Transglutaminase enzymes couple or crosslink proteins in organisms by catalyzing transamidation of glutamine and lysine residues.

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"Biology is well known for its use of linear polymers to perform sophisticated functions. Nucleic acids store and process genetic information, while proteins perform recognition, transport, and catalytic functions. Biology also employs polymers (especially proteins and polysaccharides) to perform mechanical functions and there are several examples in which biology covalently crosslinks polymers to confer elasticity and strength. In some cases, the crosslinking enzymes have attracted attention as a simple and safe means for macromolecular processing in vitro. Here, we review recent research with two enzymes, tyrosinase and microbial transglutaminase, that are being examined for a variety of applications." (Yang et al. 2009:576)


Enzymes catalyze the cross-linking of natural polymers. Monomers (1) join together to form chains of polymers (2) that cross-link to form strong, large compounds (3). Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.

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"Transglutaminases crosslink proteins by catalyzing the transamidation of glutamine and lysine residues to form Ne-(c-glutamyl)lysine crosslinksVarious mammalian transglutaminases are known and they appear to perform a variety of functions in tissue [76–78]In the late 1980s, a screening effort in Japan yielded a microbial transglutaminase (mTG) that was smaller, had a broader substrate range [87], and was calcium independent [88]

"In summary, mTG offers a means to crosslink or couple proteins through accessible glutamine and lysine residues. Since mTG reacts with a broad range of primary amines (and not just lysine residues), this enzyme also allows small or large molecules to be grafted to proteins with residue-specificity. Importantly, mTG does not require reactive reagents or activated substituents and, thus, mTG provides a simple and safe method for coupling and crosslinking. As a result, the initial applications for mTG are expected to be in food, biotechnology, and medicine. However, the simplicity and residue-specificity of mTG suggest this enzyme can be used for the precise construction of macromolecular assemblies for a broader range of applications." (Yang et al. 2009:580-584)

Journal article
Crosslinking Lessons From Biology: Enlisting Enzymes for Macromolecular AssemblyThe Journal of AdhesionSeptember 4, 2009
Xiaohua Yang, Yi Liu, Gregory F. Payne

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