pH-response of protein-polysaccharide multilayers adsorbed on a flat gold surface: A surface plasmon resonance study.

Polysaccharide-protein multilayers (PPMLs) consisting of bovine serum albumin (BSA) and chondroitin sulfate (CS) are assembled in acidic solution (pH 4.2) via layer-by-layer deposition method. The formation of PPMLs on gold surface and their responsiveness to pH change from 4.2 to 7 is investigated by Surface Plasmon Resonance Spectroscopy. The buildup of the multilayer at pH 4.2 exhibits non-linear growth while the formation of the first layers is strongly affected by the physicochemical properties of the gold surface. Neutral solution (pH 7) affects the interactions between the biopolymers and results in a partially disassemble (disintegration) of the multilayer film. On one hand, the single pair of layers, BSA-CS and the double pair of layers, (BSA-CS)2, assemblies are stable in neutral pH, a result that will be of interest for biomedical applications. On the other hand, multilayer films consisting of more than four layers that is (BSA-CS)2

Complexation of lysozyme with adsorbed PtBS-b-SCPI block polyelectrolyte micelles on silver surface.

We present a study of the interaction of the positively charged model protein lysozyme with the negatively charged amphiphilic diblock polyelectrolyte micelles of poly(tert-butylstyrene-b-sodium (sulfamate/carboxylate)isoprene) (PtBS-b-SCPI) on the silver/water interface. The adsorption kinetics are monitored by surface plasmon resonance, and the surface morphology is probed by atomic force microscopy. The micellar adsorption is described by stretched-exponential kinetics, and the micellar layer morphology shows that the micelles do not lose their integrity upon adsorption. The complexation of lysozyme with the adsorbed micellar layers depends on the micelles arrangement and density in the underlying layer, and lysozyme follows the local morphology of the underlying roughness. When the micellar adsorbed amount is small, the layers show low capacity in protein complexation and low resistance in loading. When the micellar adsorbed amount is high, the situation is reversed. The adsorbed layers both with or without added protein are found to be irreversibly adsorbed on the Ag surface.

Thermally stabilized chondroitin sulfate-hemoglobin nanoparticles and their interaction with bioactive compounds.

The preparation of nanoparticles (NPs) based on hemoglobin (Hb) with a fully biocompatible methodology is presented. The spontaneous formation of electrostatic complexes of Hb with chondroitin sulfate (CS) at pH 4 in the polysaccharide/protein mass ratio regime where charge neutrality is met leads to spherical nanostructures with monomodal hydrodynamic radii distribution in the range of 50-100 nm. The integrity of the electrostatic complexes is disturbed at pH 7 as the net electric charge of Hb is very low. Treating the NPs at mildly elevated temperature stabilizes them against the pH increase taking advantage of Hb's ability of unfolding and self-associating upon thermal treatment. The NPs surface charge is pH-tunable and changes from positive to strongly negative upon pH increase to 7 proving the presence of negative surface patches of Hb and CS segments in their exterior. The α-helix content of Hb does not change significantly by thermal treatment. The NPs are found to bind the bioactive compounds curcumin and ß-carotene and are stable in solutions with high salt content. This investigation introduces a straightforward method to formulate Hb in NPs with possibilities in the nanodelivery of nutrients and drugs.

A peptide corresponding to the C-terminal region of pleiotrophin inhibits angiogenesis in vivo and in vitro.

Pleiotrophin (PTN) is a heparin-binding growth factor that plays a significant role in tumor growth and angiogenesis. We have previously shown that in order for PTN to induce migration of endothelial cells, binding to both α(ν) ß(3) integrin and its receptor protein tyrosine phosphatase beta/zeta (RPTPß/ζ) is required. In the present study we show that a synthetic peptide corresponding to the last 25 amino acids of the C-terminal region of PTN (PTN(112-136) ) inhibited angiogenesis in the in vivo chicken embryo chorioallantoic membrane (CAM) assay and PTN-induced migration and tube formation of human endothelial cells in vitro. PTN(112-136) inhibited binding of PTN to α(ν) ß(3) integrin, and as shown by surface plasmon resonance (SPR) measurements, specifically interacted with the specificity loop of the extracellular domain of ß(3) . Moreover, it abolished PTN-induced FAK Y397 phosphorylation, similarly to the effect of a neutralizing α(ν) ß(3) -selective antibody. PTN(112-136) did not affect binding of PTN to RPTPß/ζ in endothelial cells and induced ß(3) Y773 phosphorylation and ERK1/2 activation to a similar extent with PTN. This effect was inhibited by down-regulation of RPTPß/ζ by siRNA or by c-src inhibition, suggesting that PTN(112-136) may interact with RPTPß/ζ. NMR spectroscopy studies showed that PTN(112-136) was characterized by conformational flexibility and absence of any element of secondary structure at room temperature, although the biologically active peptide segment 123-132 may adopt a defined structure at lower temperature. Collectively, our data suggest that although PTN(112-136) induces some of the signaling pathways triggered by PTN, it inhibits PTN-induced angiogenic activities through inhibition of PTN binding to α(ν) ß(3) integrin.

Formation of polymer brushes inside cylindrical pores: a computer simulation study.

The formation process of polymer brushes, formed by the adsorption of flexible end-functionalized chains from dilute solutions on the inner surface of cylindrical pores is studied by bond fluctuation Monte Carlo simulations. Various properties as the grafting density, monomer, and free-end distribution are monitored as a function of pore diameter D and chain length N. Two different modes of end-segment attachment on the inner pore surface are considered: (a) pure-irreversible "hard" grafting and (b) irreversible "soft" grafting where grafted-ends can move freely on the pore surface but cannot detach from it. Different regimes of pore coating are identified, depending on the mode of end-segment attachment and on the ratio of D to the radius of gyration of the free polymer chains in solution R(g). These initial findings can be used as a guide for the preparation of actual polymer brushes inside ordered porous membranes by the "grafting to" approach.