Team:UCSF/ProjectOverview

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Queen's

Background

Agglutination, a type of aggregation specific to mating in Sacchromyces cerevisiae, occurs with two surface proteins: alpha-agglutinin and a-agglutinin. Alpha-agglutinin is produced only by alpha-cells and a-agglutinin is produced only by a-cells. During mating, each cell releases pheromones and accepts pheromones secreted by other cells. The alpha-cells respond to a-cell pheromones while the a-cells respond to alpha pheromones. When each cell has received enough of the correct molecule, it will begin to make its agglutinin. In close proximity, the alpha-agglutinin and the a-agglutinin will aggregate, causing cell-cell adhesion. The two yeast cells will come close enough and eventually fuse into one diploid cell.

We took a closer look into the protein, a-agglutinin, and found that it was composed of two subunits: Aga1p and Aga2p. The Aga1 and Aga2 genes lie under a promoter that switches on when the cell has received pheromones from a mate. When the proteins are expressed, Aga1p is attached to the cell surface by a GPI anchor and is also connected to Aga2p through disulfide bonds.

For our project, we decided to utilize the a-agglutinin half of the aggregation display system to form artificial biofilms. By placing sequences of strong adhesive proteins behind the GPI anchor-Aga1-Aga2 gene and overexpressing them, we were able to create yeast cells that could adhere to different surfaces and even other yeast cells. A couple genes we used to attach to the end of the Aga1p-Aga2p complex were mice cadherins, proteins that mussels used to stick to rocks, and proteins used by other yeast species to initiate biofilm formation.

Yeast Cell Surface Display Yeast Cell Surface Display