Surface Glycans of Candida albicans and Other Pathogenic Fungi: Physiological Roles, Clinical Uses, and Experimental Challenges

SUMMARY Although fungi have always been with us as commensals and pathogens, fungal infections have been increasing in frequency over the past few decades. There is a growing body of literature describing the involvement of carbohydrate groups in various aspects of fungal disease. Carbohydrates comprising the cell wall or capsule, or as a component of glycoproteins, are the fungal cell surface entities most likely to be exposed to the surrounding environment. Thus, the fungus-host interaction is likely to involve carbohydrates before DNA, RNA, or even protein. The interaction between fungal and host cells is also complex, and early studies using whole cells or crude cell fractions often produced seemingly conflicting results. What was needed, and what has been developing, is the ability to identify specific glycan structures and determine how they interact with immune system components. Carbohydrate analysis is complicated by the complexity of glycan structures and by the challenges of separating and detecting carbohydrates experimentally. Advances in carbohydrate chemistry have enabled us to move from the foundation of composition analysis to more rapid characterization of specific structures. This, in turn, will lead to a greater understanding of how fungi coexist with their hosts as commensals or exist in conflict as pathogens.

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Targeting adhesion in fungal pathogen Candida albicans

Future Medicinal Chemistry ◽

10.4155/fmc-2020-0052 ◽

2020 ◽

Author(s):

Harlei Martin ◽

Kevin Kavanagh ◽

Trinidad Velasco-Torrijos

Keyword(s):

Candida Albicans ◽

Fungal Infections ◽

Initial Step ◽

Infection Process ◽

Host Cells ◽

Fungal Cell ◽

Receptor Interactions ◽

Genes Encoding ◽

Invasive Infections ◽

Wall Components

Fungal infections with increasing resistance to conventional therapies are a growing concern. Candida albicans is a major opportunistic yeast responsible for mucosal and invasive infections. Targeting the initial step of the infection process (i.e., C. albicans adhesion to the host cell) is a promising strategy. A wide variety of molecules can interfere with adhesion processes via an assortment of mechanisms. Herein, we focus on how small molecules disrupt biosynthesis of fungal cell wall components and membrane structure, prevent the localization of GPI-anchor proteins, inhibit production of enzymes involved in adhesion, downregulate genes encoding adhesins and competitively inhibit receptor interactions. As a result, adhesion of C. albicans to host cells is reduced, paving the way to new classes of antifungal agents.

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Characteristics of Extracellular Vesicles Released by the Pathogenic Yeast-Like Fungi Candida glabrata, Candida parapsilosis and Candida tropicalis

Cells ◽

10.3390/cells9071722 ◽

2020 ◽

Vol 9 (7) ◽

pp. 1722 ◽

Cited By ~ 4

Author(s):

Justyna Karkowska-Kuleta ◽

Kamila Kulig ◽

Elzbieta Karnas ◽

Ewa Zuba-Surma ◽

Olga Woznicka ◽

...

Keyword(s):

Extracellular Vesicles ◽

Phosphoglycerate Kinase ◽

Host Cells ◽

Opportunistic Pathogens ◽

Candida Spp ◽

Fungal Cell ◽

Pathogenic Yeast ◽

Cytoplasmic Proteins ◽

Candidal Species

Candida spp. yeast-like fungi are opportunistic pathogens in humans and have been recently found to release extracellular vesicles (EVs) that are involved in many vital biological processes in fungal cells. These include communication between microorganisms and host–pathogen interactions during infection. The production of EVs and their content have been significantly characterized in the most common candidal species Candida albicans, including the identification of numerous virulence factors and cytoplasmic proteins in the EV cargo. We have here conducted the isolation and proteomic characterization of EVs produced by the clinically important non-albicans Candida species C. glabrata, C. tropicalis and C. parapsilosis. With the use of ultracentrifugation of the cell-free culture supernatant, the candidal EVs were collected and found to be a heterogeneous population of particles for each species with sizes ranging from 60–280 nm. The proteinaceous contents of these vesicles were analyzed using LC-MS/MS, with particular attention paid to surface-expressed proteins that would come into immediate and direct contact with host cells. We thereby identified 42 extracellular and surface-connected proteins from C. glabrata, 33 from C. parapsilosis, and 34 from C. tropicalis, including membrane-associated transporters, glycoproteins and enzymes involved in the organization of the fungal cell wall, as well as several cytoplasmic proteins, including alcohol dehydrogenase, enolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and pyruvate kinase, for which the vesicular transport is a possible mechanism underlying their non-classical secretion.

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Identification of a New Class of Antifungals Targeting the Synthesis of Fungal Sphingolipids

mBio ◽

10.1128/mbio.00647-15 ◽

2015 ◽

Vol 6 (3) ◽

Cited By ~ 64

Author(s):

Visesato Mor ◽

Antonella Rella ◽

Amir M. Farnoud ◽

Ashutosh Singh ◽

Mansa Munshi ◽

...

Keyword(s):

Cell Cycle Progression ◽

Fungal Infections ◽

Pathogenic Fungi ◽

Antifungal Drugs ◽

Sequencing Analysis ◽

Fungal Cell ◽

New Class ◽

Narrow Spectrum

ABSTRACT Recent estimates suggest that >300 million people are afflicted by serious fungal infections worldwide. Current antifungal drugs are static and toxic and/or have a narrow spectrum of activity. Thus, there is an urgent need for the development of new antifungal drugs. The fungal sphingolipid glucosylceramide (GlcCer) is critical in promoting virulence of a variety of human-pathogenic fungi. In this study, we screened a synthetic drug library for compounds that target the synthesis of fungal, but not mammalian, GlcCer and found two compounds [N′-(3-bromo-4-hydroxybenzylidene)-2-methylbenzohydrazide (BHBM) and its derivative, 3-bromo-N′-(3-bromo-4-hydroxybenzylidene) benzohydrazide (D0)] that were highly effective in vitro and in vivo against several pathogenic fungi. BHBM and D0 were well tolerated in animals and are highly synergistic or additive to current antifungals. BHBM and D0 significantly affected fungal cell morphology and resulted in the accumulation of intracellular vesicles. Deep-sequencing analysis of drug-resistant mutants revealed that four protein products, encoded by genes APL5, COS111, MKK1, and STE2, which are involved in vesicular transport and cell cycle progression, are targeted by BHBM. IMPORTANCE Fungal infections are a significant cause of morbidity and mortality worldwide. Current antifungal drugs suffer from various drawbacks, including toxicity, drug resistance, and narrow spectrum of activity. In this study, we have demonstrated that pharmaceutical inhibition of fungal glucosylceramide presents a new opportunity to treat cryptococcosis and various other fungal infections. In addition to being effective against pathogenic fungi, the compounds discovered in this study were well tolerated by animals and additive to current antifungals. These findings suggest that these drugs might pave the way for the development of a new class of antifungals.

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Hitting the Caspofungin Salvage Pathway of Human-Pathogenic Fungi with the Novel Lasso Peptide Humidimycin (MDN-0010)

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00683-15 ◽

2015 ◽

Vol 59 (9) ◽

pp. 5145-5153 ◽

Cited By ~ 23

Author(s):

Vito Valiante ◽

Maria Cândida Monteiro ◽

Jesús Martín ◽

Robert Altwasser ◽

Noureddine El Aouad ◽

...

Keyword(s):

Fungal Infections ◽

Pathogenic Fungi ◽

Major Effect ◽

Strong Increase ◽

The Novel ◽

Salvage Pathway ◽

Fungal Cell ◽

Content Type ◽

High Osmolarity Glycerol ◽

Microbial Extracts

ABSTRACTFungal infections have increased dramatically in the last 2 decades, and fighting infectious diseases requires innovative approaches such as the combination of two drugs acting on different targets or even targeting a salvage pathway of one of the drugs. The fungal cell wall biosynthesis is inhibited by the clinically used antifungal drug caspofungin. This antifungal activity has been found to be potentiated by humidimycin, a new natural product identified from the screening of a collection of 20,000 microbial extracts, which has no major effect when used alone. An analysis of transcriptomes and selectedAspergillus fumigatusmutants indicated that humidimycin affects the high osmolarity glycerol response pathway. By combining humidimycin and caspofungin, a strong increase in caspofungin efficacy was achieved, demonstrating that targeting different signaling pathways provides an excellent basis to develop novel anti-infective strategies.

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Overview of the Interplay Between Cell Wall Integrity Signaling Pathways and Membrane Lipid Biosynthesis in Fungi: Perspectives forAspergillus fumigatus

Current Protein and Peptide Science ◽

10.2174/1389203720666190705164203 ◽

2020 ◽

Vol 21 (3) ◽

pp. 265-283 ◽

Cited By ~ 1

Author(s):

João Henrique T.M. Fabri ◽

Marina C. Rocha ◽

Iran Malavazi

Keyword(s):

Cell Wall ◽

Plasma Membrane ◽

Signaling Pathways ◽

Fungal Infections ◽

Invasive Pulmonary Aspergillosis ◽

Pathogenic Fungi ◽

Cell Wall Integrity ◽

Immune Recognition ◽

Fungal Cell ◽

Low Efficiency

:The cell wall (CW) and plasma membrane are fundamental structures that define cell shape and support different cellular functions. In pathogenic fungi, such as Aspegillus fumigatus, they not only play structural roles but are also important for virulence and immune recognition. Both the CW and the plasma membrane remain as attractive drug targets to treat fungal infections, such as the Invasive Pulmonary Aspergillosis (IPA), a disease associated with high morbimortality in immunocompromised individuals. The low efficiency of echinocandins that target the fungal CW biosynthesis, the occurrence of environmental isolates resistant to azoles such as voriconazole and the known drawbacks associated with amphotericin toxicity foster the urgent need for fungal-specific drugable targets and/or more efficient combinatorial therapeutic strategies. Reverse genetic approaches in fungi unveil that perturbations of the CW also render cells with increased susceptibility to membrane disrupting agents and vice-versa. However, how the fungal cells simultaneously cope with perturbation in CW polysaccharides and cell membrane proteins to allow morphogenesis is scarcely known. Here, we focus on current information on how the main signaling pathways that maintain fungal cell wall integrity, such as the Cell Wall Integrity and the High Osmolarity Glycerol pathways, in different species often cross-talk to regulate the synthesis of molecules that comprise the plasma membrane, especially sphingolipids, ergosterol and phospholipids to promote functioning of both structures concomitantly and thus, cell viability. We propose that the conclusions drawn from other organisms are the foundations to point out experimental lines that can be endeavored in A. fumigatus.

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Steroid-Functionalized Imidazolium Salts with an Extended Spectrum of Antifungal and Antibacterial Activity

International Journal of Molecular Sciences ◽

10.3390/ijms222212180 ◽

2021 ◽

Vol 22 (22) ◽

pp. 12180

Author(s):

Marta Malinowska ◽

Diana Sawicka ◽

Katarzyna Niemirowicz-Laskowska ◽

Przemysław Wielgat ◽

Halina Car ◽

...

Keyword(s):

High Resolution Mass Spectrometry ◽

Fungal Infections ◽

Lithocholic Acid ◽

Pathogenic Fungi ◽

Antifungal Drugs ◽

Host Cells ◽

Microsporum Canis ◽

Human Pathogens ◽

Imidazolium Salts ◽

13C Nuclear Magnetic Resonance

It is established that high rates of morbidity and mortality caused by fungal infections are related to the current limited number of antifungal drugs and the toxicity of these agents. Imidazolium salts as azole derivatives can be successfully used in the treatment of fungal infections in humans. Steroid-functionalized imidazolium salts were synthesized using a new, more efficient method. As a result, 20 salts were obtained with high yields, 12 of which were synthesized and characterized for the first time. They were derivatives of lithocholic acid and 3-oxo-23,24-dinorchol-4-ene-22-al and were fully characterized by 1H and 13C nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and high resolution mass spectrometry (HRMS). Due to the excellent activity against bacteria and Candida albicans, new research was extended to include tests on five species of pathogenic fungi and molds: Aspergillus niger ATCC 16888, Aspergillus fumigatus ATCC 204305, Trichophyton mentagrophytes ATCC 9533, Cryptococcus neoformans ATCC 14116, and Microsporum canis ATCC 11621. The results showed that the new salts are almost universal antifungal agents and have a broad spectrum of activity against other human pathogens. To initially assess the safety of the synthesized salts, hemocompatibility with host cells and cytotoxicity were also examined. No toxicity was observed at the concentration at which the compounds were active against pathogens.

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Reovirus Cell Entry Requires Functional Microtubules

mBio ◽

10.1128/mbio.00405-13 ◽

2013 ◽

Vol 4 (4) ◽

Cited By ~ 40

Author(s):

Bernardo A. Mainou ◽

Paula F. Zamora ◽

Alison W. Ashbrook ◽

Daniel C. Dorset ◽

Kwang S. Kim ◽

...

Keyword(s):

Cell Attachment ◽

Endocytic Pathway ◽

Cell Entry ◽

Host Cells ◽

Microtubule Inhibitors ◽

Viral Particles ◽

Microtubule Motor ◽

Cellular Mediators ◽

Rapid Characterization

ABSTRACTMammalian reovirus binds to cell-surface glycans and junctional adhesion molecule A and enters cells by receptor-mediated endocytosis in a process dependent on β1 integrin. Within the endocytic compartment, reovirus undergoes stepwise disassembly, allowing release of the transcriptionally active viral core into the cytoplasm. To identify cellular mediators of reovirus infectivity, we screened a library of small-molecule inhibitors for the capacity to block virus-induced cytotoxicity. In this screen, reovirus-induced cell killing was dampened by several compounds known to impair microtubule dynamics. Microtubule inhibitors were assessed for blockade of various stages of the reovirus life cycle. While these drugs did not alter reovirus cell attachment or internalization, microtubule inhibitors diminished viral disassembly kinetics with a concomitant decrease in infectivity. Reovirus virions colocalize with microtubules and microtubule motor dynein 1 during cell entry, and depolymerization of microtubules results in intracellular aggregation of viral particles. These data indicate that functional microtubules are required for proper sorting of reovirus virions following internalization and point to a new drug target for pathogens that use the endocytic pathway to invade host cells.IMPORTANCEScreening libraries of well-characterized drugs for antiviral activity enables the rapid characterization of host processes required for viral infectivity and provides new therapeutic applications for established pharmaceuticals. Our finding that microtubule-inhibiting drugs impair reovirus infection identifies a new cell-based antiviral target.

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Plant Antifungal Lectins: Mechanism of Action and Targets on Human Pathogenic Fungi

Current Protein and Peptide Science ◽

10.2174/1389203720666190906164448 ◽

2020 ◽

Vol 21 (3) ◽

pp. 284-294 ◽

Cited By ~ 1

Author(s):

Marianela Del Rio ◽

Laura de la Canal ◽

Mariana Regente

Keyword(s):

Biological Function ◽

Fungal Infections ◽

Current Knowledge ◽

Pathogenic Fungi ◽

Action Mechanism ◽

Fungal Cell ◽

Natural Sources ◽

Improve Treatment ◽

Antifungal Action ◽

Reduced Group

Lectins are proteins characterized by their ability to specifically bind different carbohydrate motifs. This feature is associated with their endogenous biological function as well as with multiple applications. Plants are important natural sources of these proteins; however, only a reduced group was shown to display antifungal activity. Although it is hypothesized that the target of lectins is the fungal cell wall, the mechanism through which they exert the antifungal action is poorly understood. This topic is relevant to improve treatment against pathogens of importance for human health. In this context, mechanisms pointing to essential attributes for virulence instead of the viability of the pathogen emerge as a promising approach. This review provides the current knowledge on the action mechanism of plant antifungal lectins and their putative use for the development of novel active principles against fungal infections.

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Structural and Bioactivity Characterization of Filipin Derivatives from Engineered Streptomyces filipinensis Strains Reveals Clues for Reduced Haemolytic Action

Antibiotics ◽

10.3390/antibiotics9070413 ◽

2020 ◽

Vol 9 (7) ◽

pp. 413

Author(s):

Eva G. Barreales ◽

Ángel Rumbero ◽

Tamara D. Payero ◽

Antonio de Pedro ◽

Ester Jambrina ◽

...

Keyword(s):

Antifungal Activity ◽

Fungal Infections ◽

Pathogenic Fungi ◽

New Drugs ◽

Metabolic Intermediates ◽

Microdilution Method ◽

Broth Microdilution Method ◽

Opportunistic Pathogenic

The rise in the number of immunocompromised patients has led to an increased incidence of fungal infections, with high rates of morbidity and mortality. Furthermore, misuse of antifungals has boosted the number of resistant strains to these agents; thus, there is urgent need for new drugs against these infections. Here, the in vitro antifungal activity of filipin III metabolic intermediates has been characterized against a battery of opportunistic pathogenic fungi—Candida albicans, Candida glabrata, Candida krusei, Cryptococcus neoformans, Trichosporon cutaneum, Trichosporon asahii, Aspergillus nidulans, Aspergillus niger, and Aspergillus fumigatus—using the Clinical and Laboratory Standards Institute broth microdilution method. Structural characterization of these compounds was undertaken by mass spectrometry (MS) and nuclear magnetic resonance (NMR) following HPLC purification. Complete NMR assignments were obtained for the first time for filipins I and II. In vitro haemolytic assays revealed that the haemolytic action of these compounds relies largely on the presence of a hydroxyl function at C26, since derivatives lacking such moiety show remarkably reduced activity. Two of these derivatives, 1′-hydroxyfilipin I and filipin I, show decreased toxicity towards cholesterol-containing membranes while retaining potent antifungal activity, and could constitute excellent leads for the development of efficient pharmaceuticals, particularly against Cryptococcosis.

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Preliminary Characterisation of NP339, a Novel Polyarginine Peptide with Broad Antifungal Activity

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02345-20 ◽

2021 ◽

Author(s):

Vanessa Duncan ◽

Daniel Smith ◽

Laura Simpson ◽

Emma Lovie ◽

Laura Katvars ◽

...

Keyword(s):

Antifungal Agents ◽

Fungal Infections ◽

Pathogenic Fungi ◽

Drug Resistant ◽

Murine Models ◽

Therapeutic Application ◽

Fungal Cell ◽

Pathogenic Microbes ◽

A Charge

Fungi cause disease in nearly one billion individuals worldwide. Only three classes of antifungal agents are currently available in mainstream clinical use. Emerging and drug resistant fungi, toxicity, and drug–drug interactions compromise their efficacy and applicability. Consequently, new and improved antifungal therapies are urgently needed. In response to that need, we have developed NP339, a 2-kDa polyarginine peptide that is active against pathogenic fungi from the genera Candida, Aspergillus, Cryptococcus, and others. NP339 was designed based on endogenous cationic human defence peptides, which are constituents of the cornerstone of immune defence against pathogenic microbes. NP339 specifically targets the fungal cell membrane through a charge-charge initiated, membrane interaction and therefore possesses a differentiated safety and toxicity profile to existing antifungal classes. NP339 is rapidly fungicidal and does not elicit resistance in target fungi upon extensive passaging in vitro. Preliminary analyses in murine models indicate scope for therapeutic application of NP339 against a range of systemic and mucocutaneous fungal infections. Collectively, these data indicate that NP339 can be developed into a highly differentiated, first-in-class antifungal candidate for poorly served invasive and other serious fungal diseases.

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