TARGETING OF A HETEROLOGOUS PROTEIN TO THE CELL-WALL OF SACCHAROMYCES-CEREVISIAE

The sexual adhesion protein of Saccharomyces cerevisiae MATalpha cells, alpha-agglutinin, could not be extracted from the cell wall with hot sodium dodecyl sulfate (SDS), but became soluble after digestion of the cell wall with laminarinase. This indicates that it is intimately associated with cell wall glucan. A fusion protein was constructed consisting of the signal sequence of yeast invertase, guar alpha-galactosidase, and the C-terminal half of the alpha-agglutinin. Most of the fusion protein was incorporated in the cell wall. A small amount could be extracted with SDS, but most of it could only be extracted with laminarinase. On the other hand, cells containing a construct consisting of the signal sequence of invertase and alpha-galactosidase released most of the alpha-galactosidase into the medium and all cell wall-associated alpha-galactosidase was released by SDS. Labelling with antibodies showed that the alpha-galactosidase part of the fusion protein was exposed on the surface of the cell wall. The results demonstrate that the C-terminal half of the alpha-agglutinin contains the information needed to incorporate a protein into the cell wall.