The structure and function of three multimodular glycoside hydrolases related to cellulose, hemicellulose and pectin breakdown, and the influence of the accessory modules in the catalytic activity.

Abstract

Glycoside hydrolases (GH) are enzymes able to cleave the glycosidic bonds of different types of carbohydrates found in nature. Thanks to their activity, they became a research target in the production of second-generation ethanol. In this process, the fermentable sugars come from the breakdown of the polysaccharides present in the cell wall of plants. Since these polysaccharides form an intricate and recalcitrant network, several types of high efficient enzymes are required to achieve a cost-effective process. Most of GHs are modular enzymes composed of a catalytic domain and one or more accessory modules, for example, the carbohydrate-binding module, whose main function is to maintain the catalytic domain in proximity to the substrate, thus increasing its efficiency. Gradually, new modules with new features are being discovered, and the study and understanding of their functions is providing the development of enzymes with higher efficiency and new biotechnological applications. The objective of this project is to study the structure and function of three multimodular GHs, in order to reveal the influence of the accessory modules in the catalytic activity. The first one is a trimodular endoglucanase from Paenibacillus sp., composed of a catalytic domain, a CBM46 and another module (CBM_X2) that connects the others. The CBM_X2 still has its function unknown and previous results indicate that it has affinity for substrates. The second enzyme is a xylanase from family GH10 containing a CBM64. This CBM family is poorly characterized and previous results demonstrate, for the first time, a functional CBM in dimeric state at room temperature. In this way, we intend to determine its influence in the full-length enzyme activity. Finally, we intend to study an apiosidase from a mangrove metagenome that presents an unknown accessory module. The family to which this enzyme belongs was created recently, and little is known about them.