Modified peptides
For coupling carrier proteins to peptides, we recommends incorporating an N terminus cysteine for this reaction due to the high efficiency and proven effectiveness. For coupling through cysteine, we use MBS (maleimidobenzoic acid-N-hydroxysuccinimide ester) as a crosslinker. The initial step is to activate the protein with MBS, and then remove the excess crosslinker by SEC. This activated carrier protein is then coupled to the cysteine in the peptide through a disulfide bond with an efficiency of >95%. The only impurity in this reaction is salt formation, which CPC removes through gel filtration.
As an alternative to coupling through cysteine, we can additionally couple the carrier protein of choice through an amino link. The coupling efficiency of this reaction is generally around 80%. For carrying out this reaction, glutaraldehyde is used to crosslink the amino groups in both peptide and carrier protein. The most undesirable part of this reaction is the fact that protein-protein and peptide-peptide crosslinking can occur, and for this reason, the most important step is to insure that the proper concentration of crosslinker.
We offers a wide range of peptide modification services including the follwings:
1,KLH, BSA, and Ovalbumin
Peptide antigens are often too small to generate significant immune responses on their own. To solve this problem, these peptides are conjugated to bigger carrier proteins, such as bovine serum albumin (BSA), ovalbumin, or keyhole limpet hemocyanin (KLH). One of the advantages of KLH is that it does not interfere with ELISA or western blotting because it is not used as a blocking reagent. One common means of conjugation method is the maleimide method, which couples the cysteine residue of the peptide to the carrier protein. To perform this conjugation, one cysteine residue is added to the N- or C-terminus of the peptide so that it may be linked to the carrier protein.
Note: KLH is a large (MW = 4*105 to 1*107) aggregating protein. Because of its size and structure, its solubility in water is often limited, giving solutions and mixtures a cloudy appearance. This does not affect immunogenicity and the turbid solution can be used for immunizations.
2, Biotin and FITC
Fluorescein isothiocyanate (FITC) is an activated precursor used for fluorescein labeling. For efficient N-terminal labeling, a seven-atom aminohexanoyl spacer (NH2-CH2-CH2-CH2-CH2-CH2-COOH) is inserted between the fluorophore (fluoroscein) and the N-terminus of the peptide.
For C-terminal labeling of biotin, a Lys residue is added to the C-terminus of the peptide. Biotin is then attached to the lysine side chain via amide bond. The positive charge of the lysine is then removed.
3, Phosphorylation
Phosphopeptides can assist in the investigation of the influences of phosphorylation on peptides and protein structure and in the understanding of regulatory processes mediated by protein kinases. GenScript has successfully synthesized numerous serine-, threonine-, and tyrosine-phosphopeptides. For peptides containing one or more of these hydroxy-amino acids, selective phosphorylation can be achieved by orthogonal protection or by Fmoc-protected phosphorylated amino acids.
4, MAP Application
Multiple antigen peptide application is one potent way to produce high-titer anti-peptide antibodies and synthetic peptide vaccines. This system utilizes the a- and e-amino groups of lysine to form a backbone to which multiple peptide chains can be attached. Depending on the number of lysine tiers, different numbers of peptide branches can be synthesized. This eliminates the need to conjugate the antigen to a protein carrier.
5, Amidation and Acetylation
If the peptide is from an internal sequence of a protein, terminal amidation (C-terminus) or acetylation (N-terminus) will remove its charge and help it imitate its natural structure (amide, CONH2). In addition, this modification makes the resulting peptide more stable towards enzymatic degradation resulting from exopeptidases.
6. PEGylation
PEGylation is the covalent conjugation of macromolecules (antibody, peptide, etc.) with polyethylene glycol (PEG), polymers that are nonionic, nontoxic, biocompatible and highly hydrophilic. The PEGylated macromolecules have enhanced therapeutic properties due to their increased solubility (for hydrophobic drugs) and bioavailability, masked antigenicity for minimum immune response in host, prolonged circulatory time within host through reduced renal clearance.
7. Isotope Labeling
For NMR measurement, we can label peptides with stable nonradioactive isotopes. Peptides labeled with 2H, 15N, 13C, or both 15N and13C can be synthesized for convenient detection in research. Please submit your sequence and request for a customized labeling of your peptides.
8, Methylation
The methylation of proteins has been established as an important modification that helps regulate cellular functions such as transcription, cell division, and cell differentiation. Post-translational N-methylation usually occurs on lysine or arginine sidechains. Peptides that represent methylated proteins are useful for protein-protein interaction studies or structural determination by x-ray crystallography. We can synthesize peptides containing mono-, di-, and tri-methylated lysines at >98% purity, as well as other methylation combinations.
9, Cyclic Peptides Synthesis
Cyclic peptides are considerably more stable than linear peptides due to their resistance to proteases. They are of great interest to the biotechnology and pharmaceutical industries.
10, Tagged Peptides
Peptide tags are widely used in protein expression and purification, and also be used to protein detection through Western blot, ELISA, ChIP, immunocytochemistry, immunohistochemistry, and fluorescence measurement.
And etc.
