Construction of engineered yeast with the ability of binding to cellulose

The genes encoding cellulose binding domain (CBD) from cellobiohydrolase I (CBHI) and cellobiohydrolase II (CBHII) of the filamentous fungus Trichoderma reesei were expressed on the cell surface of the yeast Saccharomyces cerevisiae by cell surface engineering. The CBD genes were fused to the gene encoding the Rhizopus oryzae glucoamylase secretion signal sequence, and expressed under the control of the glyceraldehydes-3-phosphate dehydrogenase (GAPDH) promoter. Each of CBDs was successfully displayed on the yeast cell surface by fusing their genes to the gene encoding the 3′-half of α-agglutinin of S. cerevisiae having a glycosylphosphatidylinositol anchor attachment signal. Tandemly aligned CBHI (CBD1) and CBHII (CBD2) fusion gene was also constructed to display simultaneously both CBDs on the cell surface of S. cerevisiae. Binding affinity of the CBD-displaying yeast cells to a cellulose substrate was similar between the CBD1- and CBD2-displaying yeast cells. However, the cells displaying the fusion protein of CBD1 and CBD2 showed much higher binding affinity to cellulose than either of the single CBD-displaying yeast cells. The binding affinity of the cells was increased by treating the cellulose with phosphoric acid.