circular dichroism spectroscopy, differential scanning calorimetry, lipid mixing of large unilamellar vesicles, and atomic force microscopy (AFM). All experiments were done in an acidic environment in which the protein remains in its soluble trimeric state. The data reveal that all three proteins fold into a stable coiled-coil core in aqueous solution and retain a stable helical fold with reduced coiled-coil characteristics in a zwitterionic and negatively charged membrane mimetic environment. Furthermore, in contrast with the extended exposed N-terminal domain, the folded gp41 ectodomain does not induce lipid mixing of zwitterionic membranes. However, it disrupts and induces lipid mixing of negatively charged phospholipid membranes (approximately 100-fold more effective than fusion peptide alone), which are known to be expressed more in HIV-1-infected T cells or macrophages. The results support the emerging model in which one of the roles of gp41 folding into the SHB conformation is to slow down membrane disruption effects induced by early exposed gp41. However, it can further affect membrane morphology once exposed to negatively charged membranes during late stages.

Measuring the mechanical properties of single-stranded DNA (ssDNA) is a challenge that has been addressed by different methods lately. The short persistence length, fragile structure, and the appearance of stem loops complicate the measurement, and this leads to a large variability in the measured values. Here we describe an innovative method based on DNA origami for studying the biophysical properties of ssDNA. By synthesizing a DNA origami structure that consists of two rigid rods with an ssDNA segment between them, we developed a method to characterize the effective persistence length of a random-sequence ssDNA while allowing the formation of stem loops. We imaged the structure with an atomic force microscope (AFM); the rigid rods provide a means for the exact identification of the ssDNA ends. This leads to an accurate determination of the end-to-end distance of each ssDNA segment, and by fitting the measured distribution to the ideal chain polymer model we measured an effective persistence length of 1.98 ± 0.72 nm. This method enables one to measure short or long strands of ssDNA, and it can cope with the formation of stem loops that are often formed along ssDNA. We envision that this method can be used for measuring stem loops for determining the effect of repetitive nucleotide sequences and environmental conditions on the mechanical properties of ssDNA and the effect of interacting proteins with ssDNA. We further noted that the method can be extended to nanoprobes for measuring the interactions of specific DNA sequences, because the DNA origami rods (or similar structures) can hold multiple fluorescent probes that can be easily detected.