Lipid-Binding Aegerolysin from Biocontrol Fungus Beauveria bassiana

Fungi are the most common pathogens of insects and thus important regulators of their populations. Lipid-binding aegerolysin proteins, which are commonly found in the fungal kingdom, may be involved in several biologically relevant processes including attack and defense against other organisms. Aegerolysins act alone or together with membrane-attack-complex/perforin (MACPF)-like proteins to form transmembrane pores that lead to cell lysis. We performed an in-depth bioinformatics analysis of aegerolysins in entomopathogenic fungi and selected a candidate aegerolysin, beauveriolysin A (BlyA) from Beauveria bassiana. BlyA was expressed as a recombinant protein in Escherichia coli, and purified to further determine its functional and structural properties, including lipid-binding ability. Aegerolysins were found to be encoded in genomes of entomopathogenic fungi, such as Beauveria, Cordyceps, Metarhizium and Ophiocordyceps. Detailed bioinformatics analysis revealed that they are linked to MACPF-like genes in most genomes. We also show that BlyA interacts with an insect-specific membrane lipid. These results were placed in the context of other fungal and bacterial aegerolysins and their partner proteins. We believe that aegerolysins play a role in promoting the entomopathogenic and antagonistic activity of B. bassiana, which is an active ingredient of bioinsecticides.

Unconventional Secretion of Nigerolysins A from Aspergillus Species

Aegerolysins are small lipid-binding proteins particularly abundant in fungi. Aegerolysins from oyster mushrooms interact with an insect-specific membrane lipid and, together with MACPF proteins produced by the same organism, form pesticidal pore-forming complexes. The specific interaction with the same membrane lipid was recently demonstrated for nigerolysin A2 (NigA2), an aegerolysin from Aspergillus niger. In Aspergillus species, the aegerolysins were frequently found as secreted proteins, indicating their function in fungal defense. Using immunocytochemistry and live-cell imaging we investigated the subcellular localization of the nigerolysins A in A. niger, while their secretion was addressed by secretion prediction and Western blotting. We show that both nigerolysins A are leaderless proteins that reach the cell exterior by an unconventional protein secretion. NigA proteins are evenly distributed in the cytoplasm of fungal hyphae. A detailed bioinformatics analysis of Aspergillus aegerolysins suggests that the same function occurs only in a limited number of aegerolysins. From alignment, analysis of chromosomal loci, orthology, synteny, and phylogeny it follows that the same or a similar function described for pairs of pesticidal proteins of Pleurotus sp. can be expected in species of the subgenus Circumdati, section Nigri, series Nigri, and some other species with adjacent pairs of putative pesticidal proteins.

Growing a circular economy with fungal biotechnology: a white paper

Fungi have the ability to transform organic materials into a rich and diverse set of useful products and provide distinct opportunities for tackling the urgent challenges before all humans. Fungal biotechnology can advance the transition from our petroleum-based economy into a bio-based circular economy and has the ability to sustainably produce resilient sources of food, feed, chemicals, fuels, textiles, and materials for construction, automotive and transportation industries, for furniture and beyond. Fungal biotechnology offers solutions for securing, stabilizing and enhancing the food supply for a growing human population, while simultaneously lowering greenhouse gas emissions. Fungal biotechnology has, thus, the potential to make a significant contribution to climate change mitigation and meeting the United Nation’s sustainable development goals through the rational improvement of new and established fungal cell factories. The White Paper presented here is the result of the 2nd Think Tank meeting held by the EUROFUNG consortium in Berlin in October 2019. This paper highlights discussions on current opportunities and research challenges in fungal biotechnology and aims to inform scientists, educators, the general public, industrial stakeholders and policymakers about the current fungal biotech revolution.

Functional studies of aegerolysin and MACPF-like proteins in Aspergillus niger

Proteins of the aegerolysin family have a high abundance in Fungi. Due to their specific binding to membrane lipids, and their membrane-permeabilization potential in concert with protein partner(s) belonging to a membrane-attack-complex/perforin (MACPF) superfamily, they were proposed as useful tools in different biotechnological and biomedical applications. In this work, we performed functional studies on expression of the genes encoding aegerolysin and MACPF-like proteins in Aspergillus niger. Our results suggest the sporulation process being crucial for strong induction of the expression of all these genes. However, deletion of either of the aegerolysin genes did not influence the growth, development, sporulation efficiency and phenotype of the mutants, indicating that aegerolysins are not key factors in the sporulation process. In all our expression studies we noticed a strong correlation in the expression of one aegerolysin and MACPF-like gene. Aegerolysins were confirmed to be secreted from the fungus. We also showed the specific interaction of a recombinant A. niger aegerolysin with an invertebrate-specific membrane sphingolipid. Moreover, using this protein labelled with mCherry we successfully stained insect cells membranes containing this particular sphingolipid. Our combined results suggest, that aegerolysins in this species, and probably also in other aspergilli, could be involved in defence against predators.

Aegerolysins: Lipid-binding proteins with versatile functions

Proteins of the aegerolysin family span many kingdoms of life. They are relatively widely distributed in bacteria and fungi, but also appear in plants, protozoa and insects. Despite being produced in abundance in cells at specific developmental stages and present in secretomes, only a few aegerolysins have been studied in detail. In particular, their organism-specific physiological roles are intriguing. Here, we review published findings to date on the distribution, molecular interactions and biological activities of this family of structurally and functionally versatile proteins, the aegerolysins.

Comparative genomics reveals high biological diversity and specific adaptations in the industrially and medically important fungal genus Aspergillus

BACKGROUND

The fungal genus Aspergillus is of critical importance to humankind. Species include those with industrial applications, important pathogens of humans, animals and crops, a source of potent carcinogenic contaminants of food, and an important genetic model. The genome sequences of eight aspergilli have already been explored to investigate aspects of fungal biology, raising questions about evolution and specialization within this genus.

RESULTS

We have generated genome sequences for ten novel, highly diverse Aspergillus species and compared these in detail to sister and more distant genera. Comparative studies of key aspects of fungal biology, including primary and secondary metabolism, stress response, biomass degradation, and signal transduction, revealed both conservation and diversity among the species. Observed genomic differences were validated with experimental studies. This revealed several highlights, such as the potential for sex in asexual species, organic acid production genes being a key feature of black aspergilli, alternative approaches for degrading plant biomass, and indications for the genetic basis of stress response. A genome-wide phylogenetic analysis demonstrated in detail the relationship of the newly genome sequenced species with other aspergilli.

CONCLUSIONS

Many aspects of biological differences between fungal species cannot be explained by current knowledge obtained from genome sequences. The comparative genomics and experimental study, presented here, allows for the first time a genus-wide view of the biological diversity of the aspergilli and in many, but not all, cases linked genome differences to phenotype. Insights gained could be exploited for biotechnological and medical applications of fungi.

How to Study Protein-protein Interactions

Physical and functional interactions between molecules in living systems are central to all biological processes. Identification of protein complexes therefore is becoming increasingly important to gain a molecular understanding of cells and organisms. Several powerful methodologies and techniques have been developed to study molecular interactions and thus help elucidate their nature and role in biology as well as potential ways how to interfere with them. All different techniques used in these studies have their strengths and weaknesses and since they are mostly employed in in vitro conditions, a single approach can hardly accurately reproduce interactions that happen under physiological conditions. However, complementary usage of as many as possible available techniques can lead to relatively realistic picture of the biological process. Here we describe several proteomic, biophysical and structural tools that help us understand the nature and mechanism of these interactions.

Fungal aegerolysin-like proteins: distribution, activities, and applications

The aegerolysin protein family (from aegerolysin of the mushroom Agrocybe aegerita) comprises proteins of ∼15-20 kDa from various eukaryotic and bacterial taxa. Aegerolysins are inconsistently distributed among fungal species, and variable numbers of homologs have been reported for species within the same genus. As such noncore proteins, without a member of a protein family in each of the sequenced fungi, they can give insight into different species-specific processes. Some aegerolysins have been reported to be hemolytically active against mammalian erythrocytes. However, some function as bi-component proteins that have membrane activity in concert with another protein that contains a membrane attack complex/perforin domain. The function of most of aegerolysins is unknown, although some have been suggested to have a role in development of the organism. Potential biotechnological applications of aegerolysins are already evident, despite the limited scientific knowledge available at present. Some mushroom aegerolysins, for example, can be used as markers to detect and label specific membrane lipids. Others can be used as biomarkers of fungal exposure, where their genes can serve as targets for detection of fungi and their progression during infectious diseases. Antibodies against aegerolysins can also be raised as immuno-diagnostic tools. Aegerolysins have been shown to serve as a species determination tool for fungal phytopathogen isolates in terms of some closely related species, where commonly used internal transcribed spacer barcoding has failed. Moreover, strong promoters that regulate aegerolysin genes can promote secretion of heterologous proteins from fungi and have been successfully applied in simultaneous multi-gene expression techniques.

Cytochrome P450 monooxygenase CYP53 family in fungi: comparative structural and evolutionary analysis and its role as a common alternative anti-fungal drug target

Cytochrome P450 monooxygenases (CYPs/P450s) are heme-thiolate proteins whose role as a drug target against pathogenic microbes has been explored because of their stereo- and regio-specific oxidation activity. We aimed to assess the CYP53 family's role as a common alternative drug target against animal (including human) and plant pathogenic fungi and its role in fungal-mediated wood degradation. Genome-wide analysis of fungal species revealed the presence of CYP53 members in ascomycetes and basidiomycetes. Basidiomycetes had a higher number of CYP53 members in their genomes than ascomycetes. Only two CYP53 subfamilies were found in ascomycetes and six subfamilies in basidiomycetes, suggesting that during the divergence of phyla ascomycetes lost CYP53 P450s. According to phylogenetic and gene-structure analysis, enrichment of CYP53 P450s in basidiomycetes occurred due to the extensive duplication of CYP53 P450s in their genomes. Numerous amino acids (103) were found to be conserved in the ascomycetes CYP53 P450s, against only seven in basidiomycetes CYP53 P450s. 3D-modelling and active-site cavity mapping data revealed that the ascomycetes CYP53 P450s have a highly conserved protein structure whereby 78% amino acids in the active-site cavity were found to be conserved. Because of this rigid nature of ascomycetes CYP53 P450s' active site cavity, any inhibitor directed against this P450 family can serve as a common anti-fungal drug target, particularly toward pathogenic ascomycetes. The dynamic nature of basidiomycetes CYP53 P450s at a gene and protein level indicates that these P450s are destined to acquire novel functions. Functional analysis of CYP53 P450s strongly supported our hypothesis that the ascomycetes CYP53 P450s ability is limited for detoxification of toxic molecules, whereas basidiomycetes CYP53 P450s play an additional role, i.e. involvement in degradation of wood and its derived components. This study is the first report on genome-wide comparative structural (gene and protein structure-level) and evolutionary analysis of a fungal P450 family.

Targeted lipid analysis of haemolytic mycelial extracts of Aspergillus niger

Ethanolic extracts of mycelia from Aspergillus niger (strain N402) grown in liquid media were observed to have haemolytic activity on bovine erythrocytes. This haemolytic activity decreased significantly during the time of growth (1-3 days). Moreover, when A. niger was grown on carbon-deprived medium, the efficiency of this haemolytic activity in the ethanolic extracts was much lower than when grown in carbon-enriched medium, and became almost undetectable after 3 days of growth in carbon-deprived medium. The lipid composition of these ethanolic extracts was analysed by liquid chromatography-electrospray ionisation tandem mass spectrometry. This haemolytic activity can be mainly linked to the relative levels of the molar ratios of the unsaturated fatty acids and lysophosphatidylcholines.

Antifungal activity of cinnamic acid derivatives involves inhibition of benzoate 4-hydroxylase (CYP53)

AIMS

CYP53A15, from the sorghum pathogen Cochliobolus lunatus, is involved in detoxification of benzoate, a key intermediate in aromatic compound metabolism in fungi. Because this enzyme is unique to fungi, it is a promising drug target in fungal pathogens of other eukaryotes.

METHODS AND RESULTS

In our work, we showed high antifungal activity of seven cinnamic acid derivatives against C. lunatus and two other fungi, Aspergillus niger and Pleurotus ostreatus. To elucidate the mechanism of action of cinnamic acid derivatives with the most potent antifungal properties, we studied the interactions between these compounds and the active site of C. lunatus cytochrome P450, CYP53A15.

CONCLUSION

We demonstrated that cinnamic acid and at least four of the 42 tested derivatives inhibit CYP53A15 enzymatic activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

By identifying selected derivatives of cinnamic acid as possible antifungal drugs, and CYP53 family enzymes as their targets, we revealed a potential inhibitor-target system for antifungal drug development.

Human granulocyte colony stimulating factor (G-CSF) produced in the filamentous fungus Aspergillus niger

For the first time, a fungal production system is described for expression and secretion of the medically important human protein G-CSF, in Aspergillus niger. A reliable strategy was chosen with in-frame fusion of G-CSF behind a KEX2 cleavage site downstream of the coding region of the highly secreted homologous glucoamylase. This provided secretion levels of 5-10 mg/l culture medium of correctly processed G-CSF, although the majority of the protein (>90%) was biologically inactive. Following denaturation/ concentration and chromatographic separation/ renaturation, the G-CSF proliferation activity increased considerably, and analytical immobilised metal affinity chromatography confirmed the monomeric and correctly folded protein. These data suggest that this human secretory protein secreted into the medium of A. niger was not correctly folded, and that it escaped the endoplasmic reticulum folding control systems. This is compared to the folding of G-CSF produced in bacteria and yeast.

Distribution of MACPF/CDC proteins

Membrane Attack Complex/Perforin (MACPF) and Cholesterol-Dependent Cytolysins (CDC) form the MACPF/CDC superfamily of important effector proteins widespread in nature. MACPFs and CDCs were discovered separately with no sequence similarity at that stage being apparent between the two protein families such that they were not, until recently, considered evolutionary related. The breakthrough showing they are came with recent structural work that also shed light on the molecular mechanism of action of various MACPF proteins. Similarity in structural properties and conserved functional features indicate that both protein families have the same evolutionary origin. We will describe the distribution of MACPF/CDC proteins in nature and discuss briefly their similarity and functional role in different biological processes.

The versatility of the fungal cytochrome P450 monooxygenase system is instrumental in xenobiotic detoxification

Cytochromes P450 (CYPs) catalyse diverse reactions and are key enzymes in fungal primary and secondary metabolism, and xenobiotic detoxification. CYP enzymatic properties and substrate specificity determine the reaction outcome. However, CYP-mediated reactions may also be influenced by their redox partners. Filamentous fungi with numerous CYPs often possess multiple microsomal redox partners, cytochrome P450 reductases (CPRs). In the plant pathogenic ascomycete Cochliobolus lunatus we recently identified two CPR paralogues, CPR1 and CPR2. Our objective was to functionally characterize two endogenous fungal cytochrome P450 systems and elucidate the putative physiological roles of CPR1 and CPR2. We reconstituted both CPRs with CYP53A15, or benzoate 4-hydroxylase from C. lunatus, which is crucial in the detoxification of phenolic plant defence compounds. Biochemical characterization using RP-HPLC shows that both redox partners support CYP activity, but with different product specificities. When reconstituted with CPR1, CYP53A15 converts benzoic acid to 4-hydroxybenzoic acid, and 3-methoxybenzoic acid to 3-hydroxybenzoic acid. However, when the redox partner is CPR2, both substrates are converted to 3,4-dihydroxybenzoic acid. Deletion mutants and gene expression in mycelia grown on media with inhibitors indicate that CPR1 is important in primary metabolism, whereas CPR2 plays a role in xenobiotic detoxification.