Region of Flo1 proteins responsible for sugar recognition

Yeast flocculation is a phenomenon which is believed to result from an inte raction between a lectin-like protein and a mannose chain located on the ye ast cell surface. The FLO1 gene, which encodes a cell wall protein, is cons idered to play an important role in yeast flocculation, which is inhibited by mannose but not by glucose (mannose-specific flocculation). A new homolo gue of FLO1, named Lg-FLO1, was isolated from a flocculent bottom-fermentin g yeast strain in which flocculation is inhibited by both mannose and gluco se (mannose/glucose-specific flocculation). In order to confirm that both F LO1 and Lg-FLO1 are involved in the yeast flocculation phenomenon, the FLO1 gene in the mannose-specific flocculation strain was replaced by the Lg-FL O1 gene. The transformant in which the Lg-FLO1 gene was incorporated showed the same flocculation phenotype as the mannose/glucose-specific flocculati on strain, suggesting that the FLO1 and Lg-FLO1 genes encode mannose-specif ic and mannose/glucose-specific lectin-like proteins, respectively. Moreove r, the sugar recognition sites for these sugars were identified by expressi ng chimeric FLO1 and Lg-FLO1 genes. It nas found that the region from amino acid 196 to amino acid 240 of both gene products is important for floccula tion phenotypes. Further mutational analysis of this region suggested that Thr-202 in the Lg-Flo1 protein and Trp-228 in the Flo1 protein are involved in sugar recognition.