Solubility of peptide and its dissolution method

According to experience, the solubility of peptides is a very important link Improper dissolution may result in peptide loss or experimental failure The solubility of peptide depends on the sequence of peptide, so if the experiment allows, the peptide sequence should contain at least 20% charged residues to increase its solubility Before use, customers can follow the following three basic principles to choose the appropriate solvent to dissolve peptides First of all, the selected solvent must be able to fully dissolve the polypeptide Secondly, the selected solvent can be compatible with the experimental conditions After Zui, the selected solvent can not react with peptide or degrade peptide As long as the amount of peptide allows, it can be dissolved with a small amount of peptide first, and then all samples can be dissolved If the peptide needs to be recovered from the solvent, an initial solvent can be selected to make it easy to remove after freeze-drying The following suggestions may help you to dissolve peptides: 1 Peptides with less than 5 amino acids are generally soluble in aqueous solution, except for highly hydrophobic amino acids (W, I, l, F, m, V, y) 2 If the charged amino acids are evenly distributed in all sequences, the hydrophilic peptide containing > 25% charged amino acids (E, D, K, R, H) and the peptide containing < 25% hydrophobic amino acids can be generally soluble in aqueous solution The purification system of polypeptide is 0.1% TFA / water and 0.1% TFA / can Therefore, if the peptide is dissolved in a buffer with no or weak buffer capacity, the result may be that the peptide solution is acidic When using other methods to dissolve peptides, make sure that the pH value of the solvent is nearly neutral Acidic peptide (E + D residue is more than K + R + H residue) and alkaline peptide (K + R + H residue is more than e + D residue) are easier to dissolve at neutral pH than at acidic pH 3 The peptides with 50% - 75% hydrophobic amino acids may be insoluble in water or partially soluble even if they contain 25% charged amino acids Zui should first dissolve the peptide in a small amount of strong solvent (such as DMF, ACN, isopropanol, ethanol, acetic acid, 4-8M GdnHCl or urea, DMSO (when there is no C, W, m in the sequence), and other similar organic solvents Zui should slowly add the organic solvent to dissolve the peptide into the water solution drop by drop If the solution becomes turbid, it may reach the dissolution limit, and it is useless to continue to dissolve It should be noted that the solvents Zui started to choose should be compatible with the experimental system 4 Strong hydrophobic peptide with hydrophobic amino acid content more than 75% is generally insoluble in aqueous solution This kind of peptide should also be dissolved with strong solvent (such as TFA, formic acid) first If it is added to the aqueous solution, it may also produce precipitation The peptide solution after Zui may need a high concentration of organic solvent to denature it, while organic solvent is generally not used for the study of biological functions of living cells 5 S, T, E, D, K, R, H, N, Q, Y high (> 75%) polypeptide sequences are easy to form redundant intermolecular hydrogen bonding networks, and easy to form gels in concentrated aqueous solutions Such peptides can be dissolved by the method described in step 3 In order to reduce the possible problems in the dissolution, it is suggested that more consideration should be given to the design and sequence to improve the solubility of peptides It is a difficult problem for peptide researchers that which solvent is used to dissolve peptides According to different amino acid sequences, the following methods can be used to dissolve synthetic peptides Zui good is to dissolve a small amount of peptide in water solution first, do not dissolve all samples at once 1 The acid amino acids ASP (d), Glu (E) and c-cooh Were determined as - 1 2 The value of Arg (R), Lys (k), his (H) is + 1 3 Calculate the total charge in the peptide 4 If the total charge of the peptide is positive, the peptide is alkaline and can be dissolved with water first If the peptide is insoluble in water, it can be dissolved with 10% acetic acid or higher If the peptide is insoluble at all, add TFA (< 50 UL) to help dissolve and dilute to 1 ml with deionized water 5 If the total charge of the peptide is negative, the peptide is acidic and can be dissolved with water first If the peptide is insoluble in water, add NH4OH (< 50 UL) to help dissolve and dilute to 1 ml with deionized water 6 If the total charge of the peptide is 0, the peptide is neutral The neutral peptide needs to be dissolved in acetonitrile, methanol, isopropanol and other organic solvents, and can also be added with denaturants (such as urea, guanidine hydrochloride, etc.) Example: krlmksievimpl: (+ 3) + (- 2) = + 1 The peptide is alkaline See Step 4 above LVKMKSIEDPDCE: （+2） + （-5） = -3。 This peptide is acidic See Step 5 above MVSRKDLVEHRDM: （+4） + （-4） = 0。 This peptide is neutral See Step 6 above