Design scheme and solution of polypeptide peptide chain

I. Summary
Peptides are special macromolecules such that their sequences are unusual in their chemical and physical features. Some peptides are difficult to synthesize, while others are relatively easy to synthesize but difficult to purify. The practical problem is that most peptides are slightly soluble in aqueous solutions, so in our purification, the corresponding part of the hydrophobic peptide must be dissolved in non-aqueous solvents, Therefore, these solvents or buffers are likely to be severely inconsistent with the use of biological experimental procedures, so that technicians are strictly prohibited from using the peptide for their own purposes, so that the following are several aspects of the design of peptides for researchers.

Design scheme and solution of polypeptide peptide chain
Second, the correct choice of synthetic difficult peptides
1. Total length of down-regulated sequences
Peptides of less than 15 residues are easier to obtain because the size of the peptide increases and the purity of the crude product decreases. As the total length of peptide chain increases beyond 20 residues, precise product quantity is a key concern. In many experiments, it is easy to get unexpected effects by lowering the residue number below 20.
2. Decrease the number of hydrophobic residues
Peptides with a large predominance of hydrophobic residues, especially in the region 7-12 residues from the C-terminus, usually cause synthetic difficulties. This is seen as an inadequate combination precisely because a B-fold sheet is obtained in the synthesis. “In such cases, it may be useful to convert more than two positive and negative residues, or to put Gly or Pro into the peptide to unlock the peptide composition.”
3. Downregulation of “difficult” residues
“There are a number of Cys, Met, Arg, and Try residues that are generally not readily synthesized.” Ser will typically be used as a nonoxidative alternative to Cys.
Design scheme and solution of polypeptide peptide chain

Third, improve the correct choice of soluble in water
1. Adjust the N or C terminus
Relative to acidic peptides (that is, negatively charged at pH 7), acetylation (N-terminus acetylation,C terminus always maintaining a free carboxyl group) is particularly recommended to increase the negative charge. However, for basic peptides (that is, positively charged at pH 7), amination (free amino group at the N-terminus and amination at the C-terminus) is particularly recommended to increase the positive charge.

2. Greatly shorten or lengthen the sequence

Some of the sequences contain a large number of hydrophobic amino acids, such as Trp, Phe, Val, Ile, Leu, Met, Tyr and Ala, etc. When these hydrophobic residues exceed 50%, they are usually not easy to dissolve. It may be useful to lengthen the sequence to further increase the positive and negative poles of the peptide. The second option is to downregulate the size of the peptide chain to increase the positive and negative poles by downregulating the hydrophobic residues. The stronger the positive and negative sides of the peptide chain, the more likely it is to react with water.
3. Put in a water-soluble residue
For some peptide chains, the combination of some positive and negative amino acids can improve the water solubility. Our company recommends the N-terminus or C-terminus of acidic peptides to be combined with Glu-Glu. The N or C terminus of the basic peptide was given and then Lys-Lys. If the charged group cannot be placed, Ser-Gly-Ser can also be placed in the N or C terminus. However, this approach does not work when the sides of the peptide chain cannot be changed.