Opportunistic pathogens of the genus Candida cause infections representing a major threat to long-term survival of immunocompromised patients. Virulence of the Candida pathogens is enhanced by production of extracellular proteolytic enzymes and secreted aspartic proteases (Saps) are therefore studied as potential virulence factors and possible targets for therapeutic drug design. Candida parapsilosis is less invasive than C. albicans, however, it is one of the leading causative agents of yeast infections. Here we report three-dimensional crystal structure of Sapp2p from C. parapsilosis in complex with pepstatin A at atomic resolution 0.825 Å. The structure of Sapp2p was determined from protein isolated from its natural source and represents the structure on highest resolution of all aspartic proteases. Overall fold and topology of Sapp2p is very similar to the archetypic fold of monomeric aspartic protease family and known structures of Sap isoenzymes from C. albicans and Sapt1p from C. tropicalis.
Thanks to atomic resolution it was possible to assign protonation of functionally important side-chains. Positions of many hydrogen atoms was clearly visible from difference electron density map and the network of stabilizing hydrogen bonds became well guessable. New parallelized version SHELXL program allows us to use least squares spare matrix protocol to calculate ESDs of all refined parameters.