After understanding the reasons for peptide instability, confirmed based on years of experience in peptide synthesis that there are the following solutions to improve peptide stability.
1) Site directed mutation
Replacing residues that cause peptide instability or introducing residues that increase peptide stability through genetic engineering can improve peptide stability.
2) Chemical modification
There are many chemical modification methods for peptides, with PEG modification being the most studied. PEG is a water-soluble polymer compound that is biodegradable and non-toxic in vivo. PEG can improve the solubility of peptides after binding, regulate biocompatibility, enhance thermal stability, resist protease degradation, reduce antigenicity, and prolong the half-life in vivo. Choosing appropriate modification methods and controlling the degree of modification can improve physical fitness or enhance the original biological activity.
3) Additives
By adding additives such as sugars, polyols, gelatin, amino acids, and certain salts, the stability of peptides can be improved. Sugar and polyols force more water molecules to surround proteins at low concentrations, thereby improving the stability of peptides. During the freeze-drying process, the above-mentioned substances can also replace water and form hydrogen bonds with peptides to stabilize their natural conformation, and can also increase the glass transition temperature of freeze-dried products. In addition, surfactants such as SDS, Tween, Pluronic can prevent peptide surface adsorption, aggregation, and precipitation.
4) Freeze drying
The series of chemical reactions that occur in peptides, such as deamidation, beta elimination, hydrolysis, etc., require the participation of water, which can also serve as a mobile phase for other reactants. In addition, a decrease in water content can increase the denaturation temperature of peptides. Therefore, freeze-drying can improve the stability of peptides.