Each yeast cell builds its cell wall, an outer envelope that protects and shapes it. With the cell wall being the principal boundary between the cell and its environment, the cell shapes it meticulously, through intricate molecular mechanisms which are today only partially understood.
The yeast cell wall is made of an inner skeleton and an outer layer. While the inner skeleton is composed of ß-1,3- and ß-1,6-glucans, the outer layer is crafted from mannoproteins and their mannan chains. Some mannoproteins bind to glucan non-covalently, while others do so covalently, either by binding to ß-1,6-glucan through GPI anchor or to ß-1,3-glucan through characteristic Pir sequences. Such covalent binding can be used to immobilise novel, heterologous proteins to the surface of yeast cells, thus creating new biologically active materials. However, such newly-created cell surfaces sustain only low enzymatic activity.
To alleviate this shortcoming, we will modify the various molecular processes involved in the construction of the yeast cell wall, e.g. protein glycosylation and secretion, endocytosis, GPI anchor and native cell-wall protein binding. Moreover, we will expose on the yeast cell surface two biotechnologically noteworthy proteins, methionyl adenosine transferase (MAT) and sucrose phosphorylase (SPase). These two enzymes catalyse critical reactions in the production of S-adenosylmethionine and glucosylglycerol, two molecules today synthesised inside yeast cells, in the bioprocesses limited by the transport of required substrates into the cells. Thus, relocating the enzymatic reaction to the yeast surface would help the efficiency of the bioprocess.