Ionic complementary peptides

A range of functionalized and unfunctionalized self-assembling fibrous structures have been tested for their biocompatibility and ability to provide cells with a favorable micro- and nanoenvironments for soft tissue engineering. In this section, studies that focus on amyloid fibrils, on peptide amphi-philes, on ionic complementary peptides, and on dipeptide structures are reviewed. Hard tissue engineering, composites, and coating are also explored followed by macroscopic structures and networks that can be created from fibrous protein structures. 

Ionic complementary peptides have been extensively examined for biocompatibility in a series of short-term in vitro and in vivo assays. The majority, but not all, of these studies have focused on two model systems RAD16 and EAK16. 

The properties of peptide fibers formed by ionic complementary peptides may need some tailoring to meet the different requirements for scaffolds and materials for drug delivery. Flowever, these roles could be quite complementary. It is easy to envisage that mixtures of peptide fibers with different stabilities could be used to simultaneously stimulate and support the growth of soft tissues. 

Figure 20.10. Amphiphilic ionic self-complementary peptides. This class of peptides has 16 amino acids, c. 5 nm in size, with an alternating polar and non-polar pattern. They form stable (3-strand and 3-sheet structures thus, the side chains partition into two sides, one polar and the other non-polar. They undergo self-assembly to form nanofibers with the non-polar residues inside positively and negatively charged residues form complementary ionic interactions, like a checkerboard. These nanofibers form interwoven matrices that further form a scaffold hydrogel with a very high water content ( 99.5%). The simplest peptide scaffold may form compartments to separate molecules into localized places where they can not only have high concentration, but also form a molecular gradient, one of the key prerequisites for prebiotic molecular evolution.

Altman, M., Lee, P., Rich, A., Zhang, S. Conformational behavior of ionic self-complementary peptides. Protein Sci. 9,1095-1105 (2000)... 

Salt (ionic strength) gradients in lEC discussed in Section 5.4.3.3 are frequently used in the separation of complex peptides, proteins, and other biopolymer samples as a complementary technique to RP solvent gradient separations, often in a 2D setup [99,100]. The gradients usually start at a low salt (chloride, sulfate, etc.) concentration and typically run from 0.005 to 0.5 M. A buffer is used to control the pH acetonitrile and methanol may be added to improve the resolution and urea to improve the solubility of proteins that are difficult to dissolve. Ion exchangers with not strongly hydrophobic matrices usually prevent protein denaturation in aqueous mobile phases. 

Figure 6.3 Self-assembled nanostructures based on P-sheet (a) peptides packing into sheets and fibers based on hydrophobic interactions on one face of the molecule, and complementary ionic interaction on the other (b) peptides with alternating hydrophilic and hydrophobic residues assemble into P-sheet structures (left) that form twisted ribbons (right) and bundle into larger fibers and (c) self-assembly based on amphiphilic triblock peptides, where the central hydrophobic block forces self-assembly via hydrophobic interactions between molecules and hydrogen bonding along the fiber axis.

A new type of self-assembling peptide nano-fibril that serves as a substrate for neurite outgrowth and synapse formation is described (Fig. 8). The selfassembling peptide scaffolds are formed through the spontaneous assembly of ionic self-complementary /1-sheet peptides under physiological conditions. 

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