Citrullinated Peptide Synthesis
The amino acid citrulline is not coded for by DNA directly however several proteins are known to contain citrulline as a result of a posttranslational modification. These citrulline residues are generated by a family of enzymes called peptidylarginine deiminases (PADs), which convert arginine into citrulline in a process called citrullination or deimination. It has became clear in recent years that histones, fibronectin, myelin basic protein (MBP) as well as other cellular proteins can be modified by post-translational changes during epigenetic regulation in the cell. Modifications include acetylation, methylation, phosphorylation, ubiquitination and citrullination among others. Histone modifications induce changes to the struc¬ture of chromatin and thereby affect the accessibility of the DNA strand to transcriptional enzymes, resulting in activation or repression of genes associated with modified histones. So far citrulline modifications have been connected with the autoimmune disorders multiple sclerosis and rheumatoid arthritis. Biosynthesis offers citrulline incorporation into any peptide sequence to help researchers study the effect of these modifications in vivo or in vitro.
Deimination reaction of arginyl residues within peptide bonds Deimination of arginine results in neutral citrulline with the release of ammonia and the loss of one positive charge for each arginyl residue deiminated. The process is catalyzed by a calcium dependent peptidylarginine deiminase.
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