Candida guilliermondii isolated from HIV-infected human secretes a 50 kDa serine proteinase that cleaves a broad spectrum of proteinaceous substrates

In silico structural exploration of serine protease from a CTG-clade yeast Meyerozyma guilliermondii strain SO

In eukaryotes, serine proteases are cellular localized hydrolases reported to regulate essential biological reactions. Improved industrial applications of proteins are aided by prediction and analysis of their 3-dimensional structures (3D). A serine protease was identified from CTG-clade yeast Meyerozyma guilliermondii strain SO and its 3D structure as well as its catalytic attributes have not been fully understood yet, thus we seek to report on the catalytic mechanism of M. guilliermondii strain SO MgPRB1 using substrate PMSF via in silico docking as well as its stability by way of disulfide bonds formation. Herein, bioinformatics tools and techniques were used to predict, validate and analyze the possible changes of CUG ambiguity (if any) in strain SO using template PDB ID: 3F7O. Structural assessments confirmed the classic catalytic triad Asp305, His337, and Ser499. Superimposition of MgPRB1 and template 3F7O structures revealed the unlinked cysteine residues between Cys341, Cys440, Cys471 and Cys506 of MgPRB1 compared to template 3F7O with two disulfide bonds formation, which confers structural stability. In conclusion, serine protease structure from strain SO was successfully predicted and studies towards understanding at the molecular level may be undertaken for its potential applications in the degradation of peptide bonds.

In silico identification of prospective virulence factors associated with candidiasis in Meyerozyma guilliermondii strain SO from genome dataset

Background

Meyerozyma guilliermondii is a prospective yeast that has extensively contributed to the biotechnology sector. In 2015, M. guilliermondii strain SO which was isolated from spoiled orange has successfully been developed as an inducer-free expression system and attained a significant impact in producing industrially important recombinant proteins. The species possesses high similarity to Candida albicans which may cause candidiasis. The industrial-benefiting M. guilliermondii strain SO has been underexplored for its virulence status. Thus, this study aimed to document the potential virulence factors through the comprehensive in silico analysis of M. guilliermondii strain SO genome. This analysis demonstrated the molecular characterization which could distinguish the pathogenicity status of M. guilliermondii.

Results

The genome data were generated from Illumina HiSeq 4000 sequencing platform and assembled into 51 scaffolds successfully accumulating a genome size of 10.63 Mbp. These enclosed 5,335 CDS genes and 5,349 protein sequences with 43.72% GC content. About 99.29% of them were annotated to public databases. Komagataella phaffii, Saccharomyces cerevisiae and the reference strain of M. guilliermondii (ATCC 6260) were used as the controls. They were compared with our in-house strain SO to identify the consensus domain or subdomain which could putatively be considered as virulence factors. Candida albicans was used as the pathogenic model. Hence, hidden Markov model against strain SO proteome had identified secreted aspartic proteases (SAP), phospholipase C (PLC) and phospholipase D (PLD) with an E-value of 2.4e−107, 9.5e−200 and 0.0e+00, respectively, in resemblance of C. albicans. The topology of the phylogenetic analysis indicated that these virulence factors in M. guilliermondii strain SO and C. albicans branched from the same node and clustered together as a clade, signifying their molecular relatedness and congeneric among these species, subsequently proposing the virulence status of M. guilliermondii.

Conclusion

The SAP, PLC and PLD genes’ features that were significant in expressing determinants of pathogenicity were successfully identified in M. guilliermondii strain SO genome dataset, thus concluding the virulency of this species. On account of this finding, the strategy of gene knockout through CRISPR-Cas9 or homologous recombination strategies is needed to engineer the feasible novel expression host system. Over and above, the genetically modified strain of M. guilliermondii allegedly may eradicate the risk of candidiasis infection.

The Threat Called Candida haemulonii Species Complex in Rio de Janeiro State, Brazil: Focus on Antifungal Resistance and Virulence Attributes

Although considered rare, the emergent Candida haemulonii species complex, formed by C. haemulonii sensu stricto (Ch), C. duobushaemulonii (Cd) and C. haemulonii var. vulnera (Chv), is highlighted due to its profile of increased resistance to the available antifungal drugs. In the present work, 25 clinical isolates, recovered from human infections during 2011–2020 and biochemically identified by automated system as C. haemulonii, were initially assessed by molecular methods (amplification and sequencing of ITS1-5.8S-ITS2 gene) for precise species identification. Subsequently, the antifungal susceptibility of planktonic cells, biofilm formation and susceptibility of biofilms to antifungal drugs and the secretion of key molecules, such as hydrolytic enzymes, hemolysins and siderophores, were evaluated by classical methodologies. Our results revealed that 7 (28%) isolates were molecularly identified as Ch, 7 (28%) as Chv and 11 (44%) as Cd. Sixteen (64%) fungal isolates were recovered from blood. Regarding the antifungal susceptibility test, the planktonic cells were resistant to (i) fluconazole (100% of Ch and Chv, and 72.7% of Cd isolates), itraconazole and voriconazole (85.7% of Ch and Chv, and 72.7% of Cd isolates); (ii) no breakpoints were defined for posaconazole, but high MICs were observed for 85.7% of Ch and Chv, and 72.7% of Cd isolates; (iii) all isolates were resistant to amphotericin B; and (iv) all isolates were susceptible to echinocandins (except for one isolate of Cd) and to flucytosine (except for two isolates of Cd). Biofilm is a well-known virulence and resistant structure in Candida species, including the C. haemulonii complex. Herein, we showed that all isolates were able to form viable biofilms over a polystyrene surface. Moreover, the mature biofilms formed by the C. haemulonii species complex presented a higher antifungal-resistant profile than their planktonic counterparts. Secreted molecules associated with virulence were also detected in our fungal collection: 100% of the isolates yielded aspartic proteases, hemolysins and siderophores as well as phospholipase (92%), esterase (80%), phytase (80%), and caseinase (76%) activities. Our results reinforce the multidrug resistance profile of the C. haemulonii species complex, including Brazilian clinical isolates, as well as their ability to produce important virulence attributes such as biofilms and different classes of hydrolytic enzymes, hemolysins and siderophores, which typically present a strain-dependent profile.

The serine peptidase inhibitor TPCK induces several morphophysiological changes in the opportunistic fungal pathogen Candida parapsilosis sensu stricto

Candida parapsilosis sensu stricto (C. parapsilosis) has emerged as the second/third commonest Candida species isolated from hospitals worldwide. Candida spp. possess numerous virulence attributes, including peptidases that play multiple roles in both physiological and pathological events. So, fungal peptidases are valid targets for new drugs development. With this premise in mind, we have evaluated the effect of serine peptidase inhibitors (SPIs) on both cell biology and virulence aspects of C. parapsilosis. First, five different SPIs, phenylmethylsulfonyl fluoride, benzamidine, 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride, N-α-tosyl-L-lysine chloromethyl ketone hydrochloride, and N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) were tested, and TPCK showed the best efficacy to arrest fungal growth. Subsequently, the ability of TPCK to modulate physiopathological processes was investigated. Overall, TPCK was able to (i) inhibit the cell-associated serine peptidase activities, (ii) promote morphometric and ultrastructural alterations, (iii) induce an increase in the intracellular oxidation level, which culminates in a vigorous lipid peroxidation and accumulation of neutral lipids in cytoplasmic inclusions, (iv) modulate the expression/exposition of surface structures, such as mannose/glucose-rich glycoconjugates, N-acetylglucosamine-containing molecules, chitin, polypeptides and surface aspartic peptidases, (v) reduce the adhesion to either polystyrene or glass surfaces as well as to partially disarticulate the mature biofilm, (vi) block the fungal interaction with macrophages, and (vii) protect Galleria mellonella from fungal infection, enhancing larvae survivability. Altogether, these results demonstrated that TPCK induced several changes over fungal biology besides the interference with aspects associated to C. parapsilosis virulence and pathogenesis, which indicates that SPIs could be novel promising therapeutic agents in dealing with candidiasis.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

Protease expression by microorganisms and its relevance to crucial physiological/pathological events

The treatment of infections caused by fungi and trypanosomatids is difficult due to the eukaryotic nature of these microbial cells, which are similar in several biochemical and genetic aspects to host cells. Aggravating this scenario, very few antifungal and anti-trypanosomatidal agents are in clinical use and, therefore, therapy is limited by drug safety considerations and their narrow spectrum of activity, efficacy and resistance. The search for new bioactive agents against fungi and trypanosomatids has been expanded because progress in biochemistry and molecular biology has led to a better understanding of important and essential pathways in these microorganisms including nutrition, growth, proliferation, signaling, differentiation and death. In this context, proteolytic enzymes produced by these eukaryotic microorganisms are appointed and, in some cases, proven to be excellent targets for searching novel natural and/or synthetic pharmacological compounds, in order to cure or prevent invasive fungal/trypanosomatid diseases. With this task in mind, our research group and others have focused on aspartic-type proteases, since the activity of this class of hydrolytic enzymes is directly implicated in several facets of basic biological processes of both fungal and trypanosomatid cells as well as due to the participation in numerous events of interaction between these microorganisms and host structures. In the present paper, a concise revision of the beneficial effects of aspartic protease inhibitors, with emphasis on the aspartic protease inhibitors used in the anti-human immunodeficiency virus therapy, will be presented and discussed using our experience with the following microbial models: the yeast Candida albicans, the filamentous fungus Fonsecaea pedrosoi and the protozoan trypanosomatid Leishmania amazonensis.

Identification of a Candida parapsilosis strain producing extracellular serine peptidase with keratinolytic activity

A yeast strain isolated from feather waste from a chicken processing plant was identified as Candida parapsilosis by biochemical tests and morphological studies. The yeast was able to grow in phosphate-buffered saline supplemented with 1% native feather as the sole carbon and nitrogen source. A keratin substrate was obtained from the feathers by dimethylsulphoxide extraction. A 20-fold concentrated culture supernatant from Candida parapsilosis grown on feathers was analysed by SDS-PAGE electrophoresis containing either 1% gelatin or 1% keratin as copolymerised substrates. The presence of a single band with an approximate molecular mass of 60 kDa with gelatinolytic and keratinolytic activities was observed. This proteolytic activity was fully inhibited by phenylmethylsulphonyl fluoride. These results suggest that the extracellular enzyme belongs to the serine peptidase class. This is the first report of an extracellular serine peptidase produced by C. parapsilosis with keratinolytic activity. The role of this enzyme in yeast-host interactions is discussed.

Human laminin-332 degradation by Candida proteinases

BACKGROUND

Human laminin-332 (Lm-332) degradation by 12 Candida strains and effects of synthetic proteinase inhibitors [Ilomastat (ILM), EDTA, chemically modified tetracycline-3(CMT-3), CMT-308, synthetic peptide CTT-2, and Pefabloc] were studied.

MATERIALS AND METHODS

Laminin-332 was incubated with sonicated cell fractions and 10 times concentrated cell-free fractions of reference and clinical strains of C. albicans, C. dubliniensis, C. guilliermondii, C. glabrata, C. krusei, and C. tropicalis. Proteolysis, pH effects, and inhibitors were analyzed by fluorography and zymography.

RESULTS

Cell fractions of all species except C. guilliermondii and cell-free fractions of C. albicans, and C. dubliniensis showed 20-70 kDa gelatinases at pH 5.0 and 6.0. At pH 7.6, C. glabrata, C. krusei, and C. tropicalis cell fractions and C. tropicalis cell-free fractions showed 55-70 kDa gelatinases. CMT-3, CMT-308, and CTT-2 inhibited Candida gelatinases slightly better than Pefabloc, ILM, and EDTA. No Candida fractions degraded Lm-332 at pH 7.6, but at pH 5.0, 100 kDa bands were generated by cell fractions of C. dubliniensis and C. tropicalis; C. albicans and C. glabrata clinical strains; and C. guilliermondii reference strain. C. krusei reference strain yielded three 100-130 kDa bands. C. albicans, C. dubliniensis, and C. tropicalis reference and clinical strain's cell-free fractions generated 100 kDa band.

CONCLUSIONS

Laminin-332 degradation is pH-dependent and differences exist between studied Candida strains. Lm-332 degradation can exert functional disturbances on basement membrane integrity, possibly aiding Candida cell invasion into tissues. Certain synthetic matrix metalloproteinase inhibitors (CMTs, CTT) can inhibit Candida proteinases and may be therapeutically useful in future.

Biology and pathogenesis of Fonsecaea pedrosoi, the major etiologic agent of chromoblastomycosis

Fonsecaea pedrosoi is the principal etiologic agent of chromoblastomycosis, a fungal disease whose pathogenic events are poorly understood. Treatment of the disease presents poor effectiveness and serious side effects. The disease is epidemiologically important in several regions, which has stimulated studies focused on the biology and pathogenic potential of its major causative agent. In this review, we summarize the current knowledge on the biological aspects of F. pedrosoi, including cell differentiation and pathogenic mechanisms during the interaction of fungi with different hosts' elements.

Multiple gene genealogical analyses suggest divergence and recent clonal dispersal in the opportunistic human pathogen Candida guilliermondii

Candida guilliermondii is a haploid opportunistic pathogen accounting for about 2 % of human blood yeast infections. Recent analyses using multilocus enzyme electrophoresis and karyotyping suggest that strains from human sources traditionally designated C. guilliermondii in fact include at least two species, C. guilliermondii and Candida fermentati. However, the patterns of molecular variation within and between these two species remain largely unknown. In this study, DNA fragments were sequenced from five genes for each of 37 strains collected from Canada, China, the Philippines and Tanzania. The analyses identified significant sequence differences between C. guilliermondii and C. fermentati. The five gene genealogies showed no apparent incongruence, suggesting a predominantly clonal reproductive structure for both species in nature. Indeed, two large clones of C. guilliermondii were identified, with one from Ontario, Canada, and the other from China. Interestingly, the results indicate that strains currently designated C. guilliermondii may contain additional divergent lineages. On the practical side, the results revealed several diagnostic molecular markers that can be used in clinical microbiology laboratories to distinguish C. guilliermondii and C. fermentati. The multiple gene genealogical analyses conducted here revealed significant divergence and clonal dispersal in this important pathogenic yeast complex.

Secretory aspartyl peptidase activity from mycelia of the human fungal pathogen Fonsecaea pedrosoi: effect of HIV aspartyl proteolytic inhibitors

Fonsecaea pedrosoi is the principal causative agent of chromoblastomycosis, which is a chronic, often debilitating, suppurative and granulomatous mycosis. Very little is known about the hydrolytic enzymes produced by this human fungal pathogen. In the present study, we have identified extracellular proteolytic activity from F. pedrosoi mycelial forms when grown in chemically defined conditions. Secretory aspartyl peptidase activity was measured during 15 days of fungal growth in vitro using bovine serum albumin (BSA) as the soluble substrate and extreme acidic pH (2.0). This activity was totally inhibited by pepstatin A, a classic aspartyl peptidase inhibitor. Conversely, metallo (o-phenanthroline), cysteine (E-64) and serine (PMSF) proteolytic inhibitors failed to restrain proteolytic activity. We also evaluated the effect of four distinct HIV aspartyl peptidase inhibitors on the secretory proteolytic activity of F. pedrosoi mycelia. Indinavir, ritonavir and nelfinavir powerfully inhibited extracellular aspartyl proteolytic activity by approximately 97, 96 and 87%, respectively, whereas saquinavir did not significantly interfere with BSA hydrolysis. Mycelial-derived secretory aspartyl peptidase activity cleaved other proteinaceous substrates, including human albumin, fibrinogen, fibronectin, laminin and type I collagen. As previously reported by our group, conidia also produce secretory aspartyl peptidase. In this sense, we investigated the effect of pepstatin A on F. pedrosoi development. Pepstatin A was able to inhibit the growth of conidium and its transformation into mycelium. Taken together, our results suggest a possible participation of aspartyl peptidases in the essential fungal processes, such as growth, differentiation, nutrition and cleavage of relevant host proteinaceous components.

Extracellular Peptidase in the Fungal Pathogen Pseudallescheria boydii

Pseudallescheria boydii is a ubiquitous filamentous fungus capable of causing invasive disease in humans. In the present study, using sodium dodecyl sulfate-polyacrylamide gels containing bovine serum albumin as co-polymerized substrate, we identified a 28-kDa proteolytic activity released to the extracellular environment by mycelia of P. boydii. This peptidase was detected during the growth of P. boydii in Sabouraud-dextrose medium for 13 days and reached its maximal production on day 7. The 28-kDa peptidase was active in acidic pH (5.5) and had its activity completely blocked by 1,10-phenanthroline, a potent zinc-metallopeptidase inhibitor. Two other metallopeptidase inhibitors, EDTA and EGTA, were also tested and no alterations were observed in the activity of the 28-kDa extracellular peptidase. Likewise, E-64 (a cysteine peptidase inhibitor), phenylmethylsulphonyl fluoride (a serine peptidase inhibitor), and pepstatin A (an aspartyl peptidase inhibitor) did not significantly alter the enzymatic behavior. Collectively, we described for the first time the expression of an extracellular metallopeptidase in the human opportunistic fungal pathogen P. boydii.

Pseudallescheria boydii releases metallopeptidases capable of cleaving several proteinaceous compounds

Pseudallescheria boydii is an opportunistic filamentous fungus that causes serious infections in humans. Virulence attributes expressed by P. boydii are unknown. Conversely, peptidases are incriminated as virulence factors in several pathogenic fungi. Here we investigated the extracellular peptidase profile in P. boydii. After growth on Sabouraud for 7 days, mycelia of P. boydii were incubated for 20 h in PBS-glucose. The cell-free PBS-glucose supernatant was submitted to SDS-PAGE and 12 secretory polypeptides were observed. Two of these polypeptides (28 and 35 kD) presented proteolytic activity when BSA was used as a copolymerized substrate. The extracellular peptidases were most active in acidic pH (5.5) and fully inhibited by 1,10-phenanthroline, a zinc-metallopeptidase inhibitor. Other metallo-, cysteine, serine and aspartic proteolytic inhibitors did not significantly alter these activities. To confirm that these enzymes belong to the metallo-type peptidases, the apoenzymes were obtained by dialysis against chelating agents, and supplementation with different cations, especially Cu(2+) and Zn(2+), restored their activities. Except for gelatin, both metallopeptidases hydrolyzed various co-polymerized substrates, including human serum albumin, casein, hemoglobin and IgG. Additionally, the metallopeptidases were able to cleave different soluble proteinaceous substrates such as extracellular matrix components and sialylated proteins. All these hydrolyses were inhibited by 1,10-phenanthroline. Interestingly, Scedosporium apiospermum (the anamorph of P. boydii) produced a distinct extracellular peptidase profile. Collectively, our results demonstrated for the first time the expression of acidic extracellular metallopeptidases in P. boydii capable of degrading several proteinaceous compounds that could help the fungus to escape from natural human barriers and defenses.