fungal alpha-factor pheromone receptor STE2, member of the class D family of seven-transmembrane G protein-coupled receptors
This subfamily represents the alpha-factor pheromone receptor encoded by the STE2 gene, which is required for pheromone sensing and mating in haploid cells of the yeast Saccharomyces cerevisiae. The STE2-encoded seven-transmembrane domain receptor is a member of the class D GPCRs. Class D receptors are composed of two major subfamilies: Ste2 and Ste3. These two GPCRs (Ste2 and Ste3) sense the polypeptide mating pheromones, alpha-factor and a-factor, which activate a G protein-coupled receptors on the surface of the opposite yeast-mating haploid-types (MATa and MAT-alpha), respectively. Activation of these receptors by pheromones leads to activation of the mitogen-activated protein kinase (MAPK) signal transduction cascades, G1 cell cycle arrest, and polarized cell growth in the direction of the partner cell (a process called shmooing), which ultimately induces cell-cell fusion and the formation of a diploid zygote. Like all GPCRs, these pheromone mating factor receptors possess the same basic architecture of seven-transmembrane (7TM) domains and share common signaling mechanisms; however, there is no significant sequence similarity either between Ste2 and Ste3, or between these two receptors and the other 7TM GPCRs. Thus, STE2 and STE3 represent phylogenetically distinct groups.