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Posttranslational modification

From Academic Kids

Posttranslational modification means the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins.

Posttranslational modification may involve the formation of disulfide bridges and attachment of any of a number of biochemical functional groups, such as acetate, phosphate, various lipids and carbohydrates. Enzymes may also remove one or more amino acids from the amino end of the polypeptide chain, or cut the polypeptide in the middle of the chain. For instance, the peptide hormone insulin is cut twice after disulfide bond formation to remove a propeptide from the middle of the chain, leaving a protein consisting of two polypeptide chains connected by disulfide bonds. In other cases, two or more polypeptide chains that are synthesized separately may associate to become subunits of a protein with quaternary structure.

A protein is a chain composed of a long sequence of 20 possible amino acids, also called a polypeptide. Some posttranslational modification extends the range of possible functions a protein can have by introducing other chemical groups into the makeup of a protein (e.g., carbohydrate chains). Such chemical changes may alter the hydrophobicity of a protein and thus determine if the modified protein is cytosolic or membrane-bound. Other modifications like phosphorylation are part of common mechanisms for controlling the behavior of a protein, for instance, activating or inactivating an enzyme.

Types of posttranslational modifications include:

References

1. Van G. Wilson (Ed.) (2004). Sumoylation: Molecular Biology and Biochemistry (http://www.horizonpress.com/hsp/books/sumo.html). Horizon Bioscience. ISBN 0-9545232-8-8.

2. Malakhova, Oxana A.; Yan, Ming; Malakhov, Michael P.; Yuan, Youzhong; Ritchie, Kenneth J.; Kim, Keun Il; Peterson, Luke F.; Shuai, Ke; and Dong-Er Zhang. (2003). Protein ISGylation modulates the JAK-STAT signaling pathway (http://www.genesdev.org/cgi/content/full/17/4/455). Genes & Development 17 (4), 455-460.

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