Polyanion-protein interactions

As polyanionic saccharides, heparinoids interact with a high number of proteins, the so-called heparin binding proteins. Heparinoid - protein interactions have usually been described for in vitro systems, and their physiological relevance is not always clear. On the other hand, heparinoids can influence biological systems, but in most cases the molecular basis is not fully understood. For this reason, interactions with proteins and biological properties of heparinoids will be discussed separately in the following. As heparinoid - protein interactions have been reviewed [3] the focus will be in rather short form on those areas in which heparinoid mimetics have been investigated. 

Fig. 3 Polyanionic dendrimers interacting with histone proteins, (a) Molecular structure of the first generation polyanionic dendrimer. (b) Confocal scanning niit scope images shown the co-localization of poly anionic dendrimer (5, red) with histone H4 proteins (green), (c) Isothermal titratimi graph shows the strong interaction between histone HI with 5. (d) Spectral analysis of the 5/histones...

High sorption capacities with respect to protein macromolecules are observed when highly permeable macro- and heteroreticular polyelectrolytes (biosorbents) are used. In buffer solutions a typical picture of interaction between ions with opposite charges fixed on CP and counterions in solution is observed. As shown in Fig. 13, in the acid range proteins are not bonded by carboxylic CP because the ionization of their ionogenic groups is suppressed. The amount of bound protein decreases at high pH values of the solution because dipolar ions proteins are transformed into polyanions and electrostatic repulsion is operative. The sorption maximum is either near the isoelectric point of the protein or depends on the ratio of the pi of the protein to the pKa=0 5 of the carboxylic polyelectrolyte [63]. It should be noted that this picture may be profoundly affected by the mechanism of interaction between CP and dipolar ions similar to that describedby Eq. (3.7). 

Being a polyanion, PolyP can interact with many proteins and enzymes, especially those rich in cationic amino acid residues. For example, in the presence of PolyP, cytochrome C forms stable protein aggregates as a result of binding of the polymer at a single site close to lysines 13, 86 and 87 on the protein surface (Concar et al., 1991). 

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