Complex protein-polyelectrolyte

The formation of salt bridges in polyelectrolyte/protein complexes is widely accepted. Direct evidences for the release of counterions upon association of the macromolecular partners are however scarcely reported. Potentio-metric studies were found to reveal the ionization or neutralization of proteins in polymer complexes, i.e., a pKa shift of ionizable residues when an association took place [23,25,30], In the presence of neutral polyethylene glycol, pepsin was shown to take up protons from the solution [30], On the contrary, bovine serum albumin released protons from the addition of poly(diallyldimethylammonium chloride) (Figure 5). Despite the simplicity of both the method and the quantitative measurement of a number of ions released per protein, an interpretation in terms of a number of local bridges... 

In [93-95] a combination of turbidimetry and static and dynamic light scattering was applied to study the structure of complexes between PDADMAC samples of different molecular weights and charged mixed micelles. A review on such studies of polyelectrolyte-protein complexes is given in [96]. 

Cooper CL, Dubin PL, Kayitmazer AB et al (2005) Polyelectrolyte-protein complexes. Curr Opin Colloid Interface Sci 10 52-78... 

Gummel J, Boue F, Deme B et al (2006) Charge stoichiometry inside polyelectrolyte-protein complexes a direct SANS measurement for the PSSNa-lysozyme system. J Phys Chem B 110 24837-24846... 

We hope that the topics discussed in this chapter will help readers to understand the properties of solutions of charged polymers and will be useful in future studies of more complicated ionic systems, such as polyelectrolyte gels, polyelectrolyte bmshes, ° polyelectrolyte-protein complexes, ionomers, charged polymers at surfaces and interfaces, and multilayer formation by charged molecules. ... 

A.B. andTurksen, S. (2005) Polyelectrolyte-protein complexes. Current Opinion in Colloid and Interface Science,... 

Cooper, C.L., et al. Polyelectrolyte-protein complexes. Curr. Opin. Colloid Interface Sci. 10(1-2), 52-78 (2005)... 

Carlsson, F., Linse, P., Malmsten, M. Monte Carlo simulations of polyelectrolyte-protein complexation. J. Phys. Chem. B 105(38), 9040-9049 (2001)... 

From the physics point of view, the system that we deal with here—a semiflexible polyelectrolyte that is packaged by protein complexes regularly spaced along its contour—is of a complexity that still allows the application of analytical and numerical models. For quantitative prediction of chromatin properties from such models, certain physical parameters must be known such as the dimensions of the nucleosomes and DNA, their surface charge, interactions, and mechanical flexibility. Current structural research on chromatin, oligonucleosomes, and DNA has brought us into a position where many such elementary physical parameters are known. Thus, our understanding of the components of the chromatin fiber is now at a level where predictions of physical properties of the fiber are possible and can be experimentally tested. 

Specific interactions between starch and proteins were observed as early as the beginning of the twentieth century. Berczeller996 noted that the surface tension of aqueous soap solutions did not decrease with the addition of protein (egg albumin) alone, but it did decrease when starch and protein were added. This effect was observed to increase with time. Sorption of albumin on starch is inhibited by bi- and trivalent ions and at the isoelectric point. Below the isoelectric point, bonding between starch and albumin is ionic in character, whereas nonionic interactions are expected above the isoelectric point.997 The Terayama hypothesis998 predicts the formation of protein complexes with starch, provided that starch exhibits the properties of a polyelectrolyte. Apart from chemically modified anionic starches (such as starch sulfate, starch phosphate, and various cross-linked starch derivatives bearing ionized functions), potato starch is the only variety that behaves as a polyelectrolyte. Its random phosphate ester moieties permit proteins to form complexes with it. Takeuchi et a/.999-1002 demonstrated such a possibility with various proteins and a 4% gel of potato starch. 

One example of a practical application where polyelectrolytes are of crucial interest are immunoassays, where charged polymers are attached to surfaces and are then exposed to protein solution with the aim of loading of the polymer layer with a reproducible amount of these proteins. The protein-loaded particles or planar films thus obtained are in turn exposed to analyte solutions containing other proteins. If the proteins in the film match the proteins in solution, protein-protein complexes are formed, which are then visualized and/or quantified. In order to complete such a process successfully knowledge about the swelling of the polyelectrolyte layer in buffer solutions and the interaction of such a layer with proteins has to be established. Further questions, which are of great importance for such polyelectrolyte systems are the behavior of the monolayers in contact with common impurities present in contacting solutions especially traces of multivalent ions or tensides. 

Polyelectrolytes Binding to the protein may increase solubility high molecular weight protein complexes may also form which could decrease solubility Increased charge density or conformational change Potential pharmacological effect or toxicity of the excipients... 

Morawetz H., Hugues W. L. The interaction of proteins with synthetic polyelectrolytes. I. Complexing of bovine serum albumin. J. Phys. Chem 1951 56 64-69. 

Over the years, the theory of polyelectrolyte complex formation has been further developed. The theory of Voom and Overbeek was later extended by Nakajima and Sato, who included an interaction parameter x to account for additional interactions such as hydrophobicity [16]. Correlation effects within the dense complex phase were included in the theory by Castelnovo and Joanny, which enables prediction of a critical salt concentration [17]. Kramarenko and Khokhlov included specific ionpairing energies, but their theory ignores the formation of ion pairs between polyelectrolytes and monovalent counterions hence, they do not present a salt dependence of the complex formation [18]. Heterogenous cell models can be used to describe experimental data on polyelectrolyte complex formation. These models take the spatial structure of the complex into account [19]. In Sect. 3 on protein-protein complexation we discuss how such a model can be used to describe experimental data. 

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