The protein phosphatase 2C domain contributes to the pathobiological function of adenylyl cyclase in Cryptococcus neoformans

Adenylyl cyclase (AC) is the central regulator of cAMP signalling in fungal pathogens, yet fungal ACs uniquely contain a protein phosphatase 2C (PP2C) domain whose function remains unclear. Here, we characterise the PP2C domain of the AC Cac1 in the human pathogen Cryptococcus neoformans . Structural and biochemical analyses show that Cac1-PP2C adopts a non-canonical scaffold but functions as a Ser/Thr-specific metalloenzyme. Deletion of the PP2C or AC catalytic (ACC) domain demonstrated that PP2C is required for full Cac1 activity, influencing melanin and capsule synthesis, sexual differentiation, titan cell formation, and cell wall integrity. Notably, the PP2C-null mutant induced Th2-biased immunity and extensive pulmonary damage yet failed to cause mortality in mice. Integrated transcriptomic and phosphoproteomic analyses further revealed shared and domain-specific signalling outputs mediated by PP2C and ACC. This study provides the first comprehensive characterisation of a fungal AC-linked PP2C domain and defines its pivotal role in C. neoformans pathobiology.