Nao Kitahara

Comprehensive characterization of secreted aspartic proteases encoded by a virulence gene family in Candida albicans

Candida albicans is a commensal organism, but causes life-threatening infections in immunocompromised patients. Certain factors such as yeast-hyphae transition and hydrolytic enzymes are suggested as virulence attributes of C. albicans. Among them, 10 types of secreted aspartic protease (SAP) genes have received particular attention as a major virulence gene family. However, their full functional repertoire, including its biochemical properties, remains to be elucidated. Hence, we purified all Sap isozymes using Pichia pastoris and comprehensively determined and compared their biochemical properties. While optimum pH of Sap7 was 6.5 and that of Sap8 was 2.5, presence of other Sap isozymes functioning within a broad range of optimum pH could allow C. albicans to survive and cause infections in various tissues. The substrate specificities of Sap isozymes were analysed by using FRETS-25Xaa libraries. Sap7 and Sap10 showed high substrate specificity, while other Sap isozymes had broad substrate specificities. Principal component analysis revealed that the 10 Sap isozymes were clustered into 3 distinct groups in terms of their substrate specificities. Interestingly, Sap4-6, which are coproduced in the hyphal form, were clustered as the same group, indicating that they may target similar host proteins. These results will lead to further understanding of C. albicans pathogenicity.

Candida albicans possesses Sap7 as a pepstatin A-insensitive secreted aspartic protease.

Background Candida albicans, a commensal organism, is a part of the normal flora of healthy individuals. However, once the host immunity is compromised, C. albicans opportunistically causes recurrent superficial or fatal systemic candidiasis. Secreted aspartic proteases (Sap), encoded by 10 types of SAP genes, have been suggested to contribute to various virulence processes. Thus, it is important to elucidate their biochemical properties for better understanding of the molecular mechanisms that how Sap isozymes damage host tissues. Methodology/Principal Findings The SAP7 gene was cloned from C. albicans SC5314 and heterogeneously produced by Pichia pastoris. Measurement of Sap7 proteolytic activity using the FRETS-25Ala library showed that Sap7 was a pepstatin A-insensitive protease. To understand why Sap7 was insensitive to pepstatin A, alanine substitution mutants of Sap7 were constructed. We found that M242A and T467A mutants had normal proteolytic activity and sensitivity to pepstatin A. M242 and T467 were located in close proximity to the entrance to an active site, and alanine substitution at these positions widened the entrance. Our results suggest that this alteration might allow increased accessibility of pepstatin A to the active site. This inference was supported by the observation that the T467A mutant has stronger proteolytic activity than the wild type. Conclusions/Significance We found that Sap7 was a pepstatin A-insensitive protease, and that M242 and T467 restricted the accessibility of pepstatin A to the active site. This finding will lead to the development of a novel protease inhibitor beyond pepstatin A. Such a novel inhibitor will be an important research tool as well as pharmaceutical agent for patients suffering from candidiasis.

Time-course proteomic profile of Candida albicans during adaptation to a fetal serum

Candida albicans is a commensal organism; however, it causes fatal diseases if the host immunity is compromised. The mortality rate is very high due to the lack of effective treatment, leading to ceaseless demand for novel pharmaceuticals. In this study, time-course proteomics of C. albicans during adaptation to fetal bovine serum (FBS) was described. Time-course proteomics is a promising way to understand the exact process of going adaptation in dynamically changing environments. Candida albicans was cultivated in yeast nitrogen base (YNB) ± FBS media, and we identified 1418 proteins in the endpoint samples incubated for 0 or 60 min by a LC-MS/MS system with a long monolithic silica capillary column. Next, we carried out time-course proteomics of the YNB + FBS samples to identify top-priority proteins for adaption to FBS. We identified 16 proteins as nascent/newly synthesized proteins, and they were recognized as candidates of important virulent factors. Gene ontology analysis revealed that transport-related proteins were enriched in the 16 proteins, indicating that C. albicans probably put priority in time on the acquisition of essential elements. Time-course proteomics of C. albicans revealed the order of priority to adapt to FBS. Depicting time-course dynamics will lead to profound understandings of virulence of C. albicans.

Profiling of adhesive properties of the agglutinin-like sequence (ALS) protein family, a virulent attribute of Candida albicans.

Candida albicans is normally present in nearly all humans but can cause fatal diseases in immunocompromised patients. The agglutinin-like sequence (ALS) gene family of C. albicans has been suggested to be important for biofilm formation on medical devices. Here, we cloned all ALS genes and determined the binding properties of their gene products by cell surface engineering of Saccharomyces cerevisiae. Most of the ALS homologues had the ability to bind polypropylene, borosilicate glass and polyvinyl chloride, which are often used as materials in medical devices. However, ALS homologues were not able to bind polyurethane, polymethyl methacrylate, polytetrafluoroethylene or titanium. These findings will aid in the development of biofilm-resistant medical devices.

Elucidation of potentially virulent factors of Candida albicans during serum adaptation by using quantitative time-course proteomics.

UNLABELLED Candida albicans is an opportunistic pathogen that causes fatal disease if the host immunity is compromised. The mortality rate of systemic candidiasis is very high; hence, there is a ceaseless demand for novel pharmaceuticals. In this study, quantitative time-course proteomics of C. albicans during adaptation to fetal bovine serum (FBS) is described. Survival in blood is essential for virulence of C. albicans, and a detailed analysis is required. We cultivated C. albicans in FBS for 0-180min, and determined quantitative time-course variations of 1024 proteins in the cultured cells by using a LC-MS/MS system with a long monolithic silica capillary column. Clustering analysis identified FBS-induced proteins associated with detoxification of oxidative species, high-affinity glucose transport, citrate cycle, oxidative phosphorylation, and iron acquisition. Furthermore, we identified possible virulence factors such as orf19.4914.1 (named Blood-induced peptide 1, Blp1). Heterologous expression of BLP1 in Saccharomyces cerevisiae shortened the lag phase and resulted in a pleiotropic stress-tolerance phenotype, indicating a possible role for quick adaptation to a stressful environment. While further experiments are necessary to prove virulence of the identified factors, systematic identification of candidate virulence proteins in this study will lead to profound understanding of virulence of C. albicans. BIOLOGICAL SIGNIFICANCE This paper describes time-course proteomics of C. albicans during adaptation to serum, which is an essential process for fatal systemic candidiasis. Using a LC-MS/MS system with a monolithic silica capillary column, we have successfully characterized time-course variations of 1024 proteins. Among them, orf19.4914.1 (Blp1) was identified as a novel pleiotropic stress-tolerance peptide, which could have an important role for virulence of C. albicans.

Design of a Novel Antimicrobial Peptide Activated by Virulent Proteases

Antimicrobial peptides are promising antibiotics as they possess strong antimicrobial activity and very broad spectra of activity. However, administration of an antibiotic with a very broad spectrum of activity disrupts normal microflora and increases the risks of other fatal infections. To solve the problem, we designed a novel antimicrobial peptide that is activated by virulent proteases of pathogenic organisms. We constructed a peptide composed of three domains, namely an antimicrobial peptide (lactoferricin) as the active center, a protective peptide (magainin intervening sequence) that suppresses antimicrobial activity, and a specific linker that joins these two components and is efficiently cleaved by virulent proteases. We utilized Candida albicans as a model organism that produces secreted aspartic proteases as a virulence attribute. We screened for a peptide sequence efficiently cleaved by secreted aspartic proteases isozymes and identified a GFIKAFPK peptide as the most favorable substrate. Subsequently, we chemically synthesized a peptide containing the GFIKAFPK sequence. The designed peptide possessed no antimicrobial activity until it was activated by secreted aspartic proteases isozymes. Furthermore, it demonstrated selective antimicrobial activity against C. albicans, but not against Saccharomyces cerevisiae. A designed peptide like the one described in this study may protect normal microflora, resulting in enhanced safety as a therapeutic.