The following peptide modifications are just examples.
Please contact us if a modification you need is not on the list.
Click on the modification for a detailed description.

Peptide modifications:

Acetylation/amidation of peptides

We can synthesize peptides with acetylated N-termini and/or amidated C-termini as part of our peptide synthesis process. Acetylation and amidation reduce the loadings of the termini, which is an advantage in some cases. An acetylated and amidated mimics an internal peptide sequence better than peptides with free termini. Acetylation and amidation also increase resistance to exonucleases, which can help in cell studies or in vivo experiments.

You can acetylate lysine(s) at the primary epsilon amino group (Lys(Ac)). Acetylation of lysine is relevant in, for example, epigenetics, where acetylated lysine helps bind peptides/proteins to DNA. Unlike methylated lysine, acetylated lysine carries no positive charge.

Azido-conjugated peptides
Peptides deliver with an azido group conjugated to the primary epsilon amino group on an inserted lysine or azido group conjugates as 5-azidopentanoic acid on the N-terminus.

Biotinylation of peptides

We can biotinylate peptides at the N-terminus or C-terminus. Biotin conjugates directly to the primary amino group on the N-terminus. We can also biotinylate peptides at the C-terminus via the primary amino group on a C-terminal inserted lysine.

Biotin has a strong affinity for streptavidin, making biotinylation an efficient method for binding peptides to streptavidin-coated surfaces. If the distance between biotin and the peptide matters, for example to avoid steric hindrance, CASLO offers different types of linkers to insert between biotin and the peptide sequence, such as aminohexanoic acid (Ahx) or 8-amino-3,6-dioxaoctanoic acid linker (miniPEG). Contact us to discuss which linker suits your application.

Branched Peptides

Interest in branched peptides has grown significantly in recent years. Branched peptides show several clinical effects in metabolism, especially as medicine against obesity, diabetes, and certain neurological diseases. We build branched sequences by attaching one or several peptides to the side chain of a lysine in the core sequence. The branches can include or exclude linkers and other modifications. CASLO has supplied hundreds of branched peptides for numerous applications.

Carrier protein KLH or BSA conjugated peptides and MAP
After peptide synthesis of peptides conjugates to the two carrier proteins KLH or BSA. Carrier proteins are conjugated via the side chain on an inserted cysteine. KLH or BSA conjugated peptides are primarily used for immunizations. Peptides are poor stimulators of the cell mediated immune response, but when peptides are conjugated to carrier protein, the cell mediated immune response is increased significantly.

There can only be one cysteine in the sequence if carrier protein shall be conjugated to the peptide. Please contact CASLO if you need assistance with finding the right sequence for immunization. If carrier proteins cannot be used for immunizations, peptide synthesis can designed where peptides are made as branched peptides (MAP) to increase the cell mediated immune response.

Cell penetrating peptides

Several cell penetrating amino acid sequences exist, and most carry a positive charge. You can use cell penetrating sequences as extensions to peptide sequences, making them more permeable to cell membranes. One example is the HIV-TAT sequence (GRKKRRQRRRPQ), which sits at the N-terminal part of a peptide — the most commonly used sequence among several options for making peptides more permeable to cells.

Other cell penetrating sequences include, for example, RRRRRRRR or LIKLWSHLIHIWFQNRRLKWKKK. Another way is to conjugate peptides to a fatty acid, like myristic acid, at the N-terminus. The fatty acid carries enough hydrophobicity to incorporate into the fatty acyl core of the phospholipid bilayer of the plasma membrane of eukaryotic cells. In this way, the fatty acid acts as a lipid anchor in biomembranes.

Click chemistry activated peptides
Peptides can be delivered conjugated to 5-azidopentanoic acid for “click chemistry”. Alternatively the azido group can be conjuagted to the primary amino group on an inserted lysine. The azido group reacts with alkynes in the presence of Cu/CuSO4 yielding triazoles. This is for example used for conjugation of peptides to alkyne conjugated DNA oligonucleotides. Propargylglycine can also be inserted in a peptide sequence during the peptide synthesis. Propargylglycine acts as an alkyne and the peptide can thereby be conjugated to azido-conjugated molecules.

Counterions
Peptides are in general delivered as trifluoroacetate (TFA) salts. These TFA salts can use for some cell cultures and a some type of in vivo experiments. There are however, cell cultures that are sensitive to the TFA counterion, and in some in vivo experiments TFA salts can not be used. For these applications CASLO recommend that peptides are delivered as chloride or acetate salts which are natural counterions.

Cyclization of peptides
Peptide synthesis are made where peptides are cyclized by disulfide bond(s) between cysteines or by amide bond between the N- and C-terminus. Amide bonds can be created on peptides from 5 and up to 20 amino acids, disulfide bonds also on longer peptides

D-Peptides
Peptides can be made with some or all of the amino acids in D-enantiomeric conformation. Amino acids in D-enantiomeric conformation are the mirror images of the natural L-enantiomers. D-enantiomeric amino acids are used for a range of applications. Most often D-amino acids are used to increase the resistance against a range of degradation enzymes. Such product containing D-amino acids are significantly more stable than peptide containing only L-amino acids. In some cases peptides containing D-amino acids furthermore have higher biological activity than the natural L-form, in other cases they have however, lower activity.

DOTA, DOPA and DTPA conjugated peptides
DOTA, DOPA and DTPA conjugated peptides are primarily used in renal science. The modifications can be made at the N-terminus or at the C-terminus via a C-terminal inserted lysine.

Fatty acid conjugated peptides
Fatty acid conjugated peptides can be used for a number of different applications, for example antibacterial activity or eukaryotic cell toxicity. Peptide synthesis can be arranged where fatty acids are conjugated to the N-terminus or the side chain of lysine. Peptides can be conjugated to fatty acids like: Caprylic acid (C8), Capric acid (C10), Lauric acid (C12), Myristic acid (C14), Palmitic acid (C16) or Stearic acid (C18) etc. A range of diacid versions of the fatty acids are also available.

Fluorochrome conjugated peptides

You can visualize fluorochrome conjugated peptides by fluorescence microscopy or other fluorescence visualization techniques. Our Team can conjugate peptides to fluorophores directly at the N-terminus during peptide synthesis (FITC always via an aminohexanoic acid (Ahx) linker). We can also conjugate to the C-terminus via an inserted lysine & deliver peptides conjugated to the following fluorochromes:

1- Fluorescein isothiocyanate (FITC): absorption (excitation) and emission spectrum peak wavelengths of approximately 495 nm/521 nm.
2- 5-(and-6)-Carboxyfluorescein (5-(and-6)-FAM, mixed isomer), also defined as 5,6-FAM: absorption (excitation) and emission spectrum peak wavelengths of 492/517 nm.
3- Carboxyfluorescein, also defined as 5-FAM: absorption (excitation) and emission spectrum peak wavelengths of 492/517 nm.
4- Rhodamine B: absorption (excitation) and emission spectrum peak wavelengths of 540/625 nm, respectively.
5- TAMRA: absorption (excitation) peak at 552 nm and emission peak at 578 nm. You can excite TAMRA using, for example, a 561 nm laser paired with a 582/15 nm bandpass filter.

Fluorescence/quencher pairs for FRET analysis
Peptides synthesis can be arranged where peptides are conjugated with fluorochromes and quenchers for FRET analysis. Fluorescence/quencher pairs must have a perfect spectral overlap between the emission spectrum of the fluorochrome and absorbance spectrum of the quencher.

When a fluorochrome and a quencher are conjugated to the same peptide, with a limited distance, the quencher blocks the emission of the fluorochrome. When however, the peptide is broken, for example by enzymatic degradation, the distance is increased and the fluorochrome is activated. The intensity of the fluorescence is therefore proportional with the degradation of the peptide.

The most commonly used fluorescence/quencher pair is EDANS/Dabcyl. Excitation and emission spectrum peak wavelengths of the EDANS fluorochrome are 336/490 nm respectively. Emission max for Dabcyl is 472 nm.

Formylation
Formylation of proteins or peptides has a wide range of applications in protein science. CASLO can deliver peptides formylated at the N-terminus, or at other locations via an inserted lysine.

Isotope labelled amino acids
Peptides can be made with a range of isotope labelled amino acids. Isotope labelled amino acids in protected form, and in high quality, which is used for peptide synthesis, are expensive, and isotope labelled peptides are therefore more expensive than standard peptides. The most economically isotope labelled amino acids are glycine and alanine. The most expensive are the amino acids with more complex side chains. CASLO do not recommend isotope labelling of more than one or two different amino acids in the sequence. Some of the amino acids labelled with one or more 13C and/or 15N isotopes which give different shifts in the molecular weight. Isotope labelling of peptides are typically used to track a peptide for example by mass spectrometry, but they can also be used for spiking or other applications.

Linkers
A number of different types of linkers can be inserted between active groups and the peptide sequence. For example a linker can be used to create a distance to biotin or a fluorochrome. The most commonly used linkers are aminohexanoic acid (Ahx) and 8-amino-3,6-dioxaoctanoic acid linker (also called OEG or miniPEG).

Methylated peptides
CASLO offers peptides with methylated lysines or arginines. During peptide synthesis, lysines can be mono-, di-, or trimethylated. Arginine can also undergo monomethylation as well as symmetric or asymmetric dimethylation. Methylated peptides support a number of applications. Methylated peptides and proteins play an important role in gene expression, as methylation of several proteins changes their binding affinity to DNA or alters the histone pathway.

Phosphorylated peptides
Peptides undergo phosphorylation on tyrosine, serine, or threonine residues. Peptides can contain one or two phosphorylation sites, while some peptides can contain more sites depending on the length and sequence.

Peptides conjugated to resin
Peptides can be delivered fully protected and conjugated to resin solid phase for further peptide synthesis or processing by customer. Detailed descriptions of the resin and detailed instructions for cleavage will be provided.

P-Nitroanilide / P-Nitroaniline (pNA)
Peptides uses synthesized with P-Nitroanilide in the C-terminal position. P-Nitroanilide is a substrate for certain proteases and peptides with C-terminal P-Nitroanilide are typically used in specific enzyme assays and when the enzyme releases P-Nitroaniline it can also meassured by colorimetric determination.

Selenopeptides
Peptides are made with selenomethionine or selenocysteine in the sequence. Selenopeptides and selenoproteins are used to study a large number of biological functions like protein folding, regulation of calcium homeostasis, cellular differentiation and several other biological functions. Furthermore selenopeptides are used in a diverse range of applications such as mechanistic probes, scaffolds, enzymatic reaction design, peptide conjugations and folding tools.

Side chain protected peptides
Peptides can delivered with side chain groups protected with various protection groups which can be removed: Cys(Acm) or Cys(tBu), Lys(Dde) (Lysine can also be delivered methylated or acetylated, but these groups cannot be removed) Met(Se).

Stabilization of reactive peptides
If the peptide sequence contains several cysteines, or other reactive amino acids, which are easily oxidized, CASLO offers to deliver the peptide with traces of the strong reductant DTT or alternatively TCEP. The peptide is only delivered with DTT or TCEP if this is specifically permitted by the customer.

Succinylated peptides
Peptides can make succinylated at the N-terminus. These succinylated peptides and proteins have a number of important functions in metabolism.

Sulfated peptides
Peptides can be sulfated by sulfation of tyrosine, Tyr(SO3H2). This sulfation of tyrosine increases interactions to other proteins or peptides. Proteins that are dependent on strong bonds to other proteins are therefore often sulfated, like adhesion proteins and proteins such as some receptors and hormones. It is only possible to make sulfation on short hydrophilic peptides.

Unnatural amino acids
It is possible to synthesize peptides with several unnatural amino acids, for example: D-amino acids, Abu, Ahx, Aib, Dab, Cit, Orn, pGlu, Hyp, Nal, Nle, Pip, Pyr, Tyr(3-NO2), Beta-Ala, Gamma-Glu and Tle. Several other unnatural amino acids are possible, please request.