O-GlcNAc and O-fucose binding plant lectins

Most proteins in a cell can be modified in a lot of different ways, for example in response to a change in environmental conditions or stress. Depending on their nature, these modifications can then change the function of the proteins in very diverse ways, or even inactivate them. One of these modifications is O-glycosylation, where certain sugar residues are attached to specific amino-acids of proteins. In plants, O-GlcNAcylation and O-fucosylation (attachment of either N-Acetylglucosamine or fucose) play an important role in this context. This kind of glycosylation is performed by only two specific O- glycosyltransferases, that modify a multitude of proteins that way. This modification plays a role in a number of very different processes, which is why plant cells need a way to differentiate in order to react accordingly and specifically. How this is achieved is currently not clear, but potentially an interaction between O-glycosylated proteins and lectins contributes to specificity in this context. Lectins are proteins that recognize and bind glycosylated proteins without further modifying them. This interaction can then further regulate the function of glycosylated proteins, for instance by affecting their localisation within the cell, or it can either facilitate or prevent their interaction with other proteins. Since plants carry many different lectins, they might provide an extra layer of complexity and thus specifically regulate O-glycosylation, leading to an adequate response to certain stimuli or regulate development in a flexible manner. During our work on O-glycosylation in plants, we have identified a small group of such lectins that might recognize specifically either O- GlcNacylation, O-fucosylation or both. The aim of the project presented here is to characterise these lectins and test, which sugars they bind well, or which glycosyltransferases they interact with. On the other hand, their biological role will be investigated in order to test if they are important for development and/or the response to certain environmental conditions. A second part of the project is dedicated to the identification of new lectins specifically binding O-glycosylated proteins. The results of this work will provide us with more information on the role of specific lectins and their interaction with O-glycosylation. Another important aspect here is that such lectins might be the basis for the development of new tools in order to analyse O-glycosylation specifically in plants, and maybe also other organisms. So far the methods to do so are limited, and developing new tools based on lectins would mean an important step forward in our attempt to understand the role of O-glycosylation in plants.

Most proteins in a cell can be modified in a lot of different ways, for example in response to a change in environmental conditions or stress. Depending on their nature, these modifications can then change the function or stability of the proteins in diverse ways. One of these modifications is O-glycosylation, where certain sugar residues are attached to specific amino-acids of proteins. In plants, O-GlcNAcylation and O-fucosylation (attachment of either N-Acetylglucosamine or fucose) play an important role in this context. This kind of glycosylation is performed by only two specific O-glycosyltransferases, that modify a multitude of proteins that way. The modification plays an important role in a number of very different processes, which is why plant cells need a way to differentiate in order to react accordingly and specifically. How this is achieved is currently not clear, but potentially an interaction between O-glycosylated proteins and lectins contributes to specificity in this context. Lectins are proteins that recognize and bind glycosylated proteins without further modifying them. This interaction can then further regulate the function of glycosylated proteins, for instance by affecting their localisation within the cell, or it can either facilitate or prevent their interaction with other proteins. Since plants carry many different lectins, they might provide an extra layer of complexity and thus specifically regulate O-glycosylation, leading to an adequate response to certain stimuli or regulate development in a flexible manner. During our work on O-glycosylation in plants, we have identified a small group of such lectins that might recognize specifically either O-GlcNAcylation, O-fucosylation or both. During this project, we characterized a small group of jacalin-like lectins (JALs), and could establish that they are active during seed germination and the response to drought. On a cellular level, we could confirm that they are found in the cytoplasm and the nucleus of cells, meaning that indeed they are active in the same compartments like O-GlcNAc and O-fucose modified proteins - unlike other common types of protein glycosylation. We also aimed to identify which carbohydrates are recognised by JALs, and found that they bind to a large number of proteins, as well as to several specific glycan structures. The results suggest that JALs bind to diverse carbohydrate structures, and that they potentially fulfil several roles in different parts of the cell. Further studies are necessary to identify the glycosylated proteins bound by JALs, in order to better understand their role during seed germination and drought response.