Proteins polyelectrolytes self-assembly

Table 2 Some indicative examples of protein/polyelectrolytes self-assembly and generation of various supramolecular structures...

The electrostatic forces also play an important role in the conformation and structure of macromolecules such as polymers, polyelectrolytes, and proteins. The self-assembly of proteins from disks to virus is triggered by electrostatic interactions between neighboring subunits. In the case of polyelectrolytes (polymer molecules with charges) and charged colloids, transport behavior such as rheology is also affected significantly by charge effects, as we have already seen in Chapter 4. 

Biological macromolecules such as DNA and proteins are typical polyelectrolytes, which further hierarchically self-assemble into complicated supramolecular structures such as coiled coil (helix bundle) superstructures, which are responsible for their sophisticated functions [152,153]. Therefore, with implications for biological superstructures and functions, the design and synthesis of supramolecular helical assemblies with a controlled helicity have attracted great interest. 

Cationic polymers are of particular interest carriers in drug and gene deliveiy because of their ability to promote cellular uptake.This holds also for the delivery of proteins, especially for those that possess an overall anionic charge at pH values above the isoelectric point (p/). These proteins can form soluble, nanosized, polyelectrolyte complexes with natural or synthetic cationic polymers by simply mixing the oppositely charged protein and polymer that self-assemble by electrostatic attraction, as represented in Scheme 14.1. 

Several recent reviews deal with the fundamental self-assembly between proteins and natural polyelectrolytes, e.g. DNA and polysaccharides [30, 31, 34, 111], The applications in the food sector of protein and polysaccharide complexes and coacervates are also well covered elsewhere [35,112]. Given these abundant recent reviews, this field is deliberately excluded from the present review. 

Polyanions and polycations can co-react in aqueous solution to form polyelectrolyte complexes via a process closely linked to self-assembly processes [47]. Despite progresses in the field of (inter-) polyelectrolyte complexes [47] (IPEC from Gohy et al. [48], block ionomer complexes BIC from Kabanov et al. [49], polyion complex PIC from Kataoka and colleagues [50, 51], and complex coacervate core micelles C3M from Cohen Stuart and colleagues [52], understanding of more complex structures such as polyplexes (polyelectrolyte complexes of DNA and polycations) [53] is rather limited [54]. It has also to be considered that the behavior of cationic polymers in the presence of DNA and their complexes can be unpredictable, particularly in physiological environments due to the presence of other polyelectrolytes (i.e., proteins and enzymes) and variations in pH, etc. 

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