The frequency of Candida infections has increased in recent years and it has been accompanied by a significant rise in morbidity and mortality. The secretion of aspartic proteases by Candida spp. was demonstrated to be one of the virulence determinants. Candida albicans is classified as the major human pathogen in the genus Candida. However, other species of this genus have been found to cause an increasing number of candidiases. We isolated secreted aspartic proteases (Saps) of C. albicans (Sap2p), C. tropicalis (Sapt1p), C. parapsilosis (Sapp1p), and C. lusitaniae (Saplp) from culture media. All the isolated proteases were N‐terminally sequenced. Their specific proteolytic activities and sensitivity to series of peptidomimetic inhibitors modified in the type of scissile bond replacement as well as in the N‐ and C‐termini were analyzed. The most divergent substrate specificity was observed for the Sap of C. tropicalis. The specificity of Sap of C. lusitaniae is most closely related to that of Sap of C. parapsilosis. We designed and prepared an inhibitor containing phenylstatine isoster that was equipotent towards all four proteases within the range of 10−10−10−9 m. The HIV‐1 protease inhibitors ritonavir, saquinavir, indinavir, and nelfinavir were also tested for the inhibition of four Saps. Only ritonavir and saquinavir inhibited Sap2p, Sapt1p, Sapp1p, and Saplp in micromolar concentrations.

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Human immunodeficiency virus (HIV) proteinase (PR) represents an important target for antiviral chemotherapy. We present an analysis of inhibitory activities of a series of pseudopeptide inhibitors of HIV-1 PR. All inhibitors were N-protected tetrapeptides with the scissile bond replaced by a nonhydrolysable hydroxyethylene or hydroxyethylamine isostere. To elucidate subtle structural requirements of the PR binding cleft, we synthesised inhibitors with four combinations of configurations at the asymmetric carbons of the isostere. Compounds were tested in vitro using purified recombinant enzyme and a chromogenic peptide substrate. The differences in inhibition constants between individual diastereoisomers reached three orders of magnitude. The most active hydroxyethylene-containing inhibitor possessed the 2R,4S,5S configuration at the isostere. Inhibitor activity was also tested in mammalian cell culture by analysing reduction of viral polyprotein processing and virus infectivity. The results obtained in tissue culture were generally in agreement with the in vitro data, giving a similar order of potency for the individual diastereoisomers. The most active compounds completely blocked production of infectious virus. A simulation method for interaction was employed to build a model of the inhibitors in the PR active site, to identify the interactions responsible for the differences in activities of individual stereoisomers, and to estimate the relative contribution of individual structural features to the overall inhibitory activity.

The yeasts of the genus Candida are opportunistic pathogens associated with the rising incidence of life-threatening infections in immunocompromised individuals. Secretion of aspartic proteinases has been determined to be one of the virulence factors of the pathogenic Candida species. To analyze the extracellular proteolytic activities of a large number of Candida clinical isolates, we developed a screening system based on a solid medium containing hemoglobin as the sole nitrogen source. The cleavage of hemoglobin by the secreted proteinases results in formation of clearance zones. The visibility of such zones was enhanced by addition of an acid-base indicator. Using this system, we assessed 245 clinical isolates of Candida from patients in the hospital of the Faculty of Medicine, Palacky University, Olomouc, Czech Republic, for the presence of secreted aspartic proteases (Saps). We also used the test plates for rapid semiquantitative testing of Sap inhibitors. Most of the pepstatin analogs affected the formation of the zones of clearance as well as the growth of Candida albicans, C. tropicalis, and C. parapsilosis colonies. By contrast, the human immunodeficiency virus proteinase inhibitors saquinavir, ritonavir, nelfinavir, and indinavir had no effect on the Candida strains tested. These results are in agreement with the inhibition constants obtained for the individual inhibitors with purified Saps. Thus, the plates containing hemoglobin proved to be an appropriate tool for the rapid and reliable assessment of Sap production and inhibition.The yeasts of the genus Candida are opportunistically invasive in individuals whose defense mechanisms are impaired. Pathogenic Candida species cause diseases ranging from superficial mycoses to disseminated and often fatal infections. The individuals at risk include intensive care and postsurgical patients, human immunodeficiency virus (HIV)-infected hosts, patients with hematological malignancies, elderly patients, and premature infants (4,6,18,25,28). Although Candida albicans is the most frequently isolated yeast associated with human infection, changing patterns of the Candida species detected among clinical isolates in the last decade are evident (5,8,24,28). Therefore, rapid and reliable identification of Candida species producing certain virulence factors is important in routine clinical microbiology practice.Virulence attributes of Candida species include adherence to host tissues, morphological changes, and secretion of hydrolases, e.g., phospholipases and proteinases (11). Secreted aspartic proteinases (Saps) of pathogenic Candida spp. have been studied extensively (13). C. albicans, C. tropicalis, C. dubliniensis, C. guilliermondii, and C. parapsilosis possess SAP gene families (7,10,13,16,30). The Saps of C. albicans, C. parapsilosis, C. tropicalis, and C. lusitaniae have been characterized (2,9,12,14,19,22,26), and their inhibitors have been tested as potential antimycotic drugs (for a review, see reference 27). Information on the extracellular proteolysis of o...

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