Glucansucrases: molecular engineering and oligosaccharide synthesis

Due to their informative role in biological systems, the potential development of oligosaccharide utilization is very important. Today, their industrial application is increasing rapidly especially for their capability of specific stimulation of beneficial bacteria. Future development will require the access to specific oligosaccharides synthesized via processes compatible with technical and economical industrial constraints. In this context, glucansucrases are attractive tools allowing the production of different glucooligosaccharides (GOS) from simple substrates such as sucrose and maltose. These bacterial enzymes are responsible for the synthesis of glucan polymers. They can also synthesize oligomers when an acceptor molecule is introduced into the medium. A large variety of glucosidic bonds are formed corresponding to variable regiospecificities dependent on the enzyme origin. More than 30 glucansucrase-encoding genes have been cloned and sequenced. Many data were provided from studies on the structure/function relationship on these sucrose-converting glucosyltransferases (GTF). Sequence alignment analysis allowed identification of essential amino acids and clearly showed analogies with enzymes from the large α-amylase family. It is now possible to list some determinants possibly involved in the glucansucrase specificity, but many additional investigations and data, especially about the three-dimensional structure, will be necessary for the rational design of specific enzymatic tools for GOS synthesis.