Effect of Surface Hydrophobicity on the Adsorption of a Pilus-Derived Adhesin-like Peptide.

Bacterial colonization of abiotic surfaces such as those of medical implants, membrane filters, and everyday household items is a process of tremendous importance for public health. Bacteria use adhesive cell surface structures called adhesins to establish contact with abiotic surfaces. Among them, protein filaments called type IV pili are particularly important and found in many Gram-negative pathogens such as Pseudomonas aeruginosa. Understanding the interaction of such adhesin proteins with different abiotic surfaces at the molecular level thus represents a fundamental prerequisite for impeding bacterial colonization and preventing the spread of infectious diseases. In this work, we investigate the interaction of a synthetic adhesin-like peptide, PAK128-144ox, derived from the type IV pilus of P. aeruginosa with hydrophilic and hydrophobic self-assembled monolayers (SAMs). Using a combination of molecular dynamics (MD) simulations, quartz crystal microbalance with dissipation monitoring (QCM-D), and spectroscopic investigations, we find that PAK128-144ox has a higher affinity for hydrophobic than for hydrophilic surfaces. Additionally, PAK128-144ox adsorption on the hydrophobic SAM is furthermore accompanied by a strong increase in α-helix content. Our results show a clear influence of surface hydrophobicity and further indicate that PAK128-144ox adsorption on the hydrophobic surface is enthalpically favored, while on the hydrophilic surface, entropic contributions are more significant. However, our spectroscopic investigations also suggest aggregation of the peptide under the employed experimental conditions, which is not considered in the MD simulations and should be addressed in more detail in future studies.

Cold denaturation of DNA origami nanostructures.

The coupling of structural transitions to heat capacity changes leads to destabilization of macromolecules at both elevated and lowered temperatures. DNA origami not only exhibit this property but also provide a nanoscopic observable of cold denaturation processes by directing intramolecular strain to the most sensitive elements within their hierarchical architecture.

Superstructure-dependent stability of DNA origami nanostructures in the presence of chaotropic denaturants.

The structural stability of DNA origami nanostructures in various chemical environments is an important factor in numerous applications, ranging from biomedicine and biophysics to analytical chemistry and materials synthesis. In this work, the stability of six different 2D and 3D DNA origami nanostructures is assessed in the presence of three different chaotropic salts, i.e., guanidinium sulfate (Gdm2SO4), guanidinium chloride (GdmCl), and tetrapropylammonium chloride (TPACl), which are widely employed denaturants. Using atomic force microscopy (AFM) to quantify nanostructural integrity, Gdm2SO4 is found to be the weakest and TPACl the strongest DNA origami denaturant, respectively. Despite different mechanisms of actions of the selected salts, DNA origami stability in each environment is observed to depend on DNA origami superstructure. This is especially pronounced for 3D DNA origami nanostructures, where mechanically more flexible designs show higher stability in both GdmCl and TPACl than more rigid ones. This is particularly remarkable as this general dependence has previously been observed under Mg2+-free conditions and may provide the possibility to optimize DNA origami design toward maximum stability in diverse chemical environments. Finally, it is demonstrated that melting temperature measurements may overestimate the stability of certain DNA origami nanostructures in certain chemical environments, so that such investigations should always be complemented by microscopic assessments of nanostructure integrity.

Anion-specific structure and stability of guanidinium-bound DNA origami.

While the folding of DNA into rationally designed DNA origami nanostructures has been studied extensively with the aim of increasing structural diversity and introducing functionality, the fundamental physical and chemical properties of these nanostructures remain largely elusive. Here, we investigate the correlation between atomistic, molecular, nanoscopic, and thermodynamic properties of DNA origami triangles. Using guanidinium (Gdm) as a DNA-stabilizing but potentially also denaturing cation, we explore the dependence of DNA origami stability on the identity of the accompanying anions. The statistical analyses of atomic force microscopy (AFM) images and circular dichroism (CD) spectra reveals that sulfate and chloride exert stabilizing and destabilizing effects, respectively, already below the global melting temperature of the DNA origami triangles. We identify structural transitions during thermal denaturation and show that heat capacity changes ΔC p determine the temperature sensitivity of structural damage. The different hydration shells of the anions and their potential to form Gdm+ ion pairs in concentrated salt solutions modulate ΔC p by altered wetting properties of hydrophobic DNA surface regions as shown by molecular dynamics simulations. The underlying structural changes on the molecular scale become amplified by the large number of structurally coupled DNA segments and thereby find nanoscopic correlations in AFM images.

How do U.S. medical oncologists learn and apply new clinical trials information from press releases in nonmedical media? A case study based on ECOG 4599.

BACKGROUND: Practicing oncologists are expected to easily assimilate large amounts of rapidly evolving clinical data. We hypothesized that U.S. oncologists rapidly familiarize themselves with new, practice-relevant, phase III clinical trial data. We tested this hypothesis in relation to the release of phase III data from the Eastern Cooperative Oncology Group 4599 trial on the role of bevacizumab in advanced non-small cell lung cancer (NSCLC). METHODS: We queried approximately 310 medical oncologists concerning their awareness of the bevacizumab data within 1 and 3 weeks after the data release or immediately after the 2005 Annual Meeting of the American Society of Clinical Oncology (ASCO). RESULTS: Prior to the ASCO meeting, 57% and 56% of the oncologists in the two research meetings, respectively, indicated "awareness" of the data release. Less than 25% selected an accurate descriptor of the released information from a short list of plausible options. After the ASCO meeting, the figures were 88% and 34%. Over 50% said they plan to use bevacizumab in NSCLC treatment as soon as reimbursement is secure. Eighty-two percent said they plan to use it in second- or third-line treatment; 56% said they plan to use it during second-line chemotherapy despite progression during first-line use. A large majority intend to use bevacizumab in dosages, tumor types, drug combinations, and/or patients not specifically supported by phase III data. CONCLUSION: Release of clinically relevant phase III data through electronic and print media is a poor vehicle for informing U.S. medical oncologists. For a commercially available agent, this can have important implications for potential use in untested and potentially unsafe clinical settings. Effective educational strategies for dealing with the new paradigm of "instant" release of clinical data need to be developed.