Defence Chen Yang: "Structure–Function Relationship of Bacterial Glycogen Branching Enzymes"
Promotors: first promotor: Dr. Edita Jurak, second promotor: Prof. Mark van der Maarel
Abstract: Starch and glycogen are important energy-storage molecules in living organisms. Their structure contains many branches, and the number and length of these branches strongly influence their structure and metabolic properties as well as possible applications. The formation of these branches is catalyzed by glycogen branching enzymes.
Branching enzymes mainly belong to two subfamilies, GH13_8 and GH13_9. This thesis focuses on the poorly studied GH13_8 subfamily. Our studies show that GH13_8 enzymes mostly produce very short branches compared with the commercially used GH13_9 enzymes, which may provide advantages for industrial applications. However, enzymes from this subfamily often show relatively low activity, which limits their use. Therefore, understanding how their structure determines their function is important for rational enzyme engineering.
In this thesis, three key loops of the enzyme were identified that modulate branch formation and control the length of the branches. In addition, a previously uncharacterized groove responsible for binding the acceptor substrate was identified. This groove plays an essential role in positioning the sugar chain during branch formation. The work also revealed how structural features near the substrate entrance help the enzyme recognize and utilize short sugar chains. Together, these findings provide a detailed understanding of the relationship between structure and function in GH13_8 branching enzymes. This knowledge may support future efforts to engineer these enzymes for the production of tailored carbohydrate products with potential applications in food and biotechnology.