Proteinases and exopeptidases from the phytopathogenic fungus Ustilago maydis

The proteolytic system of the phytopathogenic and dimorphic fungus Ustilago maydis is not known. In this work, we report the presence of at least four proteases from two haploid strains of U. maydis. Activities of two proteinases pumA and pumB, aminopeptidase pumAPE, and dipeptidylaminopeptidase pumDAP were measured under several nutritional and morphological conditions, including the yeast-mycelium transition. The activity of pumA was found in the intracellular and extracellular fractions, pumAi and pumAe, respectively. The latter activity was detected only during the yeast-mycelium dimorphic transition induced by growth at acid pH in a medium containing ammonium as the sole nitrogen source. Activity of pumAe was partially inhibited by Pepstatin A, which also inhibited mycelium formation. Activity of pumAi was inhibited by this specific inhibitor of aspartyl-proteases. Activity of pumB was detected in intracellular and extracellular fractions, mostly bound to an endogenous inhibitor, which was removed by treatment at acid pH. This fungus contains at least two soluble pumAPE, which might be metallo-proteases, because they were inhibited by EDTA and 1-10, phenanthroline. When the fungus was grown in media containing proline or corn infusion as the nitrogen source, an intracellular pumDAP activity was detected. No carboxypeptidase activity was found with N-benzoyl-l-tyrosine-4-nitroanilide as substrate in any of the conditions tested in any of the U. maydis strains analyzed.