Isopeptide bond

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Figure 1: Locations of the epsilon Nitrogen, isopeptide bond, and peptide bond.

An Isopeptide bond is a chemical bond between a carboxyl group and an amino group. Isopeptide bonds are similar to peptide bonds that are found in amino acids except for which amino group participates in the bond. The difference is the ε-amino groups are used in the bond instead of the α-amino groups.

An Isopeptide bond usually occurs with the amino group of lysine or the carboxyl group of glutamate. In a peptide bond, which joins amino acids in a polypeptide, bonds form with the carboxyl and amino groups attached to a common alpha-carbon. With amino acids which happen to contain a carboxyl or amino group in their side chain, it is possible for an isopeptide bond to form.

An example of a small peptide containing an isopeptide bond is glutathione, which has a bond between the side chain of a glutamate residue and the amino group of a cysteine residue. An example of a protein involved in isopeptide bonding is ubiquitin, which gets attached to other proteins with a bond between the C-terminal glycine residue of ubiquitin and a lysine side chain of the substrate protein.

[edit] See also

• Organic Chemistry
• Biochemistry

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