PTMs (Post-Translational Modifications)
Post-translational modifications (PTMs) such as protein phosphorylation, protein methylation or protein acetylation play an important role in virtually all biological processes. Therefore, the synthesis of post-translationally modified peptides (e.g. phosphopeptides or phosphorylated peptides, acetylated peptides, methylated peptides, peptides with citrulline or peptide glycosylation) is crucial for many projects.
JPT has extensive experience in the synthesis of a large variety of post-translationally modified peptides, eg. phosphopeptides. The following paragraphs describe examples of the most prevalent PTMs. However, there are many other post translational modifications that JPT can produce. JPT's experts will be happy to discuss your requirements.
Methylation at arginine or lysine residues is an important PTM of proteins. It is involved in the regulation of several cellular functions, for example transcription and cell division. One prominent example is the methylation and demethylation of histones. This process is regarded as a crucial mechanism in epigenetic regulation, as histone methylation and demethylation influences the availability of DNA for transcription.
Several methyl groups can be transferred to arginine or lysine (see tables below). JPT can provide all of the mono-, di- and tri-methylated Arg and Lys analogs listed below.
Other frequently occurring arginine post-translational modifications are the transformation to citrulline or nitration to nitro-arginine (see below).
Other Arginine Modifications
The methylation of lysine is, like arginine methylation, an important post-translational modification that is involved in a number of cellular processes. For example, histone methylation is involved in gene regulation. Therefore, the synthesis of peptides with site-specific Lys methylations is of great value for studying these processes. At JPT, we have extensive experience with the site-specific synthesis of mono-, di- and tri-methylated lysine peptides. Their respective structures and other frequently synthesized lysine PTMs are shown below.
All of these PTMs have been observed in histones and other proteins. They appear to play a critical role in gene expression and epigenetics. One notable exception is Lys(GG), which is formed by the tryptic digestion of ubiquitinylated peptides. The resulting peptide is a valuable reference standard for the determination of ubiquitinylation via proteomics workflows.
Other Lysine Modifications
Protein phosphorylation plays a major role in many physiological processes and is one of the most studied post-translational modifications. Among others, phosphorylation regulates cell cycle, apoptosis and signal transduction pathways. It occurs mainly on the hydroxyl side chain of Ser and Thr residues and, to a lesser extent, on the phenolic side chain of Tyr residues [Houben-Weyl, Methods in Organic Chemistry, Volume E22, Synthesis of Peptides and Peptidomimetics, Thieme Medical Publishers, 4th edition, 2002]. Phosphopeptides can function as control peptides for kinase profiling, as phosphatase substrates and as lead structures for phosphatase inhibitor discovery.
The site-specific synthesis of phosphorylated peptides is crucial for investigating phosphorylation events. Phosphorylated peptides are produced by:
(1) the specific incorporation of protected phospho-amino acids or
(2) the “post-assembly” phosphorylation of Ser/Thr/Tyr-containing peptide resins. Using the best suited approach for each peptide, JPT has successfully synthesized thousands of phosphopeptides in recent years.
In addition to traditional phosphopeptide synthesis, JPT provides a number of innovative solutions for kinase and phosphatase inhibitor design, screening and optimization, which are among the most efficient in industry.
See the following list for some examples:
- Kinase substrate microarrays– Screen >700 kinase substrates with extremely low sample requirement.
- Kinase substrate sets – Efficient kinase substrate screening.
- Positional scanning kinase substrate microarray and substrate sets – coming soon!
- Peptide optimization service– Discuss your kinase substrate optimization needs with us and collaboratively discover new substrates.
Phosphorylated peptides have limited stability in biological fluids due to the presence of phosphatases. To circumvent this problem, hydrolytically stable phosphate analogs can be incorporated into peptides. Here we show some examples of such phosphate mimetics.
Phospho Tyr Analogs
Phospho Ser/Thr Analogs
Depending on the peptide sequence and specification, JPT is able to incorporate the above mentioned analogs into many peptides. Please contact us to discuss all options.
Glycosylation is the most common posttranslational modification of proteins in eukaryotic cells. The carbohydrate portions of glycoproteins show a large diversity and play important roles in the distribution of these macromolecules within cells. In particular, they are recognition signals involved in intracellular communication, e.g. in cell adhesion, regulation of cell growth, infectious processes, and immunological differentiation [Houben-Weyl, Methods in Organic Chemistry, Volume E22, Synthesis of Peptides and Peptidomimetics, Thieme Medical Publishers, 4th edition, 2002].
Glycopeptides can be divided into two principal classes:
(1) N-linked and (2) O-linked glycopeptides.
(1) N-linked glycosylated peptides are the most frequently found glycopeptides. They contain an amide bond between a glycan and the side chain of Asp, the so-called N-glycosidic bond. The sites of N-glycosylation in N-glycoproteins are characterized by sequons Asn-Xaa-Ser/Thr (NXS/T, where Xaa is any amino acid except proline). The carbohydrate moiety is more variable, including alpha- and beta-Glc and beta-N-acetylgalactosamine (GalNAc). [Houben-Weyl, Methods in Organic Chemistry, Volume E22, Synthesis of Peptides and Peptidomimetics, Thieme Medical Publishers, 4th edition, 2002]
(2) O-linked glycoproteins are far more diversified than N-glycoproteins. The most abundant is the mucin-type with an alpha-linkage between GalNAc and serine or threonine. Examples of other saccharides linked to serine and threonine include alpha-galactose (Gal), glucose (Glc), fucose (Fuc), mannose (Man) and Xylose (Xyl). A separate class of O-linked glycosylation, which appears to be functionally distinct, is the O-GlcNAc modification found as monosaccharides attached to either Ser or Thr. [Houben-Weyl, Methods in Organic Chemistry, Volume E22, Synthesis of Peptides and Peptidomimetics, Thieme Medical Publishers, 4th edition, 2002]
A selection of glycosylated amino acids that have been successfully incorporated into peptides at JPT is shown below. Please contact us for your specific request.
Cys and Met Modifications
Cysteine-containing proteins can be modified in vivo in several ways (see below). Examples are oxidation reactions, leading e.g. to disulfides or cysteine sulfonic acid. Another example is Pam3Cys, which is a cysteine modification found in bacterial proteins and used for promoting immune stimulation.
For peptides used in proteomics experiments, cysteines are usually carbamidoylated. This can be done post synthesis using iodoacetamide, or by employing a suitable CAMC building block during synthesis.
The most frequently occurring PTM of methionine is oxidation. JPT routinely synthesizes all possible oxidation states (see below). To avoid undesired Met oxidation in peptides, we recommend exchanging Met with its isoster Nle (norleucine).
Sulfation and other PTMs
Tyrosine O-sulfation is a ubiquitous posttranslational protein modification that occurs in all multicellular organisms. Its functional importance is reflected by the fact that as much as 1 % of the total protein of an organism may be tyrosine O-sulfated. Apparently sulfation occurs exclusively on Tyr residues, although there are also indications of some Ser sulfation. [Houben-Weyl, Methods in Organic Chemistry, Volume E22, Synthesis of Peptides and Peptidomimetics, Thieme Medical Publishers, 4th edition, 2002]
While tyrosine-sulfated peptides are stable under basic conditions, the sulfate is unstable under acidic conditions. This makes the efficient synthesis of sulfated peptides technically challenging. JPT has established reliable procedures for the synthesis of sulfated peptides which guarantee high success rates. Based on this, we can supply a wide range of tyrosine-sulfated peptides depending on sequence and specification.
Examples of other naturally occurring modifications, which are routinely synthesized at JPT, are shown below. Please contact us if your post translational modification is not listed. We will be happy to evaluate all options and give you a quote.
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