Inhibition of antithrombin and bovine serum albumin native state aggregation by heparin

Achieving superior anticoagulation of endothelial membrane mimetic coating by heparin grafting at zwitterionic biocompatible interfaces

Thrombosis and bleeding are common complications of blood-contacting medical device therapies. In this work, an endothelium membrane mimetic coating (PMPCC/Hep) has been created to address these challenges. The coating is fabricated by multi-point anchoring of a phosphorylcholine copolymer (poly-MPC-co-MSA, PMPCC) with carboxylic side chains and end-group grafting of unfractionated heparin (Hep) onto polydopamine precoated blood-contacting material surfaces. The PMPCC coating forms an ultrathin cell outer membrane mimetic layer to resist protein adsorption and platelet adhesion. The tiny defects/pores of the PMPCC layer provide entrances for heparin end-group to be inserted and grafted onto the sub-layer amino groups. The combination of the PMPCC cell membrane mimetic anti-fouling nature with the grafted heparin bioactivity further enhances the anticoagulation performance of the formed endothelium membrane mimetic PMPCC/Hep coating. Compared to conventional Hep coating, the PMPCC/Hep coating further decreases protein adsorption and platelet adhesion by 50 % and 90 %, respectively. More significantly, the PMPCC/Hep coating shows a superior anticoagulation activity, even significantly higher than that of an end-point-attached heparin coating. Furthermore, the blood coagulation function is well preserved in the PMPCC/Hep coating anticoagulation strategy. All the results support that the PMPCC/Hep coating strategy has great potential in developing more efficient and safer blood-contacting medical devices.

Evaluation of properties and structural transitions of Poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) / β-Galactosidase complex coacervates: effects of pH and aging

The coacervates of the Poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) / β-Galactosidase complex are characterized using several techniques (Turbidimetry, dynamic and static light scattering (DLS / SLS), optical microscopy, image dynamic light scattering (IDLS), and ultra-small angles light scattering (USALS)). Turbidity and SLS were used to accurately determine the critical pHs of complex formation (pH_c, pH_ϕ1, pH_opt, and pH_ϕ2), DLS was used to probe the microscopic structure of coacervate droplets rich in proteins and polyelectrolytes in liquid-liquid phase separation, and IDLS and USALS have been introduced to better understand, during aging, the topology of the network formed of materials based on fractals in the dense phase. Observations of the architecture, the spatial inhomogeneity, and the size distributions of liquid complex coacervate droplets and fractal solid precipitates, were performed by optical microscopy. The pair-distance distribution function, P(r), presented in this review, is a new methodology of calculus for determining with precision the radius of gyration R_g of droplets coacervates. These techniques show that aging improves the stability of swollen condensates, the growth of the coacervate droplets is due to the attractive electrostatic interactions within the complex and does not undergo Ostwald ripening, except for the case of pH_opt and having fractal dimensions D_f generated by diffusion-limited cluster aggregation (DLCA).

Fluorescence enables high throughput screening of polyelectrolyte–protein binding affinities

Förster resonance energy transfer (FRET) in combination with high throughput controlled radical polymerisation allows quick identification of polymers that can bind strongly to enzymes such as glucose oxidase.

Understanding the Interaction of Polyelectrolyte Architectures with Proteins and Biosystems

The counterions neutralizing the charges on polyelectrolytes such as DNA or heparin may dissociate in water and greatly influence the interaction of such polyelectrolytes with biomolecules, particularly proteins. In this Review we give an overview of studies on the interaction of proteins with polyelectrolytes and how this knowledge can be used for medical applications. Counterion release was identified as the main driving force for the binding of proteins to polyelectrolytes: Patches of positive charge become multivalent counterions of the polyelectrolyte and lead to the release of counterions from the polyelectrolyte and a concomitant increase in entropy. This is shown from investigations on the interaction of proteins with natural and synthetic polyelectrolytes. Special emphasis is paid to sulfated dendritic polyglycerols (dPGS). The Review demonstrates that we are moving to a better understanding of charge-charge interactions in systems of biological relevance. Research along these lines will aid and promote the design of synthetic polyelectrolytes for medical applications.

Protein-Polyelectrolyte Complexes and Micellar Assemblies

In this review, we highlight the recent progress in our understanding of the structure, properties and applications of protein-polyelectrolyte complexes in both bulk and micellar assemblies. Protein-polyelectrolyte complexes form the basis of the genetic code, enable facile protein purification, and have emerged as enterprising candidates for simulating protocellular environments and as efficient enzymatic bioreactors. Such complexes undergo self-assembly in bulk due to a combined influence of electrostatic interactions and entropy gains from counterion release. Diversifying the self-assembly by incorporation of block polyelectrolytes has further enabled fabrication of protein-polyelectrolyte complex micelles that are multifunctional carriers for therapeutic targeted delivery of proteins such as enzymes and antibodies. We discuss research efforts focused on the structure, properties and applications of protein-polyelectrolyte complexes in both bulk and micellar assemblies, along with the influences of amphoteric nature of proteins accompanying patchy distribution of charges leading to unique phenomena including multiple complexation windows and complexation on the wrong side of the isoelectric point.

Study of the complex coacervation mechanism between the lysing enzyme from T. harzianum and polyallylamine hydrochloride

Complex coacervation was achieved by mixing the lysing enzyme from T. harzianum (LYS) with polyallylamine hydrochloride (PAH). We show in this work that the study electrostatic complexes conformation can lead to the formation of dense complexes. We systematically investigated the effects of pH and the mass ratio on the structure and properties of the complex. The different transition phases (pHc, pHφ1, and pHφ2) have been determined using dynamic light scattering, zeta potential and turbidimetric measurements. The interpolymeric bonds may be ionic or physical, depending on the pH of the system. For a pH value of 4.9, the mixture system [LYS]/[PAH] gives raise the formation of coacervate droplets. The effects of temperature on the structure of coacervate droplets are studied by small angle light scattering (SALS).

Sugar-Terminated Nanoparticle Chaperones Are 102-105 Times Better Than Molecular Sugars in Inhibiting Protein Aggregation and Reducing Amyloidogenic Cytotoxicity

Sugar-based osmolyte molecules are known to stabilize proteins under stress, but usually they have poor chaperone performance in inhibiting protein aggregation. Here, we show that the nanoparticle form of sugars molecule can enhance their chaperone performance typically by 10²-10⁵ times, compared to molecular sugar. Sugar-based plate-like nanoparticles of 20-40 nm hydrodynamic size have been synthesized by simple heating of acidic aqueous solution of glucose/sucrose/maltose/trehalose. These nanoparticles have excitation-dependent green/yellow/orange emission and surface chemistry identical to the respective sugar molecule. Fibrillation of lysozyme/insulin/amyloid beta in extracellular space, aggregation of mutant huntingtin protein inside model neuronal cell, and cytotoxic effect of fibrils are investigated in the presence of these sugar nanoparticles. We found that sugar nanoparticles are 10²-10⁵ times efficient than respective sugar molecules in inhibiting protein fibrillation and preventing cytotoxicity arising of fibrils. We propose that better performance of the nanoparticle form is linked to its stronger binding with fibril structure and enhanced cell uptake. This result suggests that nanoparticle form of osmolyte can be an attractive option in prevention and curing of protein aggregation-derived diseases.

Resonance Rayleigh scattering detection of heparin with concanavalin A

Stepwise macromolecular interactions observed between conA and heparin, which are accompanied by RRS changes.

Prevention of aggregation and renaturation of carbonic anhydrase via weak association with octadecyl- or azobenzene-modified poly(acrylate) derivatives

The prevention of aggregation during renaturation of urea-denatured carbonic anhydrase B (CAB) via hydrophobic and Coulomb association with anionic polymers was studied in mixed solutions of CAB and amphiphilic poly(acrylate) copolymers. The polymers were derivatives of a parent poly(acrylic acid) randomly grafted with hydrophobic side groups (either 3 mol % octadecyl group, or 1-5 mol % alkylamidoazobenzene photoresponsive groups). CAB:polymer complexes were characterized by light scattering and fluorescence correlation spectroscopy in aqueous buffers (pH 7.75 or 5.9). Circular dichroism and enzyme activity assays enabled us to study the kinetics of renaturation. All copolymers, including the hydrophilic PAA parent chain, provided a remarkable protective effect against CAB aggregation during renaturation, and most of them (but not the octadecyl-modified one) markedly enhanced the regain of activity as compared to CAB alone. The significant role of Coulomb binding in renaturation and comparatively the lack of efficacy of hydrophobic association was highlighted by measurements of activity regain before and after in situ dissociation of hydrophobic complexes (achieved by phototriggering the polarity of azobenzene-modified polymers under exposure to UV light). In the presence of polymers (CAB:polymer of 1:1 w/w ratio) at concentration ∼0.6 g L(-1), the radii of the largest complexes were similar to the radii of the copolymers alone, suggesting that the binding of CAB involves one or a few polymer chain(s). These complexes dissociated by dilution (0.01 g L(-1)). It is concluded that prevention of irreversible aggregation and activity recovery were achieved when marginally stable complexes are formed. Reaching a balanced stability of the complex plays the main role in CAB renaturation, irrespective of the nature of the binding (by Coulomb association, with or without contribution of hydrophobic association).