Canonical heterotrimeric G proteins regulating mating and virulence of Cryptococcus neoformans.

Perturbation of pheromone signaling modulates not only mating but also virulence in Cryptococcus neoformans, an opportunistic human pathogen known to encode three Galpha, one Gbeta, and two Ggamma subunit proteins. We have found that Galphas Gpa2 and Gpa3 exhibit shared and distinct roles in regulating pheromone responses and mating. Gpa2 interacted with the pheromone receptor homolog Ste3alpha, Gbeta subunit Gpb1, and RGS protein Crg1. Crg1 also exhibited in vitro GAP activity toward Gpa2. These findings suggest that Gpa2 regulates mating through a conserved signaling mechanism. Moreover, we found that Ggammas Gpg1 and Gpg2 both regulate pheromone responses and mating. gpg1 mutants were attenuated in mating, and gpg2 mutants were sterile. Finally, although gpa2, gpa3, gpg1, gpg2, and gpg1 gpg2 mutants were fully virulent, gpa2 gpa3 mutants were attenuated for virulence in a murine model. Our study reveals a conserved but distinct signaling mechanism by two Galpha, one Gbeta, and two Ggamma proteins for pheromone responses, mating, and virulence in Cryptococcus neoformans, and it also reiterates that the link between mating and virulence is not due to mating per se but rather to certain mating-pathway components that encode additional functions promoting virulence.