Making Proteins Sweeter

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Science  28 Feb 2003:
Vol. 299, Issue 5611, pp. 1283
DOI: 10.1126/science.299.5611.1283b

Many natural proteins are glycosylated, that is, they possess covalently bound sugar groups that can modify their stability, activity, and interactions with other biomolecules. The sugar groups can be highly variable even for the same protein, making it difficult to study their effects. To generate and study glycoprotein mimics, chemists have used the amino acid cysteine, which can be easily and selectively coupled to sugar groups. However, this method can become problematic if more than one cysteine is present in the target protein.

Two papers now show how the selective glycosylation of proteins can be facilitated through the use of an unnatural amino acid. Using a recently reported method for directly synthesizing unnatural amino acids in living cells, Wang et al. incorporated an amino acid containing a keto group (which is not present in natural amino acids) into proteins. Liu et al. then coupled sugar groups to the keto group in these proteins. The method yields homogeneous glycoprotein mimics with well-defined sugar groups and should be applicable to most proteins that can be expressed in Escherichia coli. — JFU

Proc. Natl. Acad. Sci. U.S.A. 100, 56 (2003), J. Am. Chem. Soc. 125, 1702 (2003).

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