Chemically synthesized peptides often carry free amino groups and free carboxyl groups.
The peptide sequence often represents the sequence of the maternal protein. In order to be closer to the maternal protein, the peptide end often needs to be closed, that is, N-terminal acetylation and C-terminal amidation.
The purpose of this modification is to reduce the total charge of the peptide, reduce the solubility of the polypeptide, and make the peptide simulate its original state of α – amino and carboxyl groups in the maternal protein.
We need to know that when the company receives the customized peptide demand, if the customer does not indicate that it needs N-terminal acetylation or C-terminal amidation, the N-terminal and C-terminal of the peptide chain synthesized in normal steps are bare.
Therefore, if it is necessary to acetyl the N-terminal or amide the C-terminal, it should be clear when ordering. Because once the composition is finished, it cannot be modified.
Peptide phosphorylation modification
Phosphorylated peptides mainly refer to the side chain hydroxyl groups of SER, Tyr and thr residues in the peptide chain, which are modified to acid phosphate polypeptides. Phosphorylated polypeptides are essential tools for the study of protein phosphorylation.
Therefore, it is very important to study the phosphorylation reaction of proteins and peptides and to determine a mature and simple synthetic route. Up to now, there are two main methods of phosphorylation modification: Post phosphorylation and monomer synthesis.
The post phosphorylation method is to phosphorylate the side chain hydroxyl of SER, Tyr or thr after the peptide sequence is synthesized on the resin; the monomer method is to directly introduce the phosphorylated amino acids with proper protection into the peptide sequence, which is more convenient than the post phosphorylation method, and has become the main method of peptide phosphorylation modification.
Is there a gap between the peptide and the dye?
Most biological reactive dyes belong to aromatic amino acids with high molecular weight. In order to avoid the interaction between the peptide and the tag and maintain the conformation and biological activity of the protein, Antonius bio recommends the introduction of a flexible spacer, such as AHX,. AHX is a cyclic structure containing 6 carbon molecules, which can maintain the stability of fluorescent tags.
If this spacer is not added in the synthesis, FITC can easily bind to cysteine or lysine residues in the peptide sequence.
In general, biotin, FITC and other dyes can be labeled on both the amino and carboxyl ends of proteins. However, in order to synthesize peptides in the shortest time and with the most convenient and efficient method, antolex recommends that customers choose to label the amino terminal.
Because the synthesis of a polypeptide usually starts from the carboxyl end, thus the modification of the amino terminal becomes the last step, and no special binding is needed. On the contrary, the carboxyl end modification requires additional steps, so the process is more complex.
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