Disulfide Bond
- Disulfide cross-links are where two cysteine residues form disulfide linkages.
- Although they are part of primary protein structure, they begin to provide the framework for the 3-dimensional shape of the protein because they lower the entropy of the unfolded protein, and thus destabilize it.
- Disulfide bonds form only between two cysteine residues because they have a sulfhydryl group as their side chain.
- Creation of disulfide bridges is considered oxidative – the hydrogen atoms on both cysteine residues are lost.
- Cysteine residues in a disulfide bond are called cystine.
- As a biochemical corollary, consider that strong reducing reagents such as beta-mercaptoethanol and dithiotheitol (DTT) break disulfide linkages.
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Amino Acid Modifications
AMINO ACID MODIFICATIONS
- Disulfide cross-linking (between two cysteine residues).
- Hydroxylation (the addition of a hydroxyl group).
- Carboxylation (the addition of a carboxyl group).
- Phosphorylation (the addition of a phosphate group).
- Methylation (the addition of methyl groups)
- Acetylation (the addition of acetyl groups)
- Glycosylation (the addition of sugars such as glucosamine or mannose)
- ADP-ribosylation (the addition of ADP-ribose)
- Ubiquitination (the addition of one or more ubiquitins)