You are what you secrete: extracellular proteins and virulence in Cryptococcus

Fungal organisms secrete a wide range of biomolecules, including degradative enzymes that are essential for nutrition, toxins, effectors and secondary compounds that modulate interactionswithhost animals andplants, anda variety of signaling and stress-related proteins. As these are likely to be key determinants of virulence and may also be useful diagnostic and therapeutic targets, we investigated the secretome of different strains of the fungal pathogen Cryptococcus. Virulent strains secreted predominantly hydrolytic and proteolytic enzymes, while the least virulent strain secreted a range of additional non-degradative proteins including many that lacked secretion signals, some that appear to be ‘moonlighting’, and a number that are known to be allergenic. It appears that in Cryptococcus, the secretomemay influence virulence both through the presence of harmful enzymes and through the absence of proteins that alert the host defence mechanisms.