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.
Biotin and FITC
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.
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.
Disulfide Bridge
Peptide cyclization can be achieved through creating disulfide bridges between
cysteine residues on the peptide. This is a challenging practice for peptide containing multiple
cysteine residues due to random formations of disulfide bridges between them. GenScript is able
to build disulfide bridges between cysteine at specified positions. We are able to introduce up
to three customized disulfide bridges on one peptide.
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.
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. GenScript can synthesize peptides containing mono-, di-,
and tri-methylated lysines at >98% purity, as well as other methylation combinations.
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.
Isotope Labeling
For NMR measurement, we can label peptides with stable nonradioactive isotopes.
Peptides labeled with 2H, 15N, 13C, or both 15N and 13C can be synthesized for convenient
detection in research.
MAPS
Multiple antigen peptide application is one potent way to produce high-titer
anti-peptide antibodies and synthetic peptide vaccines. This system utilizes the α- and ε-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.
BSA, KLH, and OVA Conjugation
Peptide antigens are often too small to generate significant immune responses on their own. To solve this problem, these peptides are conjugated to larger carrier proteins, such as bovine serum albumin (BSA), ovalbumin (OVA), or keyhole limpet hemocyanin (KLH). KLH is advantageous because it does not interfere with ELISA or western blotting, as it is not used as a blocking reagent. A common 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 for linkage.
Note: KLH is a large aggregating protein (MW = 4×10⁵ to 1×10⁷) with limited water solubility, which gives solutions a cloudy appearance. However, this does not affect immunogenicity, and the turbid solution can still be used for immunizations. For shipments, peptides are sent as solutions chilled with blue ice if precipitates form after conjugation.
Most Popular Reagents
Instruments
Antibodies
Protein Electrophoresis and Blotting
Molecular Biology
Stable Cell Lines
Cell Isolation and Activation
IVD Raw Materials
Therapy Applications
Resources
Pustovalova Y. et al. (2012) The C-terminal domain of human Rev1
contains independent
binding sites for DNA
polymerase Η and Rev7 subunit of polymerase Ζ. FEBS Lett. 586: 3051-3056. 
