Propping up our knowledge of G protein signaling pathways: diverse functions of putative noncanonical Gbeta subunits in fungi.

Heterotrimeric guanine nucleotide-binding proteins, composed of Galpha, Gbeta, and Ggamma subunits, are important mediators of fungal pheromone and nutrient signaling pathways. Most fungal genomes encode two or three functionally distinct Galpha subunits but only a single canonical Gbeta subunit, which does not bind multiple Galpha subunits. Studies in Saccharomyces cerevisiae, Cryptococcus neoformans, and Schizosaccharomyces pombe have identified binding partners for Galpha subunits, which are proposed to be "noncanonical Gbeta subunits." This Perspective reviews these studies, summarizing the strengths and weaknesses of the claims to this designation for these four fungal proteins.