Fungal lipopeptide mating pheromones: a model system for the study of protein prenylation

In a variety of fungal species, mating between haploid cells is initiated by the action of peptide pheromones. The identification and characterization of several fungal pheromones has revealed that they have common structural features classifying them as lipopeptides. In the course of biosynthesis, these pheromones undergo a series of posttranslational processing events prior to export. One common modification is the attachment of an isoprenoid group to the C terminus of the pheromone precursor. Genetic and biochemical investigations of this biosynthetic pathway have led to the elucidation of genes and enzymes which are responsible for isoprenylation of other polypeptides including the nuclear lamins, several vesicular transport proteins, and the oncogene product Ras. The alpha-factor of Saccharomyces cerevisiae serves as a model for studying the biosynthesis, export, and bioactivity of lipopeptide pheromones. In addition to being isoprenylated with a farnesyl group, the alpha-factor is secreted by a novel peptide export pathway utilizing a yeast homolog of the mammalian multidrug resistance P-glycoprotein. The identification of putative lipopeptide-encoding loci within other fungi, including the human immunodeficiency virus-associated opportunistic pathogen Cryptococcus neoformans and the plant pathogen Ustilago maydis, has stimulated much interest in understanding possible roles for pheromones in fungal proliferation and pathogenicity. Knowledge of variations within the processing, export, and receptor-mediated signal transduction pathways associated with different fungal lipopeptide pheromones will continue to provide insights into similar mechanisms which exist in higher eukaryotes.