Quantitative evaluation of the enhanced green fluorescent protein displayed on the cell surface of Saccharomyces cerevisiae by fluorometric and confocal laser scanning microscopic analyses

The number of foreign protein molecules expressed on the cell surface of th e budding yeast Saccharomyces cerevisiae by cell surface engineering was qu antitatively evaluated using enhanced green fluorescent protein (EGFP). The emission from EGFP on the cell surface was affected by changes in pH. The amount of EGFP on the cell surface, displayed as alpha -agglutinin-fusion p rotein under control of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH ) promoter, was determined at the optimum pH of 7.0. The fluorometric analy sis and the image analysis by confocal laser scanning microscopy (CLSM) sho wed a similar number of molecules displayed on the cell surface, demonstrat ing that 10(4)-10(5) molecules of alpha -agglutinin-fused molecules per cel l were expressed. Furthermore, the amount of fluorescent protein expressed on cells harboring a multicopy plasmid was three to four times higher than that on cells harboring the gene integrated into the genome.