Structural and functional investigations of Lactobacillus reuteri glucansucrase : ... with crystallographic studies on an α-amylase and a prolyl endoprotease from Aspergillus niger

The main topic of this thesis are relatively large extracellular enzymes (~160kDa) named glucansucrases (GS)(EC 2.4.5.1) secreted by lactic acid bacteria. Using sucrose as a substrate they synthesize high molecular mass glucose polymers, called α-glucans. Additionally, in presence of suitable acceptor molecules (e.g. maltose) α-glyco-conjugates are synthesized at the expense of a polymeric product. Due to a vast product specificity of GH70 glucansucrases their products have markedly different properties which make them interesting targets for various industrial applications. Based on amino acid sequence similarity these enzymes (currently 60, CAZy database) have been classified in the Glycoside Hydrolase (GH) family, but no structural information on any of those has been available until now. Lack of structural data severely hampered in-depth understanding of the product specificity determinants of these enzymes.