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Methylation is an important modification of proteins and nucleic acids, which is closely related to many diseases such as cancer and Alzheimer's disease, and is one of the important research contents of epigenetics. Methylation reactions are catalyzed by methyltransferases (MTs). The substrates that MTs act on can be nucleic acids or proteins. Methylation modification refers to the process of catalytically transferring methyl groups from active methyl compounds to other compounds, which can form various methyl compounds, or chemically modify certain proteins or nucleic acids to form methylated products.
Post-translational modifications (PTMs), as an important part of cell signaling pathways, are the molecular basis of protein dynamic responses and interactions, and are also important targets for cell signaling regulation. Methylation modification is a ubiquitous post-translational modification, which is involved in almost all life activities of cells and plays an important regulatory role. Protein methylation modification refers to the process of covalently binding proteins to specific amino acid residues under the catalysis of MTs. Methylation occurs mainly on arginine (Arg) and lysine (Lys) residues, but also on histidine, cysteine, and asparagine. Lys residues can be mono-, di-, or trimethylated. Arg residues can undergo mono- and di-methylation modifications. The latter can be asymmetric, i.e. both methyl groups are attached to the same N atom at the end of the Arg side chain, or symmetric, i.e. one methyl group is attached to each of the two terminal N atoms.
Histones are basic proteins in eukaryotic chromatin, rich in Arg and Lys. Epigenetically, methylation of Arg and Lys enables histones to epigenetically repress or activate gene expression.
Various covalent modifications can occur on histones. These modifications include methylation, phosphorylation, acetylation, ubiquitination, glycosylation, ADP ribosylation, and the like. Arg methylation of histones correlates with gene activation. Arg methylation of histones plays an important role in gene transcription regulation, chromatin remodeling, and certain aspects of gene expression.
Lys methylation of histones performs a variety of biological functions, including stem cell maintenance and differentiation, X chromosome inactivation, transcriptional regulation, and DNA damage response. Lys methylation of histones and DNA methylation have a mutual promotion effect. Histone methylation can guide DNA methylation. In turn, methylated DNA may also affect histone modifications.
Histone methylation
As histone methylation has been extensively studied, methylated peptides have become an important tool for studying histone methylation. Lys and Arg methylation modifications of peptides are currently achieved by applying methylated starting materials in peptide solid-phase synthesis. Lys(Me), Lys(Me)2, Lys(Me)3, Arg(Me), Arg(Me2, asymmetrical), Arg(Me2, symmetrical) These are particularly commonly used methylated peptide building blocks.
The main process for the synthesis of Lys and Arg methylated peptides is as follows:
Using Fmoc-Lys(Me,Boc)-OH, Fmoc-Lys(Me2)-OH, Fmoc-Lys(Me3)-OH.HCL, Fmoc-Arg(Me,Pbf)-OH, Fmoc-Arg(me)2 -OH.HCl(asymmetrical), Fmoc-Arg(me)2-OH.HCl(symmetrical) and other raw materials, and then synthesized by solid-phase synthesis technology to obtain Lys methylated and Arg methylated modified peptides. The product was finally purified using HPLC.
| Lys Mono-methylation | Lys Di-methylation | Lys Tri-methylation |
| Lys(Me) | Lys(Me2) | Lys(Me3) |
| Arg Mono-methylation | Arg Asymmetric Di-methylation | Arg Symmetric Tri-methylation |
| Arg(Me) | Arg(Me2, asymmetrical) | Arg(Me2, symmetrical) |
Methylated peptides are an important tool in the development of polyclonal antibodies and monoclonal antibodies. Methylation modifications change the structure of the polypeptide. Structural changes will lead to dramatic changes in the pharmacological activity of the modified polypeptides. For example, cyclic peptide compounds have the characteristics of good enzymatic stability, strong physiological activity and simple spatial structure. At the same time, natural polypeptides often contain N-methylated backbones and non-protein amino acids, which are beneficial to enhance their hydrolytic stability to proteases, membrane permeability and affinity to targets. N-methylated cyclic peptides combine the above two advantages and often have outstanding biological activities, so they become potential lead compounds for screening new drugs with antibacterial, antiviral, antitumor and immunomodulatory activities.
