Transferases in Polymer Chemistry - Enzymatic Polymerisation - page 27

Transglutaminases can recognize a broad range of primary amine acyl-acceptor
substrates in vitro. However, recognition of the acyl-donor substrate in vivo is re-
stricted to the

-carboxyamide of glutamine within an apparently relatively small
subset of sequence contexts
In vitro, the enzyme is able to catalyze crosslinking of whey proteins, soy pro-
teins, wheat proteins, beef myosin, casein, and crude actomyosin (which is refined
from mechanically deboned meat), improving functional properties such as the tex-
ture of food products [ 49 - 53 ] . Bonds formed by transglutaminase exhibit a high
resistance to proteolytic degradation [ 54 ].
Although the main applications of microbial transglutaminases remain in the
food sector, novel potential applications have emerged during the last decade. These
applications cover the areas of biomedical engineering, material science, textiles
and leather processing. For a recent excellent review by Zhu and Tramper see [ 55 ].
Transglutaminases can be used for improving the properties of protein-based fab-
rics such as wool, leading to a higher tensile strength after chemical or protease
pretreatment [ 56 , 57 ]. Besides crosslinking, transglutaminases were employed for
grafting/coating of wool fabrics with silk sericin or keratin, leading to increased
bursting strength and softness, and reduced felting shrinkage [ 58 , 59 ].
In biomedical applications, transglutaminases have been used for tissue engi-
neering materials such as enzymatically crosslinked collagen [ 60 - 63 ] or gelatin
scaffolds [ 64 - 69 ]. Even melt-extruded guides based on enzymatically crosslinked
macromolecules for peripheral nerve repair have been reported [ 70 ] .
Transglutaminases have just become recently available in larger quantities and
high purity due to microbiological production of the enzyme instead of extraction
from animal tissue. It can be expected that this enzyme will be used more frequently
in the future for food and non-food applications.

γ

3 Glycosyltransferases (EC 2.4)

Glycosyltransferases (GTs) are important biological catalysts in cellular systems,
generating complex cell surface glycans involved in adhesion and signaling pro-
cesses. Recent advances in glycoscience have increased the demand to access
significant amounts of glycans representing the glycome.
GTs catalyze the transfer of a sugar moiety from an activated donor sugar onto
saccharide and nonsaccharide acceptors. GTs can be divided into the Leloir and
non-Leloir types according to the type of glycosyl donors they use [ 71 ]. Non-Leloir
glycosyltransferases typically use glycosyl phosphates as donors, whereas Leloir
glycosyltransferases utilize sugar nucleotides as donors and transfer the monosac-
charide with either retention (retaining enzymes) or inversion (inverting enzymes)
of the configuration of the anomeric center. Most of the GTs responsible for the
biosynthesis of mammalian glycoproteins and glycolipids are Leloir GTs.
GTs now play a key role for in vitro synthesis of oligosaccharides, and the bac-
terial genomes are increasingly utilized for cloning and overexpression of active