Alginates are long chains of molecules composed of two similar sugar units called M and G. Alginates are found in many kinds of brown algae and are also produced by some bacteria. Alginates have been produced and used for many years as a gelling and thickening agent in food and industrial applications. In the latest years, also biomedical and pharmaceutical applications have been increasing. This has led to a need for alginate materials with specific and defined properties. In this respect, a class of enzyme proteins called alginate epimerases and alginate lyases are important tools. These proteins can change the ratio of M and G units (Ms converted to Gs) and the length of the alginate chains (introduce chain breaks) respectively. The M/G ratio and the chain length are the basic properties of alginates that decide the suitability for different applications, and thus controlling these properties are essential. Interestingly, the catalytic mechanism of epimerases and lyases, i.e. the specific way they are able to modify the alginate chains, are very similar even though their action lead to different end products. There are also examples of enzymes that can act as both epimerases and lyases. These intriguing properties are not fully characterised and a complete understanding of the mechanism of action of these enzymes are yet lacking. In this project, we will take advantage of the comprehensive competence on epimerases and lyases within the partners research groups and the availability of powerful experimental techniques for characterisation of the enzymes to gain insight into their complex functionality. The outcome of the project will have an impact on both basic and applied enzyme research by understanding the function of alginate epimerases and lyases in general. In addition, the knowledge can facilitate the development of new and improved functionalities of alginate modifying enzymes allowing for increased precision in the design of new alginate materials.
Alginates are high molecular weight polysaccharides composed of 1-4 linked residues of beta-D-mannuronic acid (M) and alfa-L-guluronic acid (G) and is produced by brown algae and some species of Pseudomonas and Azotobacter. Alginates are traditionally used as a gelling and thickening agent in food and industrial applications, but biomedical and pharmaceutical applications are increasing. This is accompanied with an increased need for alginate structures with specific and defined properties. In this respect, alginate epimerases and alginate lyases capable of modifying the M/G ratio and molecular weight respectively are important enzymatic tools. Interestingly, the catalytic mechanism of epimerases and lyases share common initial steps and one enzyme from A. vinelandii display both activities equally well probably originating from the same active site. Furthermore, recent research from the partners in the AlgModE consortium show that some alginate lyases occasionally also is able to perform epimerisation reactions. These intriguing properties are not fully characterised and a complete understanding of the catalytic mechanism of these alginate modifying enzymes are not yet understood. In the present project we will take advantage of the comprehensive competence on epimerases and lyases within the partners research groups as well as the availability of powerful techniques for structural and functional characterisation of the enzymes in order to gain insight into the complex reaction mechanisms. The expected outcome from this project will have impact for both basic and applied enzyme research by understanding the catalytic mechanism for alginate epimerases and lyases in general. In addition, the generated knowledge can facilitate development of new and improved functionalities of alginate modifying enzymes allowing for increased precision in tailoring of the biotechnologically important alginate polysaccharides.