Preparation and study of the physicochemical characteristics of multilayer polymer composites based on poly(ethyleneimine)-stabilized copper nanoparticles and poly(sodium 2-acrylamide-2-methyl-1-propanesulfonate)

Multilayer films were synthesized from a complex of branched polyethyleneimine (PEI) with copper nanoparticles (PEI-CuNPs) and sodium poly-2-acrylamide-2-methyl-1-propanesulfonate (PAMPSNa), applied layer-by-layer (LbL) on a solid support in an acidic medium. Protonation of the amino groups of PEI in an acidic medium increases the positive charge of the PEI-CuNPs system to +43.5 mV and promotes the formation of an interpolyelectrolyte complex between the positively charged PEI-CuNPs and the highly charged anionic polyelectrolyte PAMPS, the ζ-potential of which was -141 mV. AFM images and SEM micrographs showed a uniform distribution of spherical copper nanoparticles in the homogeneous structure of the multilayer film. The optical characteristics and hydrodynamic dimensions of PEI-CuNPs indicate the formation of PEI-CuNPs nanoparticles with sizes of 60-300 nm, with an average size of up to 100 nm. Copper nanoparticles distributed uniformly in a multilayer PEI-CuNPs/PAMPS film may be of interest for applications in the field of membrane catalysis, biochips, sensor membranes, and controlled drug delivery.

Identification of a conformational heparin-recognition motif on the peptide hormone secretin: key role for cell surface binding

Secretin is a peptide hormone that exerts pleiotropic physiological functions by specifically binding to its cognate membrane-bound receptor. The membrane catalysis model of peptide–receptor interactions states that soluble peptidic ligands initially interact with the plasma membrane. This interaction increases the local concentration and structures the peptide, enhancing the rate of receptor binding. However, this model does not consider the dense network of glycosaminoglycans (GAGs) at the surface of eukaryotic cells. These sulfated polysaccharide chains are known to sequester numerous proteic signaling molecules. In the present study, we evaluated the interaction between the peptide hormone secretin and sulfated GAGs and its contribution to cell surface binding. Using GAG-deficient cells and competition experiments with soluble GAGs, we observed by confocal microscopy and flow cytometry that GAGs mediate the sequestration of secretin at the cell surface. Isothermal titration calorimetry and surface plasmon resonance revealed that secretin binds to heparin with dissociation constants ranging between 0.9 and 4 μM. By designing secretin derivatives with a restricted conformational ensemble, we observed that this interaction is mediated by the presence of a specific conformational GAG-recognition motif that decorates the surface of the peptide upon helical folding. The present study identifies secretin as a novel GAG-binding polypeptide and opens new research direction on the functional role of GAGs in the biology of secretin.