Polymer intrusion into narrow pores at the interface between a poor solvent and adsorbing and non-adsorbing surfaces

We report thermodynamic and conformational properties of collapsed polymer globules in a poor solvent close to adsorbing and non-adsorbing surfaces containing a cylindrical pore that is either smaller or larger than the coil size in bulk solution. Configurational Bias Monte Carlo simulations at infinite dilution were used for this purpose. We find that above the critical adsorption transition changing from good solvent to poor solvent conditions causes an increase of the partition coefficient due to cooperative monomer adsorption on the pore wall. Below the adsorption transition, the reverse effect is observed. The radius of gyration components as well as conformational (free) energies and entropies as a function of the chain centre of mass (CM) position along the pore axis reveal strong anomalies in the vicinity of the pore entrance. Below the adsorption transition, the dense globule in a poor solvent swells and deforms when penetrating the pore and recollapses once it is fully confined. Above the adsorption transition in solvents above and below the Θ-point, minima occur in the free energy at chain CM positions just in front of the pore entry causing a barrier upon pore penetration. Upon approaching the small pore from the bulk poor solvent region, the chain conformational entropy and energy run through a maximum below and above the adsorption transition.\u

Evolution of recognition of ligands from gram-positive bacteria: similarities and differences in the TLR2-mediated response between mammalian vertebrates and teleost fish

We investigated the role of the TLR2 receptor in the recognition of ligands from Gram-positive bacteria in fish. Comparative sequence analysis showed a highly conserved Toll/IL-1 receptor domain. Although the leucine-rich repeat domain was less conserved, the position of the critical peptidoglycan (PGN)-binding residues in the leucine-rich repeat domain of carp TLR2 were conserved. Transfection of human embryonic kidney 293 cells with TLR2 corroborated the ability of carp TLR2 to bind the prototypical mammalian vertebrate TLR2 ligands lipoteichoic acid (LTA) and PGN from Staphylococcus aureus. The synthethic triacylated lipopeptide N-palmitoyl-S-(2,3-bis(palmitoyloxy)-(2RS)-propyl)-(R)-Cys-(S)-Ser-(S)-Lys4 trihydrochloride (Pam3CSK4) but not the diacylated lipopeptide macrophage-activating lipopeptide-2 (MALP-2) also activated TLR2 transfected human cells. We identified clear differences between the mammalian vertebrates and carp TLR2-mediated response. The use of the same ligands on carp macrophages indicated that fish cells require high concentrations of ligands from Gram-positive bacteria (LTA, PGN) for activation and signal transduction, react less strongly (Pam3CSK4) or do not react at all (MALP-2). Overexpression of TLR2 in carp macrophages confirmed TLR2 reactivity of the response to LTA and PGN, low-responsiveness to Pam3CSK4 and nonresponsiveness to MALP-2. A putative relation with the apparent absence of accessory proteins such as CD14 from the fish TLR2-containing receptor complex is discussed. Moreover, activation of carp macrophages by PGN resulted in increased TLR2 gene expression and enhanced TLR2 mRNA stability, MAPK-p38 phosphorylation and increased radical production. Finally, we could show that NADPH oxidase-derived radicals and MAPK-p38 activation cooperatively determine the level of PGN-induced TLR2 gene expression. We propose that the H2O2-MAPK-p38–dependent axis is crucial for regulation of TLR2 gene expression in fish macrophages

Monte Carlo Simulation of Partially Confined Flexible Polymers

We have studied conformational properties of flexible polymers partially confined to narrow pores of different size using configurational biased Monte Carlo simulations under athermal conditions. The asphericity of the chain has been studied as a function of its center of mass position along the pore axis and as a function of the degree of penetration, or fraction of confined segments. The asphericity passes through a maximum well before all segments are located inside the pore. Rather than deforming gradually, we find that at intermediate penetration degrees, where the center of mass is within distances of approximately one radius of gyration away from the pore entry, the chain part inside the pore stretches out considerably while the remaining part outside the pore is coillike ("flower conformations"). When the center of mass is located further inside the pore, this strong chain extension along the pore axis diminishes, and the average conformation becomes that of a deformed coil. Introduction of weakly attractive monomer-wall interactions does not affect these observations significantly