The dependence of the optical properties of spherical gold nanoparticles on particle size and wavelength were analyzed theoretically using multipole scattering theory, where the complex refractive index of gold was corrected for the effect of a reduced mean free path of the conduction electrons in small particles. To compare these theoretical results to experimental data, gold nanoparticles in the size range of 5 to 100 nm were synthesized and characterized with TEM and UV-vis. Excellent agreement was found between theory and experiment. It is shown that the data produced here can be used to determine both size and concentration of gold nanoparticles directly from UV-vis spectra. Equations for this purpose are derived, and the precision of various methods is discussed. The major aim of this work is to provide a simple and fast method to determine size and concentration of nanoparticles.

Based on protein folding considerations, a pentapeptide ligand, CALNN, which converts citrate-stabilized gold nanoparticles into extremely stable, water-soluble gold nanoparticles with some chemical properties analogous to those of proteins, has been designed. These peptide-capped gold nanoparticles can be freeze-dried and stored as powders that can be subsequently redissolved to yield stable aqueous dispersions. Filtration, size-exclusion chromatography, ion-exchange chromatography, electrophoresis, and centrifugation can be applied to these particles. The effect of 58 different peptide sequences on the electrolyte-induced aggregation of the nanoparticles was studied. The stabilities conferred by these peptide ligands depended on their length, hydrophobicity, and charge and in some cases resulted in further improved stability compared with CALNN, yielding detailed design criteria for peptide capping ligands. A simple strategy for the introduction of recognition groups is proposed and demonstrated with biotin and Strep-tag II.

We present a generalized table of extinction coefficient data for silver nanoparticles from 8 to 100 nm. This table allows for easy and quick estimation of the concentration and size of modified and mono-dispersed silver nanoparticles from their optical spectra. We obtained data by determining the silver content of citrate-stabilised silver nanoparticles using sodium cyanide to dissolve the nanoparticles, and measuring solution conductivity with a pH meter and a cyanide-ion selective electrode. The quantification of the silver ion concentration enabled the calculation of extinction coefficients. Experimentally calculated extinction coefficients, in the current work, are in good agreement with collated literature values measured by different authors with non-standardized methodology and each for a limited range of particle size. They are also in good agreement with our theoretical calculations using Mie theory. Thus, we provide a highly standardized and comprehensive tabulated reference data-set.

A large body of evidence supports the involvement of heparan sulfate (HS) proteoglycans in physiological processes such as development and diseases including cancer and neurodegenerative disorders. The role of HS emerges from its ability to interact and regulate the activity of a vast number of extracellular proteins including growth factors and extracellular matrix components. A global view on how protein-HS interactions influence the extracellular proteome and, consequently, cell function is currently lacking. Here, we systematically investigate the functional and structural properties that characterize HS-interacting proteins and the network they form. We collected 435 human proteins interacting with HS or the structurally related heparin by integrating literature-derived and affinity proteomics data. We used this data set to identify the topological features that distinguish the heparin/HS-interacting network from the rest of the extracellular proteome and to analyze the enrichment of gene ontology terms, pathways, and domain families in heparin/HS-binding proteins. Our analysis revealed that heparin/ HS-binding proteins form a highly interconnected network, which is functionally linked to physiological and pathological processes that are characteristic of higher organisms. Therefore, we then investigated the existence of a correlation between the expansion of domain families characteristic of the heparin/HS interactome and the increase in biological complexity in the metazoan lineage. A strong positive correlation between the expansion of the heparin/HS interactome and biosynthetic machinery and organism complexity emerged. The evolutionary role of HS was reinforced by the presence of a rudimentary HS biosynthetic machinery in a unicellular organism at the root of the metazoan lineage.

Many pathogens take advantage of the dependence of the host on the interaction of hundreds of extracellular proteins with the glycosaminoglycans heparan sulfate to regulate homeostasis and use heparan sulfate as a means to adhere and gain access to cells. Moreover, mucosal epithelia such as that of the respiratory tract are protected by a layer of mucin polysaccharides, which are usually sulfated. Consequently, the polydisperse, natural products of heparan sulfate and the allied polysaccharide, heparin have been found to be involved and prevent infection by a range of viruses including S-associated coronavirus strain HSR1. Here we use surface plasmon resonance and circular dichroism to measure the interaction between the SARS-CoV-2 Spike S1 protein receptor binding domain (SARS-CoV-2 S1 RBD) and heparin. The data demonstrate an interaction between the recombinant surface receptor binding domain and the polysaccharide. This has implications for the rapid development of a first-line therapeutic by repurposing heparin and for next-generation, tailor-made, GAG-based antivirals.

Over the past decade, the glycosaminoglycans heparin and heparan sulfate have been shown to bind and regulate the activities of many proteins. Established techniques have provided both qualitative and quantitative information regarding these interactions, leading to a general view that proteins bind with a variety of affinities to particular sequences within heparin or heparan sulfate chains. The mechanism by which heparan sulfate regulates the activity of proteins through such interactions has, however, proved more elusive. We survey some relevant details of the structural characteristics of heparin/heparan sulfate and the approaches used to investigate their interactions with proteins. For the latter, the interactions of heparin/heparan sulfate with fibroblast growth factors and their receptors will be emphasized, because these proteins have been the subject of many studies. We reflect on the information that various techniques have provided, points regarding their use, and some relevant theoretical considerations regarding the study of protein-heparin/heparan sulfate interactions. A perspective of new and developing approaches, which may aid advances in this field, is also provided.

Peptide-stabilized gold nanoparticles have been enzymatically biotinylated by a kinase-catalyzed reaction using biotin-ATP as a cosubstrate. Upon mixing with avidin-modified particles, solutions of biotinylated particles change color from red to blue, indicating aggregation of particles. On the basis of this reaction, we have developed a simple colorimetric test to monitor kinase inhibitor activity.

We have demonstrated by affinity chromatography that hepatocyte growth factor/scatter factor (HGF/SF) binds strongly to dermatan sulfate (DS), with a similar ionic strength dependence to that previously seen with heparan sulfate (HS). Analysis of binding kinetics on a biosensor yields an equilibrium dissociation constant, K D , of 19.7 nM. This corresponds to a 10 -100-fold weaker interaction than that with HS, primarily due to a faster dissociation rate of the complex. The smallest DS oligosaccharide with significant affinity for HGF/SF by affinity chromatography appears to be an octasaccharide. A sequence comprising unsulfated iduronate residues in combination with 4-O-sulfated N-acetylgalactosamine is sufficient for high affinity binding. The presence of 2-Osulfation on the iduronate residues does not appear to be inhibitory. These observations concur with our previous suggestions, from analyses of HS binding (Lyon, M., Deakin, J. A., Mizuno, K., Nakamura, T., and Gallagher, J.T. (1994) J. Biol. Chem. 269, 11216 -11223), that N-sulfation of hexosamines and 2-O-sulfation of iduronates are not absolute requirements for glycosaminoglycan binding to HGF/SF. This is the first described example of a high affinity interaction between a growth factor and DS, and is likely to have significant implications for the biological activity of this paracrine-acting factor.Hepatocyte growth factor/scatter factor (HGF/SF) 1 is a pleiotropic factor with the ability to influence the growth, motility, differentiation, and morphogenesis of its target cells (for a recent review, see Ref. 1). It acts in a paracrine manner, with the major secretors being fibroblasts, vascular smooth muscle cells, nonparenchymal liver cells, etc., whereas those cells that possess the requisite tyrosine kinase receptor (Met) are primarily epithelial and endothelial cells. Recent evidence suggests that multipotent and erythroid hemopoietic progenitor cells are also responsive to HGF/SF. The HGF/SF-Met system appears to operate primarily during the morphogenetic and differentiation events occurring in organogenesis, as well as in the repair of organ damage in the adult (reviewed in Ref. 1). Aberrant expression of HGF/SF and/or Met has been strongly implicated in tumor progression, particularly in the acquisition of an invasive malignant phenotype (2-5). This presumably results from its ability to directly stimulate the growth and motility of tumor cells, as well as increasing the secretion of matrix-degrading proteases (6), thereby facilitating invasion of the surrounding stroma. Additionally, its potent angiogenic action (7, 8) may contribute to the development of a tumor vasculature, which is essential for sustaining an expanding tumor mass.In addition to Met, HGF/SF also interacts in vitro with the heparan sulfate (HS) chains of heparan sulfate proteoglycans (HSPGs) (9). The latter probably constitute the more abundant, but relatively lower affinity, HGF/SF-binding sites present on most cells (10). The interaction of HGF/SF with cell surface HSPGs may ...