Structure/function relationships of glycogen branching enzymes

PhD ceremony: Ms. M. Palomo Reixach, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Structure/function relationships of glycogen branching enzymes

Promotor(s): prof. L. Dijkhuizen, prof. M.J.E.C. van der Maarel

Faculty: Mathematics and Natural Sciences

The new findings described in the thesis of Marta Palomo (which led to a patent application) are particularly valuable for understanding how glycogen is made and are important for developing new types of branched α -glucan polymers.

Glycogen is the major carbon and energy reserve polymer in cells of many animals and microorganisms. Lately glycogen has also been linked to several physiological processes such as cell differentiation, environmental survival, biofilm formation and virulence. One of the key enzymes involved in glycogen biosynthesis is glycogen branching enzyme (GBE) which catalyzes the formation of the α -1,6 branching points. The degree of branching and the length of the side-chains determine the physicochemical properties of the polysaccharides made. GBEs therefore hold great potential for new applications in the starch-related industry, with claims for GBE modified starch products in different areas, from bakery to paper coating.

Most GBEs belong to Glycoside Hydrolase family 13 (GH13) but recently they were also found in Glycoside Hydrolase family 57 (GH57). Palomo describes in her thesis the biochemical and structural analysis of GBEs from the GH13 and GH57 families. The functions of the different protein domains have been elucidated for both families of GBEs, and the identity of amino acid residues important for enzyme activity has been determined. Moreover, the first 3D structure of a GH57 GBE protein has been elucidated in collaboration with other researchers of the department Biophysical Chemistry.