Peptide Conjugation – An Overview of Peptide Conjugates

Peptide conjugation is a strategy used to expand their utility in various fields including medicine, research and diagnostics. By conjugating peptides to a wide range of molecules, researchers can improve their stability, immunogenicity, targeting capabilities, as well as design useful research tools.

At AltaBioscience, our team provides high-quality custom peptides with a wide range of conjugation options and fast turnaround times to our clients worldwide. Contact our team to discuss your project or read on to explore our capabilities with 8 different ways we can conjugate peptides.

1. Biotinylated peptides

Biotin is a useful peptide tag that can be incorporated at the N-terminus or on a lysine residue at C-terminus or mid-sequence. In particular, biotin binds to the proteins avidin and streptavidin with the strongest known non-covalent bond. This bond is highly stable across a wide pH range (2-12) and only dissociates with the denaturation of streptavidin, making it highly specific. Biotinylated peptides are therefore powerful tools in biochemical research, enabling high-affinity interactions with streptavidin. For instance, they can be used in affinity purification, ELISA, and protein interaction studies.

2. Peptide oligonucleotide conjugates (POC)

Peptide oligonucleotide conjugates are hybrid molecules composed of a peptide linked to a single stranded oligo via a heterobifunctional linker. They are also known as POCs or DNA peptide conjugates and are widely used in drug discovery. One advantage is that the peptide and oligo moieties can be tailored to match the desired applications.  For instance, using cell-penetrating peptides can improve the deliverability of their cargos across cell membranes.

3. Peptide conjugation with dyes and quenchers

Fluorescent peptides

Fluorescent labelled peptides can be used in a wide range of applications, including fluorescence microscopy, flow cytometry, in vivo imaging and diagnostic assays. Conjugation of peptides with dyes are usually performed at the N-terminus. However, if the N-terminus is required for other use, then the labelling of the peptide can be performed on the side chain of a lysine residue.

Find below examples of commonly requested dyes: Dansyl, 5/6-FAM, TAMRA and Dylight^TM and FITC.

Quenchers

Contrary to fluorophores, quencher absorbs the light energy emitted by the latter, either by having an absorption spectrum which overlaps the emission wavelength of the fluorophore or by withdrawing this energy by direct contact of the two molecules.

FRET peptides

A common application of peptide conjugation with a dye and quencher pair is fluorescence resonance energy transfer (FRET, eg FAM-BHQ-1). When the donor and acceptor molecules are close (10Å–100Å), the donor’s emission overlaps with the acceptor’s absorption, quenching the signal. Intramolecularly quenched fluorogenic peptide substrates are valuable in biochemistry and enzyme assays. Indeed, upon hydrolysis, the donor and acceptor separate, increasing the donor dye’s fluorescence, which can be detected.

4. PEG peptide conjugates

PEGylated peptides are hybrid molecules composed of peptides linked to polyethylene glycol (PEG), a flexible and water-soluble polymer. The conjugation of PEG to peptides, a process known as PEGylation, imparts several beneficial properties to the peptides. By attaching PEG to peptides at various positions (e.g. N-terminus, Lys, Cys), peptide stability, solubility and bioavailability can be improved, as well as reducing immunogenicity and protease degradation. Our experts can perform site-specific PEGylation.

5. Peptide antigens

KLH peptides and other peptide-protein conjugates

Peptide antigens are often used for antibody generation. To enhance their immunogenicity, they can be conjugated to larger and more complex carrier proteins such as KLH (keyhole limpet hemocyanin), BSA (Bovine Serum Albumin) or ovalbumin. In return, this allows to form larger entities that efficiently stimulate the immune system. They are various chemistries available to form peptide-protein conjugates. One strategy is to use a heterobifunctional linker bearing N-hydroxysuccinimide ester (NHS) functional group and a maleimide group, hence allowing reactions with amino groups of the carrier protein and a thiol (-SH) group of a cysteine residue on the peptide respectively.

Multiple antigenic peptides (MAPs)

Alternatively, multiple antigenic peptides can be employed for the design of peptide antigens. These dendrimer structures, typically octameric with peptide chains branching out from a central poly-lysine core have an increased molecular weight that is usually sufficient to trigger an immune response.

6. Fatty acid peptide conjugation – Myristoylated Peptides

Myristoylation is a common post-translational modification where a myristoyl group (a 14-carbon saturated fatty acid) is conjugated to the N-terminal glycine residue of target proteins and peptides. Peptide conjugation to lipids increases their hydrophobicity. Therefore, this results in increasing their half-life as well as their membrane permeability and cellular uptake. For instance, in vitro fluorescence studies often use lipopeptides conjugated to fluorescent dyes.

7. Peptide-drug conjugates

Peptide-drug conjugates (PDCs) are a sub-class of drug conjugates that show great promise in targeted cancer therapies. They are composed of a short peptide, such as cell-penetrating or cell-targeting peptides, bound to a drug (e.g., cytotoxic payload, imaging reagents, radionucleotides) via a linker.

8. Synthetic peptides in lateral flow tests

Peptides are useful tools in diagnostics and in particular for the development of lateral flow tests. They can be conjugated to latex beads, bound to gold nanoparticles or used as antigens on the test line or for antibody generation. You can read more on our guest post: LFA DESIGN: HARNESSING THE POTENTIAL OF SYNTHETIC PEPTIDES.

Selected publications showcasing our peptide synthesis services

Find below some examples of our work cited in the literature. For more information, contact our team at info@altabioscience.com.