The proteolytic system of the fission yeastSchizosaccharomyces pombe

Characterization of Aspartic Proteases from Paracoccidioides brasiliensis and Their Role in Fungal Thermo-Dimorphism

Paracoccidioidomycosis (PCM) is the most prevalent systemic mycosis in Latin America and is caused by fungi from the Paracoccidioides genus. The infection begins after inhalation of the fungal propagules and their thermo-dimorphic shift to yeast form. Proteases play an important role in the host invasion process and immune modulation in many pathogenic microorganisms. Aspartyl proteases are virulence factors in many human fungal pathogens that play an important role in the host invasion process morphogenesis, cellular function, immunity, and nutrition. In the present study, we characterized the modulation of acid proteases from Paracoccidioides brasiliensis. We detected four aspartyl proteases in P. brasiliensis with high homology to aspartic protease from Saccharomyces cerevisiae Pep4. Furthermore, we demonstrated that Pepstatin A can inhibit dimorphic switching (mycelium→yeast) in P. brasiliensis. In addition, these genes were modulated during thermo-dimorphism (M→Y transition) in the presence or absence of carbon and nitrogen sources and during growth at pH 4 during 24 and 48 h. We also observed that P. brasiliensis increase the secretion of aspartic proteases when cultivated at pH 4, and these acid proteases cleave BSA, collagen, and hemoglobin. These data suggest that aspartyl proteases are modulated by environmental conditions and during fungal thermo-dimorphism. Thus, this work brings new possibilities for studying the role of aspartyl proteases in the host-pathogen relationship and P. brasiliensis biology.

The pep4 gene encoding proteinase A is involved in dimorphism and pathogenesis of Ustilago maydis

Vacuole proteases have important functions in different physiological processes in fungi. Taking this aspect into consideration, and as a continuation of our studies on the analysis of the proteolytic system of Ustilago maydis, a phytopathogenic member of the Basidiomycota, we have analysed the role of the pep4 gene encoding the vacuolar acid proteinase PrA in the pathogenesis and morphogenesis of the fungus. After confirmation of the location of the protease in the vacuole using fluorescent probes, we obtained deletion mutants of the gene in sexually compatible strains of U. maydis (FB1 and FB2), and analysed their phenotypes. It was observed that the yeast to mycelium dimorphic transition induced by a pH change in the medium, or the use of a fatty acid as sole carbon source, was severely reduced in Δpep4 mutants. In addition, the virulence of the mutants in maize seedlings was reduced, as revealed by the lower proportion of plants infected and the reduction in size of the tumours induced by the pathogen, when compared with wild-type strains. All of these phenotypic alterations were reversed by complementation of the mutant strains with the wild-type gene. These results provide evidence of the importance of the pep4 gene for the morphogenesis and virulence of U. maydis.

Vacuolar proteases from Candida glabrata: Acid aspartic protease PrA, neutral serine protease PrB and serine carboxypeptidase CpY. The nitrogen source influences their level of expression

BACKGROUND

The Saccharomyces cerevisiae vacuole is actively involved in the mechanism of autophagy and is important in homeostasis, degradation, turnover, detoxification and protection under stressful conditions. In contrast, vacuolar proteases have not been fully studied in phylogenetically related Candida glabrata.

AIMS

The present paper is the first report on proteolytic activity in the C. glabrata vacuole.

METHODS

Biochemical studies in C. glabrata have highlighted the presence of different kinds of intracellular proteolytic activity: acid aspartyl proteinase (PrA) acts on substrates such as albumin and denatured acid hemoglobin, neutral serine protease (PrB) on collagen-type hide powder azure, and serine carboxypeptidase (CpY) on N-benzoyl-tyr-pNA.

RESULTS

Our results showed a subcellular fraction with highly specific enzymatic activity for these three proteases, which allowed to confirm its vacuolar location. Expression analyses were performed in the genes CgPEP4 (CgAPR1), CgPRB1 and CgCPY1 (CgPRC), coding for vacuolar aspartic protease A, neutral protease B and carboxypeptidase Y, respectively. The results show a differential regulation of protease expression depending on the nitrogen source.

CONCLUSIONS

The proteases encoded by genes CgPEP4, CgPRB1 and CgCPY1 from C. glabrata could participate in the process of autophagy and survival of this opportunistic pathogen.

Purification and comparison of intracellular proteinase A in Candida spp. isolates from Malaysian and Iranian patients and infected mice

OBJECTIVE

To compare the specific intracellular proteinase A activity in clinical isolates of Candida species isolated from Iranian and Malaysian patients, the blood and kidneys of mice infected by Candida cells isolated from these human patients.

PATIENTS AND METHODS

The intracellular proteinase A was extracted using glass beads and ultracentrifugation from yeasts cells and purified by ion-exchange chromatography (DEAE-cellulose), followed by affinity chromatography (ConA-agarose). Purity of proteinase A was controlled by SDS-PAGE and its identification was realized by western blot. Enzyme activity was performed using azocasein as substrate.

RESULTS

Intracellular proteinase A enzyme activity was higher in Candida albicans (C. albicans) than in non-albicans Candida isolates from Malaysian and Iranian patients, mice blood and mice kidneys (P<0.05). In clinical Candida spp. from human patients, proteinase A activity was significantly higher in Malaysian samples than in their Iranian counterparts (P<0.05). However, Candida spp. isolates obtained from blood and kidneys of mice infected by human clinical strains of Candida spp. showed no significant differences in proteinase A activity between Malaysian and Iranian samples (P>0.05). On the other hand, in both clinical and control yeast isolates obtained from Malaysian and Iranian patients, significant differences were found between systemic and non-systemic samples (P<0.05) but this difference was not observed in mice blood and kidneys.

CONCLUSION

In the present study, a strong proteinase A activity was observed for C. albicans and higher expression of this enzyme in clinical isolates from Malaysian and Iranian patients with systemic candidiasis indicated higher virulent nature of this yeast species when compared with non-albicans Candida strains.

Fission yeast and other yeasts as emergent models to unravel cellular aging in eukaryotes

In the past years, simple organisms such as yeasts and worms have contributed a great deal to aging research. Studies pioneered in Saccharomyces cerevisiae were useful to elucidate a significant number of molecular mechanisms underlying cellular aging and to discover novel longevity genes. Importantly, these genes proved many times to be conserved in multicellular eukaryotes. Consequently, such discovery approaches are being extended to other yeast models, such as Schizosaccharomyces pombe, Candida albicans, Kluyveromyces lactis, and Cryptococcus neoformans. In fission yeast, researchers have found links between asymmetrical cell division and nutrient signaling pathways with aging. In this review, we discuss the state of knowledge on the mechanisms controlling both replicative and chronological aging in S pombe and the other emergent yeast models.

Biochemical characterization and structural prediction of a novel cytosolic leucyl aminopeptidase of the M17 family from Schizosaccharomyces pombe

A new leucyl aminopeptidase activity has been identified in the fission yeast Schizosaccharomyces pombe. The enzyme, which has been purified and named leucyl aminopeptidase yspII (LAP yspII), had a molecular mass of 320 and 54 kDa by gel filtration and SDS/PAGE, respectively, suggesting a homohexameric structure. The enzyme cleaved synthetic aminoacyl-4-nitroanilides at an optimum of pH 8.5, and preferred leucine and methionine as N-terminal amino acids. A clear dependence on Mn2+ concentration for activity was found, and an apparent association constant of 0.33 mM was calculated for the metal ion. Bestatin behaved as a competitive inhibitor of LAP yspII (K(i) = 0.14 microM), while chelating agents such as chloroquine, EDTA and 1,10-phenanthroline also reduced enzyme activity. A MALDI-MS analysis, followed by sequencing of two of the resulting peptides, showed that LAP yspII undoubtedly corresponds to the putative aminopeptidase C13A11.05 identified in the S. pombe genome project. The protein exhibited nearly 40% sequence identity to fungal and mammalian aminopeptidases belonging to the M17 family of metallopeptidases. Catalytic residues (Lys292 and Arg366), as well as those involved in coordination with the cocatalytic metal ions (Lys280, Asp285, Asp303, Asp362 and Glu364) and those forming the hydrophobic pocket for substrate binding (Met300, Asn360, Ala363, Thr390, Leu391, Ala483 and Met486), were perfectly conserved among all known aminopeptidases. The S. pombe enzyme is predicted to be formed two clearly distinguished domains with a well conserved C-terminal catalytic domain showing a characteristic topology of eight beta-sheets surrounded by alpha-helical segments in the form of a saddle.

The intracellular proteolytic system of Yarrowia lipolytica and characterization of an aminopeptidase

Intracellular proteases of Yarrowia lipolytica have been scarcely studied. These enzymes may play an important role in nitrogen metabolism, posttranslational processing, nutritional stress, dimorphism, etc.; biochemical and genetic control of these enzymes can help in obtaining high-level expression of recombinant proteins in heterologous systems. In this study, we report the presence of three proteases: aminopeptidase yylAPE, carboxypeptidase yylCP and dipeptidyl aminopeptidase yylDAP, measured under several nutritional conditions. Yarrowia lipolytica produced the highest level of intracellular proteolytic enzymes, i.e. yylAPE, yylCP and yylDAP, in media with peptone during stationary growth phase. When soluble extracts were subjected to PAGE, and the three activities were revealed in gels with the corresponding substrates, only one band of activity was detected for each one. The three enzymes were affected by serine protease inhibitors. Chelating agents affected mainly APE activity. The aminopeptidase was purified by selective fractionation with ammonium sulfate and three chromatographic steps (anion exchange, hydrophobic interaction and gel filtration chromatography). The enzyme had a molecular mass of 97 kDa; optimal pH and temperature were 7.0 and 37 degrees C, respectively. The aminopeptidase showed a preference for lysine in the N-position. The K(m) value was 0.86 microM and V(max) value was 990.8 micromoL min(-1) mg(-1) for Lys-pNA.

Heterologous expression and characterization of Schizosaccharomyces pombe vacuolar carboxypeptidase Y in Saccharomyces cerevisiae

To investigate the intracellular transport mechanism of the vacuolar carboxypeptidase of Schizosaccharomyces pombe (SpCPY), SpCPY was expressed in Saccharomyces cerevisiae and its biosynthesis and sorting were examined. When Sac. cerevisiae prc1Delta, devoid of intrinsic (Sc) CPY activity, was transformed with a plasmid carrying the Sch. pombe cpy1(+) gene, CPY activity was restored. Pulse-chase experiments revealed that SpCPY is initially synthesized in a pro-precursor form and then converted to a heterodimer, the mature form, in Sac. cerevisiae cells. SpCPY was not processed into intermediate or mature forms in pep4 mutant cells, indicating that SpCPY was proteolytically cleaved in a PEP4-dependent manner in Sac. cerevisiae. Several vps mutants, which are defective in vacuolar protein-sorting, exhibited a defect in the maturation of SpCPY. Moreover, the maturation of SpCPY was severely inhibited in a vps10 strain, although the pro- segment of SpCPY does not contain a QRPL-like sequence, which is the putative targeting signal of ScCPY. When SpCPY was expressed in a wild-type strain, more than 90% of ScCPY was normally sorted to the vacuole, indicating that SpCPY does not compete with ScCPY for vacuolar sorting. In contrast, expression of SpCPY resulted in a missorting of a ScCPY-invertase fusion protein to the cell surface. These results suggested that there are two different binding sites for SpCPY and ScCPY on Vps10p and that the binding of SpCPY to Vps10p interferes with the binding of a ScCPY-invertase fusion protein.

The proteolytic system of the yeast Kluyveromyces lactis

Major proteolytic activities were characterized in the yeast K. lactis NRRL 1118, grown in chemostat cultures. This yeast expressed proteolytic activities similar to those found in S. cerevisiae. This fact was particularly evident in the case of proteases such as PrA, PrB and CpY with regard to substrate specificity, activation at pH 5. 0 and inhibition patterns. The presence of a CpS activity could not be detected in either fresh or activated cell-free extracts by using the dipeptide N-Cbz-Gly-Leu, even in the presence of Zn(+2). On the other hand, K. lactis exhibits at least two major intracellular Ap activities different from those reported in other yeasts, and these seem to be carried out by closely related proteins. These activities corresponded to molecular masses of about 60 kDa, close pI values, and a similar behaviour in non-denaturing polyacrylamide electrophoresis. Both activities were enhanced by Co(+2) and inhibited by EDTA. Among different aminoacyl-p-NAs, they preferentially hydrolysed Lys-p-NA. No increase of Ap activity was obtained by incubation of extracts at acid pH. The maximum PrA and PrB activities detected in N-limited cultures were six-fold higher than those expressed under C- or P-limitation. The effect of culture conditions on the Cp and Ap expression was much less pronounced in comparison with PrA and PrB activities, Ap levels even being slightly higher in C-limited cells. This fact suggests that hydrolysis of protein to peptides might be the limiting step in the pathway of general protein degradation in the vacuole.

Vacuolar carboxypeptidase Y of Saccharomyces cerevisiae is glycosylated, sorted and matured in the fission yeast Schizosaccharomyces pombe

Vacuolar carboxypeptidase Y of Saccharomyces cerevisiae (CPYsc) has been expressed in a Schizosaccharomyces pombe strain devoid of the endogenous equivalent peptidase, employing a 2 mu derived plasmid. Immunoblot analysis revealed that CPYsc produced in the fission yeast has a higher molecular mass than mature CPYsc produced by the budding yeast. CPYsc is glycosylated when expressed in S. pombe and uses four N-linked glycosylation sites as shown by endoglycosidase H digestion. Carbohydrate removal leads to a protein moiety which is indistinguishable in size from deglycosylated CPYsc produced by S. cerevisiae. CPYsc isolated from S. pombe soluble extracts is enzymatically active and thus is presumed to undergo correct proteolytic maturation. Subcellular fractionation experiments showed a cofractionation of CPYsc with the S. pombe endoproteinases PrA and PrB, suggesting that the protein is correctly sorted to the vacuole and that these peptidases might be responsible for zymogen activation.

Dipeptidyl aminopeptidase yspI mutants of Schizosaccharomyces pombe: genetic mapping of dpa1+ on chromosome III

A mutant strain of Schizosaccharomyces pombe lacking dipeptidyl aminopeptidase yspI was isolated from a strain already defective in aminopeptidase activity by means of a staining technique with the chromogenic substrate ala-pro-4-methoxy-beta-naph-thylamide to screen colonies for the absence of the enzyme. The defect segregated 2+:2- in meiotic tetrads, indicating a single chromosomal gene mutation, which was shown to be recessive. Gene dosage experiments indicated that the mutation resides in the structural gene of dipeptidyl aminopeptidase yspI, dpa1+. The dpa1+ gene was located on chromosome III by using m-fluorophenylalanine-induced haploidization and mitotic analysis. dpa1 mutants did not show any obvious phenotype under a variety of conditions tested.

Purification and characterization of aminopeptidase yspI from Schizosaccharomyces pombe

Aminopeptidase yspI was purified to apparent homogeneity from the fission yeast Schizosaccharomyces pombe. The molecular mass of the native enzyme was estimated to be 184 kDa by gel filtration chromatography. A value of 92 kDa was calculated after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme is thus a dimer with two identical subunits. Optimum pH for cleavage of synthetic aminoacyl-4-nitroanilides is 7.0. Mercury ions, EDTA and chloroquine were found to be potent inhibitors of aminopeptidase yspI activity. Substrate specificity studies indicate that the purified enzyme cleaves L-lysine-4-nitroanilide with high efficiency.

Purification and characterization of the endogenous inhibitor for proteinase B from Schizosaccharomyces pombe

A rapid purification procedure for the endogenous inhibitor of proteinase yspB from Schizosaccharomyces pombe is described. Starting from a boiled extract, the purification procedure included an ionic exchange chromatography and two reverse phase chromatographies using a HPLC system. The molecular mass of the purified polypeptide was estimated to be 8,100 Da by gel filtration. The isoelectric point of the inhibitor was found to be 5.3 after electrofocusing of a purified preparation. The amino acid composition of the proteinase yspB inhibitor was analyzed after acid hydrolysis. The calculated number of residues was 67 and the corresponding molecular mass 7370 Da. There are several differences in the molecular characteristics between the inhibitor from Schizosaccharomyces pombe and the corresponding inhibitor previously purified from Saccharomyces cerevisiae which might reflect the evolutionary divergence between the two yeast genera.