Purification and characterization of a 315 kDa keratinolytic subtilisin-like serine protease fromMicrosporum canisand evidence of its secretion in naturally infected cats

Fungal alkaline proteases and their potential applications in different industries

The consumption of various enzymes in industrial applications around the world has increased immensely. Nowadays, industries are more focused on incorporating microbial enzymes in multiple processes to avoid the hazardous effects of chemicals. Among these commercially exploited enzymes, proteases are the most abundantly used enzymes in different industries. Numerous bacterial alkaline proteases have been studied widely and are commercially available; however, fungi exhibit a broader variety of proteases than bacteria. Additionally, since fungi are often recognized as generally regarded as safe (GRAS), using them as enzyme producers is safer than using bacteria. Fungal alkaline proteases are appealing models for industrial use because of their distinct spectrum of action and enormous diversity in terms of being active under alkaline range of pH. Unlike bacteria, fungi are less studied for alkaline protease production. Moreover, group of fungi growing at alkaline pH has remained unexplored for their capability for the production of commercially valuable products that are stable at alkaline pH. The current review focuses on the detailed classification of proteases, the production of alkaline proteases from different fungi by fermentation (submerged and solid–state), and their potential applications in detergent, leather, food, pharmaceutical industries along with their important role in silk degumming, waste management and silver recovery processes. Furthermore, the promising role of alkali–tolerant and alkaliphilic fungi in enzyme production has been discussed briefly. This will highlight the need for more research on fungi growing at alkaline pH and their biotechnological potential.

Current Topics in Dermatophyte Classification and Clinical Diagnosis

Dermatophytes are highly infectious fungi that cause superficial infections in keratinized tissues in humans and animals. This group of fungi is defined by their ability to digest keratin and encompasses a wide range of species. Classification of many of these species has recently changed due to genetic analysis, potentially affecting clinical diagnosis and disease management. In this review, we discuss dermatophyte classification including name changes for medically important species, current and potential diagnostic techniques for detecting dermatophytes, and an in-depth review of Microsporum canis, a prevalent zoonotic dermatophyte. Fungal culture is still considered the “gold standard” for diagnosing dermatophytosis; however, modern molecular assays have overcome the main disadvantages of culture, allowing for tandem use with cultures. Further investigation into novel molecular assays for dermatophytosis is critical, especially for high-density populations where rapid diagnosis is essential for outbreak prevention. A frequently encountered dermatophyte in clinical settings is M. canis, which causes dermatophytosis in humans and cats. M. canis is adapting to its primary host (cats) as one of its mating types (MAT1-2) appears to be going extinct, leading to a loss of sexual reproduction. Investigating M. canis strains around the world can help elucidate the evolutionary trajectory of this fungi.

Genetic Characterization of Microsporum canis Clinical Isolates in the United States

Microsporum canis is the primary agent causing dermatophytosis in cats, and also infects humans, dogs, and other species. Assessment of genetic variation among M. canis isolates in the United States has not been conducted. Further, M. canis mating type and assessment of disease severity associated with genotypic characteristics have not been rigorously evaluated. We therefore isolated M. canis from 191 domestic cats across the US and characterized genotypes by evaluation of ITS sequence, MAT locus, and microsatellite loci analysis. The genes SSU1 and SUB3, which are associated with keratin adhesion and digestion, were sequenced from a subset of isolates to evaluate potential genetic associations with virulence. Analysis of microsatellite makers revealed three M. canis genetic clusters. Both clinic location and disease severity were significant predictors of microsatellite variants. 100% of the M. canis isolates were MAT1-1 mating gene type, indicating that MAT1-2 is very rare or extinct in the US and that asexual reproduction is the dominant form of replication. No genetic variation at SSU1 and SUB3 was observed. These findings pave the way for novel testing modalities for M. canis and provide insights about transmission and ecology of this ubiquitous and relatively uncharacterized agent.

Comprehensive Assessment of the Virulence Factors sub 3, sub 6 and mcpA in the Zoonotic Dermatophyte Trichophyton benhamiae Using FISH and qPCR

Skin infections by keratinophilic fungi are commonly referred to as dermatophytosis and represent a major health burden worldwide. Although patient numbers are on the rise, data on virulence factors, their function and kinetics are scarce. We employed an ex vivo infection model based on guinea pig skin explants (GPSE) for the zoonotic dermatophyte Trichophyton (T.) benhamiae to investigate kinetics of the virulence factors subtilisin (sub) 3, sub 6, metallocarboxypeptidase A (mcpA) and isocitrate lyase (isol) at gene level for ten days. Fluorescence in situ hybridization (FISH) and quantitative polymerase chain reaction (qPCR) were used to detect and quantify the transcripts, respectively. Kingdom-spanning, species-specific and virulence factor-specific probes were successfully applied to isolated fungal elements showing inhomogeneous fluorescence signals along hyphae. Staining results for inoculated GPSE remained inconsistent despite thorough optimization. qPCR revealed a significant increase of sub 3- and mcpA-transcripts toward the end of culture, sub 6 and isol remained at a low level throughout the entire culture period. Sub 3 is tightly connected to the de novo formation of conidia during culture. Since sub 6 is considered an in vivo disease marker. However, the presented findings urgently call for further research on the role of certain virulence factors during infection and disease.

Recent advances in fungal serine protease inhibitors

Four types of antifungal drugs are available that include inhibitors of ergosterol synthesis, of fungal RNA biosynthesis, and of cell wall biosynthesis as well as physiochemical regulators of fungal membrane sterols. Increasing resistance to antifungal drugs can severely limit treatment options of fungal nail infections, vaginal candidiasis, ringworm, blastomycosis, histoplasmosis, and Candida infections of the mouth, throat, and esophagus, among other infections. Development of strategies focused on new fungicides can effectively help tackle troublesome fungal diseases. The virulence and optimal growth of fungi depend on various extracellular secreted factors, among which proteases, such as serine proteases, are of particular interest. A specific extracellular proteolytic system enables fungi to survive and penetrate the tissues. Given the role of fungal proteases in infection, any molecule capable of selectively and specifically inhibiting their activity can lead to the development of potential drugs. Owing to their specific mode of action, fungal protease inhibitors can avoid fungal resistance observed with currently available treatments. Although fungal secreted proteases have been extensively studied as potential virulence factors, our understanding of the substrate specificity of such proteases remains poor. In this review, we summarize the recent advances in the design and development of specific serine protease inhibitors and provide a brief history of the compounds that inhibit fungal serine protease activity.

Detection of subtilisin 3 and 6 in skin biopsies of cattle with clinically manifested bovine ringworm

Trichophyton (T.) verrucosum is a highly pathogenic dermatophyte causing zoonotic bovine ringworm that is transmissible to humans. The virulence factors subtilisin (Sub)3 and Sub6 are discussed to contribute to disease manifestation but no protein expression study is available for T. verrucosum. We used customized antibodies (against Trichophyton-species, Sub3 and Sub6) to examine skin biopsies of infected cattle via immunofluorescence stainings. Both virulence factors Sub3 and 6 were solely expressed by conidia and not only found in epidermal but also in dermal and hair structures. The anti-T-antibody reliably detected the fungus and proved more sensitive compared to histological stains.

LAY SUMMARY

We examined the zoonotic dermatophyte Trichophyton (T.) verrucosum in bovine skin and studied two important virulence factors called subtilisin (Sub)3 and Sub6 that T. verrucosum produces and secretes using immunolabeling.

Comparative Analysis of Putative Virulence-Associated Factors of Microsporum canis Isolates from Human and Animal Patients

Microsporum canis is a zoophilic dermatophyte and the most common fungus isolated from dogs and cats worldwide. To invade skin, this pathogen uses different enzymes, which may be associated with virulence, that contribute to the fungal pathogenicity. The aim of this study is to compare the expression of enzymes that may be associated with virulence, and thermotolerance of M. canis strains isolated from dogs, cats, and humans. The in vitro expression of the enzymes keratinase, catalase, urease, hemolysin, and aspartic protease was evaluated in 52 M. canis strains recently isolated from 14 human patients, 12 dogs, 15 symptomatic, and 11 asymptomatic cats. In addition, thermotolerance was assessed by comparative analysis of fungal growth at 25 °C and 35 °C. Keratinase activity was low in 34 and moderate in 18 strains. Aspartic-protease activity was low in 7, moderate in 33, and high in 12 strains. Hemolysin activity was low in 44 and moderate in 8 strains. All strains were classified as low producers of catalase. All but three strains produced urease in vitro, with a broad range of activity. The strains presented in vitro growth at the two studied temperatures were classified as presenting low (36.5%), medium (44.3%), or high (19.2%) thermotolerance. There was no statistically significant difference in the new putative virulence-associated factors studied among the different hosts, which suggests that they may have a similar role on human, cat, and dog infection. Also, no difference was observed between strains isolated from symptomatic and asymptomatic cats. This suggests that these factors have a limited impact on the fate of feline dermatophytosis caused by M. canis.

Keratin hydrolysis by dermatophytes

Dermatophytes are the most common cause of superficial fungal infections (tinea infections) and are a specialized group of filamentous fungi capable of infecting and degrading keratinised tissues, including skin, hair, and nail. Essential to their pathogenicity and virulence is the production of a broad spectrum of proteolytic enzymes and other key proteins involved in keratin biodegradation and utilization of its breakdown products. The initial stage of biodegradation of native keratin is considered to be sulfitolysis, in which the extensive disulfide bridges present in keratin are hydrolyzed, although some secreted subtilisins can degrade dye-impregnated keratin azure without prior reduction (Sub3 and Sub4). Sulfitolysis facilitates the extracellular biodegradation of keratin by the dermatophytes' extensive array of endo- and exoproteases. The importance of dermatophyte proteases in infection is widely recognized, and these enzymes have also been identified as important virulence determinants and allergens. Finally, the short peptide and amino acid breakdown products are taken up by the dermatophytes, using as yet poorly characterised transporters, and utilized for metabolism. In this review, we describe the process of keratin biodegradation by dermatophytes, with an especial focus on recent developments in cutting edge molecular biology and '-omic' studies that are helping to dissect the complex process of keratin breakdown and utilization.

Fungal infections in animals: a patchwork of different situations

The importance of fungal infections in both human and animals has increased over the last decades. This article represents an overview of the different categories of fungal infections that can be encountered in animals originating from environmental sources without transmission to humans. In addition, the endemic infections with indirect transmission from the environment, the zoophilic fungal pathogens with near-direct transmission, the zoonotic fungi that can be directly transmitted from animals to humans, mycotoxicoses and antifungal resistance in animals will also be discussed. Opportunistic mycoses are responsible for a wide range of diseases from localized infections to fatal disseminated diseases, such as aspergillosis, mucormycosis, candidiasis, cryptococcosis and infections caused by melanized fungi. The amphibian fungal disease chytridiomycosis and the Bat White-nose syndrome are due to obligatory fungal pathogens. Zoonotic agents are naturally transmitted from vertebrate animals to humans and vice versa. The list of zoonotic fungal agents is limited but some species, like Microsporum canis and Sporothrix brasiliensis from cats, have a strong public health impact. Mycotoxins are defined as the chemicals of fungal origin being toxic for warm-blooded vertebrates. Intoxications by aflatoxins and ochratoxins represent a threat for both human and animal health. Resistance to antifungals can occur in different animal species that receive these drugs, although the true epidemiology of resistance in animals is unknown, and options to treat infections caused by resistant infections are limited.

Exoproteome Analysis of Human Pathogenic Dermatophyte Species and Identification of Immunoreactive Proteins

PURPOSE

Increasing incidence of onychomycosis and tinea pedis in humans of industrialized countries together with deep tissue infections are a therapeutic challenge in clinical mycology. For a better understanding of the pathology and immunology of infection, the authors analyze the exoproteomes of three reference strains of the most common clinical dermatophyte species (Trichophyton rubrum, Trichophyton interdigitale, Arthroderma benhamiae) and of Trichophyton strains isolated from affected patients.

EXPERIMENTAL DESIGN

Extracellular proteins of those in vitro grown strains are separated via 2D High Performance Electrophoresis and identified by mass spectrometry to find proteins with provoked host immune reactivity.

RESULTS

More than 80 secreted proteins including virulence factors such as peptidases and other hydrolases are identified. By Western blotting with respective patient sera, up to 31 proteins with significant antigen-antibody reactions are detected in comparison with control sera, for example, peptidases as well as several oxidoreductases. One protein, beta-glucosidase F2SZI9 seems to be a commonly processed antigen in all Trichophyton infections.

CONCLUSIONS AND CLINICAL RELEVANCE

These first global exoproteome data of three dermatophyte species can be a stepping stone on the way to further study the molecular mechanisms of Trichophyton pathogenicity-associated traits. Possible candidates for potential new diagnostic methods or vaccination have to be validated in further investigations.

High-level expression, purification, and enzymatic characterization of a recombinant Aspergillus sojae alkaline protease in Pichia pastoris

An alkaline protease (Ap) was cloned from Aspergillus sojae GIM3.33 via RT-PCR technique. A truncated Ap without the signal peptide was successfully expressed in the Pichia pastoris KM71 strain. The following describes the optimal process conditions for the recombinant engineering of a strain expressing a recombinant Ap (rAp) in a triangular flask: inoculum concentration OD₆₀₀ value 20.0 in 40 mL working volume (in 500 mL flasks), methanol addition (1.0%; volume ratio), 0.02% biotin solution (60 μL), and YNB primary concentration (13.0 g/L). Under these conditions, the protease activity of rAp in the fermentation broth reached 400.4 ± 40.5 U/mL after induction for three days. The rAp was isolated and purified, and its enzymatic characteristics were tested. Its optimal pH was 10.0, and it remained stable in a pH range of 7.0-10.0. Its optimal temperature was 45 °C and it retained >50% activity at 40 °C for 60 min. The rAp activity was significantly inhibited by PMSF, Zn²⁺ and Fe²⁺ and the rAp had a broad substrate specificity for natural proteins and synthetic peptide substrates, and preferred substrates at P1 position with large hydrophobic side-chain groups. Compared to Papain (8.7%) and Alcalase (12.2%), the degree of hydrolysis of rAp to soy protein isolate was 16.5%; therefore, rAp was a good candidate for the processing of food industry byproducts.

Structural characterization, catalytic, kinetic and thermodynamic properties of Keratinase from Bacillus pumilus FH9

Bacillus pumilus FH9 keratinase was purified to homogeneity with a 59.9% yield through a series of three steps. The purified enzyme was a monomeric protein with a molecular mass around 50kDa and containing 7.3% carbohydrates. The pure B. pumilus FH9 keratinase was optimally active at pH 9.0 and 60°C. The calculated activation energy for keratin hydrolysis was 24.52kJmol^-1 and its temperature quotient (Q₁₀) was 1.19. The calculated values of thermodynamic parameters for keratin hydrolysis were as follows: ΔH*=21.75kJmol^-1, ΔG*=65.86kJmol^-1 ΔS*=-132.46Jmol^-1K^-1, (ΔG*_E-S)=4.74kJmol^-1 and ΔG*_E-T=-11.254kJmol^-1. The pure keratinase exhibited K_m, V_max, k_cat and k_cat/K_m of 5.55mg/ml keratin, 5882Umgprotein^-1 323.54s^-1 and 58.28 (s^-1/mgml^-1). The calculated half-life time at 50, 60, 70 and 80°C was 90.69, 59.1, 16.62 and 9.48min, respectively. Similarly, the thermodynamic parameters for irreversible thermal inactivation at temperature ranging from 50 to 80°C were determined. The pure enzyme was stimulated by Ca²⁺ and Mg²⁺. However, Zn²⁺, EDTA, Co²⁺ and Hg²⁺ significantly inhibited the enzyme activity. The purified enzyme was able to hydrolyze different substrates showing its higher proteolytic activity on casein, bovine serum albumin, and collagen, followed by feather, horn and wool.

A novel organic solvent- and detergent-stable serine alkaline protease from Trametes cingulata strain CTM10101

A protease-producing fungus was isolated from an alkaline wastewater of chemical industries and identified as Trametes cingulata strain CTM10101 on the basis of the ITS rDNA gene-sequencing. It was observed that the fungus strongly produce extracellular protease grown at 30°C in potato-dextrose-broth (PDB) optimized media (13500U/ml). The pure serine protease isolated by Trametes cingulata (designated SPTC) was purified by ammonium sulfate precipitation-dialysis followed by heat-treatment and UNO S-1 FPLC cation-exchange chromatography. The chemical characterization carried on include phisico-chemical determination and spectroscopie analysis. The MALDI-TOF/MS analysis revealed that the purified enzyme was a monomer with a molecular mass of 31405.16-Da. The enzyme had an NH2-terminal sequence of ALTTQTEAPWALGTVSHKGQAST, thus sharing high homology with those of fungal-proteases. The optimum pH and temperature values of its proteolytic activity were pH 9 and 60°C, respectively, and its half-life times at 60 and 70°C were 9 and 5-h, respectively. It was completely inhibited by PMSF and DFP, which strongly suggested its belonging to the serine protease family. Compared to Flavourzyme(®)500L from Aspergillus oryzae and Thermolysin typeX from Geobacillus stearothermophilus, SPTC displayed higher levels of hydrolysis, substrate specificity, and catalytic efficiency as well as elevated organic solvent tolerance and considerable detergent stability. Finally, SPTC could potentially be used in peptide synthesis and detergent formulations.

Genetic variability in Microsporum canis isolated from cats, dogs and humans in Brazil

Dermatophytosis caused by Microsporum canis is a heterogeneous disease with variable clinical manifestations. M. canis is a zoophilic dermatophyte and the most frequent fungi isolated from dogs, cats and children in Brazil. The aim of this study was to investigate the genetic variability of M. canis isolates from different animal species using two microsatellite markers, namely, McGT(13) and McGT(17), and to correlate the results with the clinical and epidemiological patient data in Brazil. The study included a global set of 102 M. canis strains, including 37 symptomatic cats, 35 asymptomatic cats, 19 human patients with tinea, 9 asymptomatic dogs and 2 symptomatic dogs. A total of 14 genotypes were identified, and 6 large populations were distinguished. There was no correlation between these multilocus genotypes and the clinical and epidemiological data, including the source, symptomatology, clinical picture, breed, age, sex, living conditions and geographic location. These results demonstrate that the use of microsatellite polymorphisms is a reliable method for the differentiation of M. canis strains. However, we were unable to demonstrate a shared clinical and epidemiological pattern among the same genotype samples.

Keratin degradation by dermatophytes relies on cysteine dioxygenase and a sulfite efflux pump

Millions of people suffer from superficial infections caused by dermatophytes. Intriguingly, these filamentous fungi exclusively infect keratin-rich host structures such as hair, nails, and skin. Keratin is a hard, compact protein, and its utilization by dermatophytes for growth has long been discussed as a major virulence attribute. Here, we provide strong support for the hypothesis that keratin degradation is facilitated by the secretion of the reducing agent sulfite, which can cleave keratin-stabilizing cystine bonds. We discovered that sulfite is produced by dermatophytes from environmental cysteine, which at elevated concentrations is toxic for microbes and humans. We found that sulfite formation from cysteine relies on the key enzyme cysteine dioxygenase Cdo1. Sulfite secretion is supported by the sulfite efflux pump Ssu1. Targeted mutagenesis proved that dermatophyte mutants in either Cdo1 or Ssu1 were highly growth-sensitive to cysteine, and mutants in Ssu1 were specifically sensitive to sulfite. Most notably, dermatophyte mutants in Cdo1 and Ssu1 were specifically growth-defective on hair and nails. As keratin is rich in cysteine, our identified mechanism of cysteine conversion and sulfite efflux supports both cysteine and sulfite tolerance per se and progression of keratin degradation. These in vitro findings have implications for dermatophyte infection pathogenesis.

Difference in keratinase activity of dermatophytes at different environmental conditions is an attribute of adaptation to parasitism

Dermatophytes are a group of morphologically and physiologically related moulds, which cause well-defined infection called dermatophytosis. The enzymatic ability of fungi to decompose keratin has long been interpreted as a key innovation in the evolution of animal dermatology. In the present study, keratinase activity profile among Trichophyton mentagrophytes, Trichophyton rubrum, Microsporum canis and Microsporum gypseum isolated on keratin substrates such as human hair, human nail and chicken feather at variable environmental conditions of temperature, pH and metal ions was elucidated. All the above-mentioned fungal strains were isolated from soil using To-KA-Va baiting technique and keratinolytic activity was measured spectrophotometrically. In the temperature range of 30-40 °C and slightly alkaline pH (7.0-8.0), Trichophyton produced the highest activity of keratinase. It can be presumed that high enzyme production of Trichophyton species at normal body temperature range and pH could be an attribute for obligate anthropization in some dermatophytes.

Dermatophyte virulence factors: identifying and analyzing genes that may contribute to chronic or acute skin infections

Dermatophytes are prevalent causes of cutaneous mycoses and, unlike many other fungal pathogens, are able to cause disease in immunocompetent individuals. They infect keratinized tissue such as skin, hair, and nails, resulting in tinea infections, including ringworm. Little is known about the molecular mechanisms that underlie the ability of these organisms to establish and maintain infection. The recent availability of genome sequence information and improved genetic manipulation have enabled researchers to begin to identify and study the role of virulence factors of dermatophytes. This paper will summarize our current understanding of dermatophyte virulence factors and discuss future directions for identifying and testing virulence factors.

Keratinolytic activity of purified alkaline keratinase produced by Scopulariopsis brevicaulis (Sacc.) and its amino acids profile

Sodium dodecyl sulfate-polyacrlyamide gel electrophoresis (SDS-PAGE) was used to assess the purity and molecular weight of the previously purified alkaline keratinase enzyme of Scopulariopsis brevicaulis. The enzyme was homogenous, as seen by a single band of protein, and had an apparent molecular weight of 28.5 kDa. Amino acid profile of the purified keratinase revealed that it was composed of 14 different amino acids with high proportions of glutamic acid (20.86%), alanine (14.52%), glycine (14.21%), leucine (8.59%) and serine (7.81%). The enzyme contained moderate amounts of valine (6.01%), threonine (5.58%) and phenyl alanine (5.22%). The purified enzyme of S. brevicaulis exerted a potent keratinolytic activity and was capable to hydrolyze different keratinaceous materials with highest activity on chicken feathers followed by human nails and human hair.

Fungal proteases and their pathophysiological effects

Proteolytic enzymes play an important role in fungal physiology and development. External digestion of protein substrates by secreted proteases is required for survival and growth of both saprophytic and pathogenic species. Extracellular serine, aspartic, and metalloproteases are considered virulence factors of many pathogenic species. New findings focus on novel membrane-associated proteases such as yapsins and ADAMs and their role in pathology. Proteases from fungi induce inflammatory responses by altering the permeability of epithelial barrier and by induction of proinflammatory cytokines through protease-activated receptors. Many fungal allergens possess proteolytic activity that appears to be essential in eliciting Th2 responses. Allergenic fungal proteases can act as adjuvants, potentiating responses to other allergens. Proteolytic enzymes from fungi contribute to inflammation through interactions with the kinin system as well as the coagulation and fibrinolytic cascades. Their effect on the host protease-antiprotease balance results from activation of endogenous proteases and degradation of protease inhibitors. Recent studies of the role of fungi in human health point to the growing importance of proteases not only as pathogenic agents in fungal infections but also in asthma, allergy, and damp building related illnesses. Proteolytic enzymes from fungi are widely used in biotechnology, mainly in food, leather, and detergent industries, in ecological bioremediation processes and to produce therapeutic peptides. The involvement of fungal proteases in diverse pathological mechanisms makes them potential targets of therapeutic intervention and candidates for biomarkers of disease and exposure.

Extracellular protease expression in Microsporum gypseum complex, its regulation and keratinolytic potential

Two soil isolates of Microsporum gypseum were studied for the production of extracellular proteases. Both the strains secreted protease on glucose-gelatin medium. The enzyme activity peaked on day 15 at 28 °C. Asparagine repressed protease yield. Sugars caused catabolite repression of protease formation. Protease activities of both the isolates were significantly affected by incubation period, culture media and carbohydrates used. Both the strains grew on the skin bait and caused a gravimetrically measurable loss of the substrate. Despite less pronounced differences in the keratinase levels, great variations occurred in the amount of keratin degraded by two isolates. Keratinase production as well as loss in substrate mass was better in glucose-lacking flasks than those containing the sugar. Although the rate of keratin degradation was independent of enzyme production, statistically positive correlations were recorded between loss in substrate mass: yielded dry mycelial weight and substrate degradation: keratinase levels.

Secretion of an endogenous subtilisin by Pichia pastoris strains GS115 and KM71

The methylotrophic yeast Pichia pastoris is widely used for the expression of heterologous enzymes. While the purity of the desired expression product is of major importance for many applications, we found that recombinant enzymes produced in methanol medium were contaminated by a 37-kDa endogenous yeast protease. This enzyme was completely inhibited by phenylmethanesulfonyl fluoride (PMSF) but not by 1,10-phenanthroline, EDTA, and pepstatin A, suggesting the nature of a serine protease. Its secretion was abolished in P. pastoris strains GS115 and KM71 by specific mutagenesis of a subtilisin gene (SUB2) but not by inactivation of the gene encoding vacuolar proteinase B (PRB). Bioinformatic comparisons of Sub2 protein with subtilisins from other fungal genomes and phylogenetic analyses indicated that this enzyme is not an orthologue of the vacuolar protease cerevisin generally present in yeasts but is more closely related to another putative subtilisin found in a small number of yeast genomes. During growth of P. pastoris, Sub2 was produced as a secreted enzyme at a concentration of 10 microg/ml of culture supernatant after overexpression of the full-length SUB2 gene. During fermentative production of recombinant enzymes in methanol medium, 1 ml of P. pastoris culture supernatant was found to contain approximately 3 ng of Sub2, while the enzyme was not detected during growth in a medium containing glycerol as a carbon source. The mutant strain GS115-sub2 was subsequently used as a host for the production of recombinant proteases without endogenous subtilisin contamination.

Cloning, expression and characterization of the serine protease gene from Chaetomium thermophilum

AIMS

Microbial proteases play an essential role in scientific research and commercial applications. This study is to clone, sequence, and express a thermostable protease gene from the thermophilic fungi Chaetomium thermophilum and to generate yeast strains expressing C. thermophilum protease suitable for industrial applications.

METHODS AND RESULTS

Degenerate primers were designed based on the conserved domain of other identified serine proteases and cDNA fragment of C. thermophilum gene pro was obtained through reverse transcriptase-polymerase chain reaction (RT-PCR). The full-length cDNA of 2007 bp was generated using RACE amplification. The cDNA contains an open reading frame of 1596 bp encoding 532 amino acids. Sequence analysis of the deduced amino acid sequence revealed high homology with the catalytic domains of the subtilisin serine proteases. The C. thermophilum gene pro was expressed in Escherichia coli BL21 (DE3) and Pichia pastoris, respectively and soluble protein was obtained in P. pastoris. The expressed protease was secreted into the culture medium by the yeast in a functional active form and the purified recombinant protease exhibits optimum catalytic activity at pH 8.0 and 60 degrees C. The enzyme is stable at 60 degrees C. The integration of gene pro into P. pastoris genome is stable after 10 generations and the yeast transformants showed a consistent protease expression.

CONCLUSIONS

Gene pro encoding a serine protease from C. thermophilum was cloned, sequenced, and overexpressed successfully in P. pastoris. The expressed protease was purified and the properties of the recombinant protease are characterized.

SIGNIFICANCE AND IMPACT OF THE STUDY

Chaetomium thermophilum is a soil-borne thermophilic fungus and the protease cloned from it is stable in a high temperature and a wide rage of pH. The overexpression of the enzyme in a mesophilic micro-organism offers a potential value for scientific research and commercial applications.

Comparative analysis of secreted enzymes between the anthropophilic-zoophilic sister species Trichophyton tonsurans and Trichophyton equinum

Trichophyton tonsurans (TT) and Trichophyton equinum (TE) are two closely related dermatophytes with very different host preferences. This study was designed to examine the genetic and transcript level variations of secreted enzymes between TT and TE. Thirty-one genes representing 10 gene families were selected for comparison and complete genomic and cDNA sequences were elucidated. Sequence analyses of the selected genes identified 104 polymorphisms between the two dermatophytes, 37 of which are expected to encode changes in their polypeptide sequence. Quantitative RT-PCR was used to examine the differences in levels of transcript between TT and TE grown over 14d in aqueous keratin medium. Differences in transcript expression between TT and TE were gene specific and ranged from 1.1-fold to 33-fold. Intra-specific variability across all genes ranged from 41% to 250%. Despite their overall genetic similarity, TT and TE exhibit a moderate degree of variability in the genomic make-up of their secreted enzymes and the extent to which they are transcribed when grown in an aqueous keratin medium. Such differences may contribute to how these genetically similar organisms have adapted to infect divergent host organisms.

Agrobacterium tumefaciens-mediated transformation of the dermatophyte, Trichophyton mentagrophytes: an efficient tool for gene transfer

Agrobacterium tumefaciens-mediated transformation (ATMT) was used to facilitate gene transfer into the clinically important dermatophyte, Trichophyton mentagrophytes (teleomorph: Arthroderma vanbreuseghemii). A binary vector containing a hygromycin B resistance cassette was introduced into A. tumefaciens, and the resultant strain was co-cultivated with fungal small conidia. Transformation yielded a large number of hygromycin B-resistant transformants. Hybridization analysis showed that most of the transformants harboured a single copy of T-DNA randomly integrated into the genome. Transformation frequency was increased to more than 200 per 10(7) conidia by optimizing the co-cultivation time and temperature. ATMT was then used for targeted gene disruption mediated by homologous recombination. Using a PCR-based strategy, we isolated the areA/nit-2-like nitrogen regulatory gene (tnr:Trichophytonnitrogen regulator) from T. mentagrophytes. A binary vector containing two regions of the tnr locus flanking the hygromycin B resistance cassette was constructed and introduced into T. mentagrophytesvia ATMT. Transformants with disruption of the areA/nit-2-like gene (tnr) were obtained in three of four independent disruption experiments, most of which showed homologous recombination via double crossover without additional ectopic integration of the disruption construct.

Development of transformation system for Trichophyton rubrum by electroporation of germinated conidia

Dermatophytes are the fungi that can cause infections of skin, hair, and nails due to their ability to utilize keratin. The genetic transformation systems of dermatophytes were successfully applied to Trichophyton mentagrophytes and Microsporum canis. Here we describe the procedure for genetic transformation of Trichophyton rubrum by electroporation of their germinated conidia. A linearized transformation vector (pCHSH75-Pch/GFP/TtrpC) containing bacterial hygromycin B phosphotransferase gene (hph) and green fluorescent protein gene (egfp) was introduced into the germinated conidia of T. rubrum by electroporation. PCR reaction analysis showed that egfp gene was integrated randomly and Southern blotting analysis demonstrated a single integration of hph gene into the chromosomal DNA of randomly selected transformant. In this work we report the efficient transformation and selection of the stable T. rubrum transformants.

Secreted dipeptidyl peptidases as potential virulence factors for Microsporum canis

Dermatophytoses caused by Microsporum canis are frequently encountered in cats and dogs; they are highly contagious and readily transmissible to humans. In this study, two single genes, respectively coding for dipeptidyl peptidases IV and V (DppIV and DppV), were isolated and characterized. Both proteins share homology with serine proteases of the S9 family, some of which display properties compatible with implication in pathogenic processes. Both genes are expressed in vivo in experimentally infected guinea-pigs and in naturally infected cats, and when the fungus is grown on extracellular matrix proteins as the sole nitrogen and carbon source. DppIV and V were produced as active recombinant proteases in the yeast Pichia pastoris; the apparent molecular weight of rDppV is 83 kDa, whereas rDppIV appears as a doublet of 95 and 98 kDa. Like other members of its enzymatic subfamily, rDppIV has an unusual ability to cleave Pro-X bonds. This activity does not enhance the solubilization of keratin by fungal secreted endoproteases, and the protease probably acts solely on small soluble peptides. RDppV showed no ability to induce delayed-type hypersensitivity (DTH) skin reactions in guinea-pigs, despite the known immunogenic properties of homologous proteins.

Secreted subtilisins of Microsporum canis are involved in adherence of arthroconidia to feline corneocytes

Microsporum canis is a pathogenic fungus that causes a superficial cutaneous infection called dermatophytosis, mainly in cats and humans. The mechanisms involved in adherence of M. canis to epidermis have never been investigated. Here, a model was developed to study the adherence of M. canis to feline corneocytes through the use of a reconstructed interfollicular feline epidermis (RFE). In this model, adherence of arthroconidia to RFE was found to be time-dependent, starting at 2 h post-inoculation and still increasing at 6 h. Chymostatin, a serine protease inhibitor, inhibited M. canis adherence to RFE by 53%. Moreover, two mAbs against the keratinolytic protease subtilisin 3 (Sub3) inhibited M. canis adherence to RFE by 23%, suggesting that subtilisins, and Sub3 in particular, are involved in the adherence process.

Pathogenesis of dermatophytosis

Despite the superficial localization of most dermatophytosis, host-fungus relationship in these infections is complex and still poorly elucidated. Though many efforts have been accomplished to characterize secreted dermatophytic proteases at the molecular level, only punctual insights have been afforded into other aspects of the pathogenesis of dermatophytosis, such as fungal adhesion, regulation of gene expression during the infection process, and immunomodulation by fungal factors. However, new genetic tools were recently developed, allowing a more rapid and high-throughput functional investigation of dermatophyte genes and the identification of new putative virulence factors. In addition, sophisticated in vitro infection models are now used and will open the way to a more comprehensive view of the interactions between these fungi and host epidermal cells, especially keratinocytes.

Secreted proteases from dermatophytes

Dermatophytes are highly specialized pathogenic fungi that exclusively infect the stratum corneum, nails or hair, and it is evident that secreted proteolytic activity is important for their virulence. Endo- and exoproteases-secreted by dermatophytes are similar to those of species of the genus Aspergillus. However, in contrast to Aspergillus spp., dermatophyte-secreted endoproteases are multiple and are members of two large protein families, the subtilisins (serine proteases) and the fungalysins (metalloproteases). In addition, dermatophytes excrete sulphite as a reducing agent. In the presence of sulphite, disulphide bounds of the keratin substrate are directly cleaved to cysteine and S-sulphocysteine, and reduced proteins become accessible for further digestion by various endo- and exoproteases secreted by the fungi. Sulphitolysis is likely to be an essential step in the digestion of compact keratinized tissues which precedes the action of all proteases.

Reconstructed interfollicular feline epidermis as a model for Microsporum canis dermatophytosis

Microsporum canis is a pathogenic fungus that causes a superficial cutaneous infection called dermatophytosis. The complexity of mechanisms involved in dermatophytic infections makes relevant in vivo studies particularly difficult to perform. The aim of this study was to develop a new in vitro model of M. canis dermatophytosis using feline fetal keratinocytes in reconstructed interfollicular epidermis, and to investigate its relevance in studying the host-pathogen relationship. Histological analysis of reconstructed interfollicular feline epidermis (RFE) revealed a fully differentiated epidermis. A proliferation assay showed replicating cells only in the basal layer, indicating that RFE is a well-stratified living tissue, leading to the formation of a horny layer. Histopathological analysis of RFE infected by M. canis arthroconidia revealed that the fungus invades the stratum corneum and produces SUB3, a keratinase implicated in the infectious process. In view of these results, an M. canis dermatophytosis model on RFE seems to be a useful tool to investigate mechanisms involved in natural M. canis feline infections.

Actividad proteolítica extracelular y análisis molecular de cepas de Microsporum canis aisladas de gatos con y sin sintomatología

Microsporum canis is the main zoophylic dermatophyte in dogs and cats, and it is also an important zoonotic agent. The literature showed that cats are asymptomatic carriers of M. canis. This is apparently due to host resistance and/or the presence of strains with lower virulence. This study was aimed to evaluate the keratinolytic, elastinolytic and collagenolytic activities of M. canis strains and their relationship with symptomatic and asymptomatic cats. In addition, these strains were analysed by RFLP. The strains isolated from cats with clinical dermatophytosis had higher keratinase and elastase activity than those isolated from asymptomatic animals (p minus than 0.05). There were not differences in RFLP patterns based on Hind III digestion.

Screening for a new Streptomyces strain capable of efficient keratin degradation

Keratinous wastes could be degraded by some microorganisms in nature. Native human foot skin (NHFS) was used as sole nitrogen source to screen microorganisms with keratin-degrading capability. From approximately 200 strains, a strain of Streptomyces sp. strain No.16 was found to possess the strongest keratinolytic activity, and the total activity in the culture was 110 KU/ml with specific activity of 2870 KU/mg protein (KU: keratinase unit). Substrate specificity test indicated that the crude keratinase could degrade keratin azure, human hair, cock feathers and collagen. The optimal pH of the crude keratinase ranged from 7.5 to 10 and the temperature ranged from 40 degrees C to 55 degrees C. Metal chelating agent ethylenediamine tetraacetic acid obviously stimulated the keratinolytic activity but suppressed the proteolytic activity. To our knowledge, this is the first report on specific induction of keratinases by NHFS from an actinomycete. Moreover, excellent characteristics of its crude keratinase may lead to the potential application in waste treatment and recovery, poultry and leather industry, medicine, and cosmetic development.

Analysis of the dermatophyte Trichophyton rubrum expressed sequence tags

Background

Dermatophytes are the primary causative agent of dermatophytoses, a disease that affects billions of individuals worldwide. Trichophyton rubrum is the most common of the superficial fungi. Although T. rubrum is a recognized pathogen for humans, little is known about how its transcriptional pattern is related to development of the fungus and establishment of disease. It is therefore necessary to identify genes whose expression is relevant to growth, metabolism and virulence of T. rubrum.

Results

We generated 10 cDNA libraries covering nearly the entire growth phase and used them to isolate 11,085 unique expressed sequence tags (ESTs), including 3,816 contigs and 7,269 singletons. Comparisons with the GenBank non-redundant (NR) protein database revealed putative functions or matched homologs from other organisms for 7,764 (70%) of the ESTs. The remaining 3,321 (30%) of ESTs were only weakly similar or not similar to known sequences, suggesting that these ESTs represent novel genes.

Conclusion

The present data provide a comprehensive view of fungal physiological processes including metabolism, sexual and asexual growth cycles, signal transduction and pathogenic mechanisms.

Isolation, characterization, and disruption of dnr1, the areA/nit-2-like nitrogen regulatory gene of the zoophilic dermatophyte, Microsporum canis

A homolog of the major nitrogen regulatory genes areA from Aspergillus nidulans and nit-2 from Neurospora crassa was isolated from the zoophilic dermatophyte, Microsporum canis. This gene, dnr1, encodes a polypeptide of 761 amino acid residues containing a single zinc-finger DNA-binding domain, which is almost identical in amino acid sequence to the zinc-finger domains of AREA and NIT-2. The functional equivalence of dnr1 to areA was demonstrated by complementation of an areA loss-of-function mutant of A. nidulans with dnr1 cDNA. To further characterize this gene, dnr1 was disrupted by gene replacement based on homologous recombination. Of 100 transformants analyzed, two showed the results expected for replacement of dnr1. The growth properties of the two dnr1(-) mutant strains on various nitrogen sources were examined. Unlike the A. nidulansareA(-) mutant, these dnr1(-) mutants showed significantly reduced growth on ammonia, a preferred nitrogen source for fungi. These mutant strains were also able to utilize various amino acids for growth. In comparison with wild-type M. canis, the two dnr1(-) mutants showed reduced growth on medium containing keratin as the sole nitrogen source. This is the first report describing successful production of targeted gene-disrupted mutants by homologous recombination and their phenotypic analysis in dermatophytes.

Partial purification and characterization of a 37 kDa extracellular proteinase from Trichophyton vanbreuseghemii

An exocellular proteinase synthesized by the geophilic dermatophyte Trichophyton vanbreuseghemii has been purified and characterized. The fungus obtained from soil in Iran was cultivated in modified Czapek-Dox liquid medium containing 0.1% bacteriological peptone and 1% glucose as the nitrogen and carbon sources. Partial purification of the proteinase was accomplished by (NH(4))(2)SO(4) precipitation, followed by ion exchange chromatography. Analysis of the enzyme by SDS-PAGE revealed a single polypeptide chain with an apparent molecular mass of 37 kDa. Proteinase activity was optimum at pH 8, but remained high in the range of pH 7-11. Moreover, the partially purified enzyme presented a keratinolytic activity as evidenced by the keratin azure test. The inhibition profile and the good activity of the enzyme towards the synthetic substrate N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide suggested that it belonged to the chymotrypsin/subtilisin group of serine proteinases. The keratinolytic properties of T. vanbreuseghemii suggest that this fungus may be an alternative for the recycling of industrial keratinic wastes.

Reproducible genetic transformation system for two dermatophytes, Microsporum canis and Trichophyton mentagrophytes

A reproducible genetic transformation system was developed for two major dermatophytes, Microsporum canis and Trichophyton mentagrophytes. Two circular transformation vectors carrying either the bacterial hygromycin B phosphotransferase gene (hph) or both the hph and green fluorescent protein (eGFP) genes under the control of a promoter sequence from Cochlibolus heterostrophus were introduced independently into the protoplasts by a polyethylene glycol (PEG)-mediated method. Polymerase chain reaction (PCR) showed that the hph gene was integrated randomly into the chromosomal DNA of the transformants through non-homologous recombination. Southern blotting analysis also demonstrated a single or multiple integration of the hph gene into the chromosomal DNA. Fluorescence due to eGFP gene expression was observed in the T. mentagrophytes transformants, and the transformants retained mitotic stability through subculture. This reproducible transformation system provides a method for the genetic manipulation of these pathogens, which will facilitate detailed molecular analysis of dermatophytosis.

Similarities and specificities of fungal keratinolytic proteases: comparison of keratinases of Paecilomyces marquandii and Doratomyces microsporus to some known proteases

Based on previous screening for keratinolytic nonpathogenic fungi, Paecilomyces marquandii and Doratomyces microsporus were selected for production of potent keratinases. The enzymes were purified and their main biochemical characteristics were determined (molecular masses, optimal temperature and pH for keratinolytic activity, N-terminal amino acid sequences). Studies of substrate specificity revealed that skin constituents, such as the stratum corneum, and appendages such as nail but not hair, feather, and wool were efficiently hydrolyzed by the P. marquandii keratinase and about 40% less by the D. microsporus keratinase. Hydrolysis of keratin could be increased by the presence of reducing agents. The catalytic properties of the keratinases were studied and compared to those of some known commercial proteases. The profile of the oxidized insulin B-chain digestion revealed that both keratinases, like proteinase K but not subtilisin, trypsin, or elastase, possess broad cleavage specificity with a preference for aromatic and nonpolar amino acid residues at the P-1 position. Kinetic studies were performed on a synthetic substrate, succinyl-Ala-Ala-Pro-Phe-p-nitroanilide. The keratinase of P. marquandii exhibited the lowest Km among microbial keratinases reported in the literature, and its catalytic efficiency was high in comparison to that of D. microsporus keratinase and proteinase K. All three keratinolytic enzymes, the keratinases of P. marquandii and D. microsporus as well as proteinase K, were significantly more active on keratin than subtilisin, trypsin, elastase, chymotrypsin, or collagenase.