Glycosyl phosphatidylinositol-dependent cross-linking of alpha-agglutinin and beta 1,6-glucan in the Saccharomyces cerevisiae cell wall

Yeast surface display technology: Mechanisms, applications, and perspectives

Microbial cell surface display technology, which relies on genetically fusing heterologous target proteins to the cell wall through fusion with cell wall anchor proteins, has emerged as a promising and powerful method with diverse applications in biotechnology and biomedicine. Compared to classical intracellular or extracellular expression (secretion) systems, the cell surface display strategy stands out by eliminating the necessity for enzyme purification, overcoming substrate transport limitations, and demonstrating enhanced activity, stability, and selectivity. Unlike phage or bacterial surface display, the yeast surface display (YSD) system offers distinct advantages, including its large cell size, ease of culture and genetic manipulation, the use of generally regarded as safe (GRAS) host cell, the ability to ensure correct folding of complex eukaryotic proteins, and the potential for post-translational modifications. To date, YSD systems have found widespread applications in protein engineering, waste biorefineries, bioremediation, and the production of biocatalysts and biosensors. This review focuses on detailing various strategies and mechanisms for constructing YSD systems, providing a comprehensive overview of both fundamental principles and practical applications. Finally, the review outlines future perspectives for developing novel forms of YSD systems and explores potential applications in diverse fields.

Utilization of Macroalgae for the Production of Bioactive Compounds and Bioprocesses Using Microbial Biotechnology

To achieve sustainable development, alternative resources should replace conventional resources such as fossil fuels. In marine ecosystems, many macroalgae grow faster than terrestrial plants. Macroalgae are roughly classified as green, red, or brown algae based on their photosynthetic pigments. Brown algae are considered to be a source of physiologically active substances such as polyphenols. Furthermore, some macroalgae can capture approximately 10 times more carbon dioxide from the atmosphere than terrestrial plants. Therefore, they have immense potential for use in the environment. Recently, macroalgae have emerged as a biomass feedstock for bioethanol production owing to their low lignin content and applicability to biorefinery processes. Herein, we provided an overview of the bioconversion of macroalgae into bioactive substances and biofuels using microbial biotechnology, including engineered yeast designed using molecular display technology.

Cryptococcus: History, Epidemiology and Immune Evasion

Cryptococcosis is a disease caused by the pathogenic fungi Cryptococcus neoformans and Cryptococcus gattii, both environmental fungi that cause severe pneumonia and may even lead to cryptococcal meningoencephalitis. Although C. neoformans affects more fragile individuals, such as immunocompromised hosts through opportunistic infections, C. gattii causes a serious indiscriminate primary infection in immunocompetent individuals. Typically seen in tropical and subtropical environments, C. gattii has increased its endemic area over recent years, largely due to climatic factors that favor contagion in warmer climates. It is important to point out that not only C. gattii, but the Cryptococcus species complex produces a polysaccharidic capsule with immunomodulatory properties, enabling the pathogenic species of Cryptococccus to subvert the host immune response during the establishment of cryptococcosis, facilitating its dissemination in the infected organism. C. gattii causes a more severe and difficult-to-treat infection, with few antifungals eliciting an effective response during chronic treatment. Much of the immunopathology of this cryptococcosis is still poorly understood, with most studies focusing on cryptococcosis caused by the species C. neoformans. C. gattii became more important in the epidemiological scenario with the outbreaks in the Pacific Northwest of the United States, which resulted in phylogenetic studies of the virulent variant responsible for the severe infection in the region. Since then, the study of cryptococcosis caused by C. gattii has helped researchers understand the immunopathological aspects of different variants of this pathogen.

An overview on display systems (phage, bacterial, and yeast display) for production of anticancer antibodies; advantages and disadvantages

Antibodies as ideal therapeutic and diagnostic molecules are among the top-selling drugs providing considerable efficacy in disease treatment, especially in cancer therapy. Limitations of the hybridoma technology as routine antibody generation method in conjunction with numerous developments in molecular biology led to the development of alternative approaches for the streamlined identification of most effective antibodies. In this regard, display selection technologies such as phage display, bacterial display, and yeast display have been widely promoted over the past three decades as ideal alternatives to traditional methods. The display of antibodies on phages is probably the most widespread of these methods, although surface display on bacteria or yeast have been employed successfully, as well. These methods using various sizes of combinatorial antibody libraries and different selection strategies possessing benefits in screening potency, generating, and isolation of high affinity antibodies with low risk of immunogenicity. Knowing the basics of each method assists in the design and retrieval process of antibodies suitable for different diseases, including cancer. In this review, we aim to outline the basics of each library construction and its display method, screening and selection steps. The advantages and disadvantages in comparison to alternative methods, and their applications in antibody engineering will be explained. Finally, we will review approved or non-approved therapeutic antibodies developed by employing these methods, which may serve as therapeutic antibodies in cancer therapy.

Fungal Pathogenesis-Related Cell Wall Biogenesis, with Emphasis on the Maize Anthracnose Fungus Colletotrichum graminicola

The genus Colletotrichum harbors many plant pathogenic species, several of which cause significant yield losses in the field and post harvest. Typically, in order to infect their host plants, spores germinate, differentiate a pressurized infection cell, and display a hemibiotrophic lifestyle after plant invasion. Several factors required for virulence or pathogenicity have been identified in different Colletotrichum species, and adaptation of cell wall biogenesis to distinct stages of pathogenesis has been identified as a major pre-requisite for the establishment of a compatible parasitic fungus-plant interaction. Here, we highlight aspects of fungal cell wall biogenesis during plant infection, with emphasis on the maize leaf anthracnose and stalk rot fungus, Colletotrichum graminicola.

Overexpression of cell-wall GPI-anchored proteins restores cell growth of N-glycosylation-defective och1 mutants in Schizosaccharomyces pombe

The glycoproteins of yeast contain a large outer chain on N-linked oligosaccharides; therefore, yeast is not suitable for producing therapeutic glycoproteins for human use. Using a deletion mutant strain of α1,6-mannosyltransferase (och1Δ), we previously produced humanized N-glycans in fission yeast; however, the Schizosaccharomyces pombe och1Δ cells displayed a growth delay even during vegetative growth, resulting in reduced productivity of heterologous proteins. To overcome this problem, here we performed a genome-wide screen for genes that would suppress the growth defect of temperature-sensitive och1Δ cells. Using a genomic library coupled with screening of 18,000 transformants, we identified two genes (pwp1⁺, SPBC1E8.05), both encoding GPI-anchored proteins, that increased the growth rate of och1Δ cells, lacking the outer chain. We further showed that a high copy number of the genes was needed to improve the growth rate. Mutational analysis of Pwp1p revealed that the GPI-anchored region of Pwp1p is important in attenuating the growth defect. Analysis of disruptants of pwp1⁺ and SPBC1E8.05 showed that neither gene was essential for cell viability; however, both mutants were sensitive β-glucanase, suggesting that Pwp1p and the protein encoded by SPBC1E8.05 non-enzymatically support β-glucan on the cell-surface of S. pombe. Collectively, our work not only sheds light on the functional relationships between GPI-anchored proteins and N-linked oligosaccharides of glycoproteins in S. pombe, but also supports the application of S. pombe to the production of human glycoprotein. KEY POINTS: • We screened for genes that suppress the growth defect of fission yeast och1Δ cells. • Appropriate expression of GPI-anchored proteins alleviates the growth delay of och1Δ cells. • The GPI-anchor domain of Pwp1p is important for suppressing the growth defect of och1Δ cells.

The dual role of amyloid-β-sheet sequences in the cell surface properties of FLO11-encoded flocculins in Saccharomyces cerevisiae

Fungal adhesins (Als) or flocculins are family of cell surface proteins that mediate adhesion to diverse biotic and abiotic surfaces. A striking characteristic of Als proteins originally identified in the pathogenic Candida albicans is to form functional amyloids that mediate cis-interaction leading to the formation of adhesin nanodomains and trans-interaction between amyloid sequences of opposing cells. In this report, we show that flocculins encoded by FLO11 in Saccharomyces cerevisiae behave like adhesins in C. albicans. To do so, we show that the formation of nanodomains under an external physical force requires a threshold number of amyloid-forming sequences in the Flo11 protein. Then, using a genome editing approach, we constructed strains expressing variants of the Flo11 protein under the endogenous FLO11 promoter, leading to the demonstration that the loss of amyloid-forming sequences strongly reduces cell-cell interaction but has no effect on either plastic adherence or invasive growth in agar, both phenotypes being dependent on the N- and C-terminal ends of Flo11p. Finally, we show that the location of Flo11 is not altered either by the absence of amyloid-forming sequences or by the removal of the N- or C-terminus of the protein.

Diversity of GPI-anchored fungal adhesins

Selective adhesion of fungal cells to one another and to foreign surfaces is fundamental for the development of multicellular growth forms and the successful colonization of substrates and host organisms. Accordingly, fungi possess diverse cell wall-associated adhesins, mostly large glycoproteins, which present N-terminal adhesion domains at the cell surface for ligand recognition and binding. In order to function as robust adhesins, these glycoproteins must be covalently linkedto the cell wall via C-terminal glycosylphosphatidylinositol (GPI) anchors by transglycosylation. In this review, we summarize the current knowledge on the structural and functional diversity of so far characterized protein families of adhesion domains and set it into a broad context by an in-depth bioinformatics analysis using sequence similarity networks. In addition, we discuss possible mechanisms for the membrane-to-cell wall transfer of fungal adhesins by membrane-anchored Dfg5 transglycosidases.

Compromised chitin synthesis in lager yeast affects its Congo red resistance and release of mannoproteins from the cells

A mutant lager strain resistant to the cell wall-perturbing agent Congo red (CR) was isolated and the genetic alterations underlying CR resistance were investigated by whole genome sequencing. The parental lager strain was found to contain three distinct Saccharomyces cerevisiae (Sc)-type CHS6 (CHitin Synthase-related 6) alleles, two of which have one or two nonsense mutations in the open reading frame, leaving only one functional allele, whereas the functional allele was missing in the isolated CR-resistant strain. On the other hand, the Saccharomyces eubayanus-type CHS6 alleles shared by both the parental and mutant strains appeared to contribute poorly to chitin synthase-activating function. Therefore, the CR resistance of the mutant strain was attributable to the overall compromised activity of CHS6 gene products. The CR-resistant mutant cells exhibited less chitin production on the cell surface and smaller amounts of mannoprotein release into the medium. All these traits, in addition to the CR resistance, were complemented by the functional ScCHS6 gene. It is of great interest whether the frequent nonsense mutations found in ScCHS6 open reading frame in lager yeast strains are a consequence of the domestication process of lager yeast.

A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced α-glucan or galactomannan

Chitin is an important fungal cell wall component that is cross-linked to β-glucan for structural integrity. Acquisition of chitin to glucan cross-links has previously been shown to be performed by transglycosylation enzymes in Saccharomyces cerevisiae, called Congo Red hypersensitive (Crh) enzymes. Here, we characterized the impact of deleting all seven members of the crh gene family (crhA-G) in Aspergillus niger on cell wall integrity, cell wall composition and genome-wide gene expression. In this study, we show that the seven-fold crh knockout strain shows slightly compact growth on plates, but no increased sensitivity to cell wall perturbing compounds. Additionally, we found that the cell wall composition of this knockout strain was virtually identical to that of the wild type. In congruence with these data, genome-wide expression analysis revealed very limited changes in gene expression and no signs of activation of the cell wall integrity response pathway. However, deleting the entire crh gene family in cell wall mutants that are deficient in either galactofuranose or α-glucan, mainly α-1,3-glucan, resulted in a synthetic growth defect and an increased sensitivity towards Congo Red compared to the parental strains, respectively. Altogether, these results indicate that loss of the crh gene family in A. niger does not trigger the cell wall integrity response, but does play an important role in ensuring cell wall integrity in mutant strains with reduced galactofuranose or α-glucan.

Structural base for the transfer of GPI-anchored glycoproteins into fungal cell walls

The correct distribution and trafficking of proteins are essential for all organisms. Eukaryotes evolved a sophisticated trafficking system which allows proteins to reach their destination within highly compartmentalized cells. One eukaryotic hallmark is the attachment of a glycosylphosphatidylinositol (GPI) anchor to C-terminal ω-peptides, which are used as a zip code to guide a subset of membrane-anchored proteins through the secretory pathway to the plasma membrane. In fungi, the final destination of many GPI-anchored proteins is their outermost compartment, the cell wall. Enzymes of the Dfg5 subfamily catalyze the essential transfer of GPI-anchored substrates from the plasma membrane to the cell wall and discriminate between plasma membrane-resident GPI-anchored proteins and those transferred to the cell wall (GPI-CWP). We solved the structure of Dfg5 from a filamentous fungus and used in crystallo glycan fragment screening to reassemble the GPI-core glycan in a U-shaped conformation within its binding pocket. The resulting model of the membrane-bound Dfg5•GPI-CWP complex is validated by molecular dynamics (MD) simulations and in vivo mutants in yeast. The latter show that impaired transfer of GPI-CWPs causes distorted cell-wall integrity as indicated by increased chitin levels. The structure of a Dfg5•β1,3-glycoside complex predicts transfer of GPI-CWP toward the nonreducing ends of acceptor glycans in the cell wall. In addition to our molecular model for Dfg5-mediated transglycosylation, we provide a rationale for how GPI-CWPs are specifically sorted toward the cell wall by using GPI-core glycan modifications.

Pathways of heme utilization in fungi

Iron acquisition is challenging in most environments. As an alternative to elemental iron, organisms can take up iron-protoporphyrin IX, or heme. Heme can be found in decaying organic matter and is particularly prevalent in animal hosts. Fungi have evolved at least three distinct endocytosis-mediated heme uptake systems, which have been studied in detail in the organisms Candida albicans, Cryptococcus neoformans and Schizosaccharomyces pombe. Here we summarize the known molecular details of these three uptake systems that enable parasitic and saprophytic fungi to take advantage of external heme as either cellular iron or heme sources.

The covalent SNAP tag for protein display quantification and low-pH protein engineering

Yeast display has become an important tool for modern biotechnology with many advantages for eukaryotic protein engineering. Antibody-based peptide interactions are often used to quantify yeast surface expression (e.g., by fusing a target protein to a FLAG, Myc, polyhistidine, or other peptide tag). However, antibody-antigen interactions require high stability for accurate quantification, and conventional tag systems based on such interactions may not be compatible with a low pH environment. In this study, a SNAP tag was introduced to a yeast display platform to circumvent disadvantages of conventional antibody display tags at low pH. SNAP forms a covalent bond with its small-molecule substrate, enabling precise and pH-independent protein display tagging. We compared the SNAP tag to conventional antibody-based peptide fusion and to direct fluorescent domain fusion using antibody fragment crystallizable (Fc) gene libraries as a case study in low pH protein engineering. Our results demonstrated that covalent SNAP tags can effectively quantify protein-surface expression at low pH, enabling the enrichment of Fc variants with increased affinity at pH 6.0 to the neonatal Fc receptor (FcRn). Incorporation of a covalent SNAP tag thus overcomes disadvantages of conventional antibody-based expression tags and enables protein-engineering applications outside of physiological pH.

The Genetics and Biochemistry of Cell Wall Structure and Synthesis in Neurospora crassa, a Model Filamentous Fungus

This review discusses the wealth of information available for the N. crassa cell wall. The basic organization and structure of the cell wall is presented and how the wall changes during the N. crassa life cycle is discussed. Over forty cell wall glycoproteins have been identified by proteomic analyses. Genetic and biochemical studies have identified many of the key enzymes needed for cell wall biogenesis, and the roles these enzymes play in cell wall biogenesis are discussed. The review includes a discussion of how the major cell wall components (chitin, β-1,3-glucan, mixed β-1,3-/ β-1,4- glucans, glycoproteins, and melanin) are synthesized and incorporated into the cell wall. We present a four-step model for how cell wall glycoproteins are covalently incorporated into the cell wall. In N. crassa, the covalent incorporation of cell wall glycoproteins into the wall occurs through a glycosidic linkage between lichenin (a mixed β-1,3-/β-1,4- glucan) and a "processed" galactomannan that has been attached to the glycoprotein N-linked oligosaccharides. The first step is the addition of the galactomannan to the N-linked oligosaccharide. Mutants affected in galactomannan formation are unable to incorporate glycoproteins into their cell walls. The second step is carried out by the enzymes from the GH76 family of α-1,6-mannanases, which cleave the galactomannan to generate a processed galactomannan. The model suggests that the third and fourth steps are carried out by members of the GH72 family of glucanosyltransferases. In the third step the glucanosyltransferases cleave lichenin and generate enzyme/substrate intermediates in which the lichenin is covalently attached to the active site of the glucanosyltransferases. In the final step, the glucanosyltransferases attach the lichenin onto the processed galactomannans, which creates new glycosidic bonds and effectively incorporates the glycoproteins into the cross-linked cell wall glucan/chitin matrix.

Cell surface display of proteins on filamentous fungi

Protein display approaches have been useful to endow the cell surface of yeasts with new catalytic activities so that they can act as enhanced whole-cell biocatalysts. Despite their biotechnological potential, protein display technologies remain poorly developed for filamentous fungi. The lignocellulolytic character of some of them coupled to the cell surface biosynthesis of valuable molecules by a single or a cascade of several displayed enzymes is an appealing prospect. Cell surface protein display consists in the co-translational fusion of a functional protein (passenger) to an anchor one, usually a cell-wall-resident protein. The abundance, spacing, and local environment of the displayed enzymes-determined by the relationship of the anchor protein with the structure and dynamics of the engineered cell wall-are factors that influence the performance of display-based biocatalysts. The development of protein display strategies in filamentous fungi could be based on the field advances in yeasts; however, the unique composition, structure, and biology of filamentous fungi cell walls require the customization of the approach to those microorganisms. In this prospective review, the cellular bases, the design principles, and the available tools to foster the development of cell surface protein display technologies in filamentous fungi are discussed.

Targeting the fungal cell wall: current therapies and implications for development of alternative antifungal agents

Fungal infections are a worldwide problem associated with high morbidity and mortality. There are relatively few antifungal agents, and resistance has emerged within these pathogens for the newest antifungal drugs. As the fungal cell wall is critical for growth and development, it is one of the most important targets for drug development. In this review, the currently available cell wall inhibitors and suitable drug candidates for the treatment of fungal infections are explored. Future studies of the fungal cell wall and compounds that have detrimental effects on this important outer structural layer could aid in antifungal drug discovery and lead to the development of alternative cell wall inhibitors to fill gaps in clinical therapies for difficult-to-treat fungal infections.

The fungal cell wall as a target for the development of new antifungal therapies

In the past three decades invasive mycoses have globally emerged as a persistent source of healthcare-associated infections. The cell wall surrounding the fungal cell opposes the turgor pressure that otherwise could produce cell lysis. Thus, the cell wall is essential for maintaining fungal cell shape and integrity. Given that this structure is absent in host mammalian cells, it stands as an important target when developing selective compounds for the treatment of fungal infections. Consequently, treatment with echinocandins, a family of antifungal agents that specifically inhibits the biosynthesis of cell wall (1-3)β-D-glucan, has been established as an alternative and effective antifungal therapy. However, the existence of many pathogenic fungi resistant to single or multiple antifungal families, together with the limited arsenal of available antifungal compounds, critically affects the effectiveness of treatments against these life-threatening infections. Thus, new antifungal therapies are required. Here we review the fungal cell wall and its relevance in biotechnology as a target for the development of new antifungal compounds, disclosing the most promising cell wall inhibitors that are currently in experimental or clinical development for the treatment of some invasive mycoses.

Going with the Flo: The Role of Flo11-Dependent and Independent Interactions in Yeast Mat Formation

Strains of the bakers’ yeast Saccharomyces cerevisiae that are able to generate a multicellular structure called a mat on low percentage (0.3%) agar plates are given a selective advantage over strains that cannot exhibit this phenotype. This environment may exhibit some similarities to the rotting fruit on which S. cerevisiae often grows in nature. Mat formation occurs when the cells spread over the plate as they grow, and cells in the center of the biofilm aggregate to form multicellular structures that resemble a floral pattern. This multicellular behavior is dependent on the cell surface flocculin Flo11. This review covers recent information on the structure of Flo11 and how this likely impacts mat formation as well as how variegated expression of Flo11 influences mat formation. Finally, it also discusses several Flo11-independent genetic factors that control mat formation, such as vacuolar protein sorting (VPS) genes, cell wall signaling components, and heat shock proteins.

Biochemical Characterization of Recombinant Thermostable Cohnella sp. A01 β-Glucanase

Background

Typically, non-cellulytic glucanase, including fungi and yeast cell wall hydrolyzing enzymes, are released by some symbiotic fungi and plants during the mycoparasitic fungi attack on plants. These enzymes are known as the defense mechanisms of plants. This study intends to investigate the biochemical properties of β-1,6-glucanase (bg16M) from native thermophilic bacteria, Cohnella A01.

Methods

bg16M gene was cloned and expressed in E. coli BL21 (DE3). The enzyme was purified utilizing Ni-NTA nikcle sepharose column. Pustulan and laminarin were selected as substrates in enzyme assay. The purified bg16M enzyme was treated with different pH, temperature, metal ions, and detergents.

Results

The expressed protein, including 639 amino acids, showed a high similarity with the hydrolytic glycosylated family 30. The molecular weight of enzyme was 64 kDa, and purification yield was 46%. The bg16M demonstrated activity as 4.83 U/ml on laminarin and 2.88 U/ml on pustulan. The optimum pH and temperature of the enzyme were 8 and 50 °C, respectively. The enzyme had an appropriate stability at high temperatures and in the pH range of 7 to 9, showing acceptable stability, while it did not lose enzymatic activity completely at acidic or basic pH. None of the studied metal ions and chemical compounds was the activator of bg16M, and urea, SDS, and copper acted as enzyme inhibitors.

Conclusion

Biochemical characterization of this enzyme revealed that bg16M can be applied in beverage industries and medical sectors because of its high activity, as well as thermal and alkaline stability.

Amyloid-Like β-Aggregates as Force-Sensitive Switches in Fungal Biofilms and Infections

Cellular aggregation is an essential step in the formation of biofilms, which promote fungal survival and persistence in hosts. In many of the known yeast cell adhesion proteins, there are amino acid sequences predicted to form amyloid-like β-aggregates. These sequences mediate amyloid formation in vitro. In vivo, these sequences mediate a phase transition from a disordered state to a partially ordered state to create patches of adhesins on the cell surface. These β-aggregated protein patches are called adhesin nanodomains, and their presence greatly increases and strengthens cell-cell interactions in fungal cell aggregation. Nanodomain formation is slow (with molecular response in minutes and the consequences being evident for hours), and strong interactions lead to enhanced biofilm formation. Unique among functional amyloids, fungal adhesin β-aggregation can be triggered by the application of physical shear force, leading to cellular responses to flow-induced stress and the formation of robust biofilms that persist under flow. Bioinformatics analysis suggests that this phenomenon may be widespread. Analysis of fungal abscesses shows the presence of surface amyloids in situ, a finding which supports the idea that phase changes to an amyloid-like state occur in vivo. The amyloid-coated fungi bind the damage-associated molecular pattern receptor serum amyloid P component, and there may be a consequential modulation of innate immune responses to the fungi. Structural data now suggest mechanisms for the force-mediated induction of the phase change. We summarize and discuss evidence that the sequences function as triggers for protein aggregation and subsequent cellular aggregation, both in vitro and in vivo.

β-1,6-glucan synthesis-associated genes are required for proper spore wall formation in Saccharomyces cerevisiae

The yeast spore wall is an excellent model to study the assembly of an extracellular macromolecule structure. In the present study, mutants defective in β-1,6-glucan synthesis, including kre1∆, kre6∆, kre9∆ and big1∆, were sporulated to analyse the effect of β-1,6-glucan defects on the spore wall. Except for kre6∆, these mutant spores were sensitive to treatment with ether, suggesting that the mutations perturb the integrity of the spore wall. Morphologically, the mutant spores were indistinguishable from wild-type spores. They lacked significant sporulation defects partly because the chitosan layer, which covers the glucan layer, compensated for the damage. The proof for this model was obtained from the effect of the additional deletion of CHS3 that resulted in the absence of the chitosan layer. Among the double mutants, the most severe spore wall deficiency was observed in big1∆ spores. The majority of the big1∆chs3∆ mutants failed to form visible spores at a higher temperature. Given that the big1∆ mutation caused a failure to attach a GPI-anchored reporter, Cwp2-GFP, to the spore wall, β-1,6-glucan is involved in tethering of GPI-anchored proteins in the spore wall as well as in the vegetative cell wall. Thus, β-1,6-glucan is required for proper organization of the spore wall. Copyright © 2017 John Wiley & Sons, Ltd.

Accurate analysis of fusion expression of Pichia pastoris glycosylphosphatidylinositol-modified cell wall proteins

Glycosylphosphatidylinositol (GPI)-anchored glycoproteins have diverse intrinsic functions in yeasts, and they also have different uses in vitro. The GPI-modified cell wall proteins GCW21, GCW51, and GCW61 of Pichia pastoris were chosen as anchoring proteins to construct co-expression strains in P. pastoris GS115. The hydrolytic activity and the amount of Candida antarctica lipase B (CALB) displayed on cell surface increased significantly following optimization of the fusion gene dosage and combination of the homogeneous or heterogeneous cell wall proteins. Maximum CALB hydrolytic activity was achieved at 4920 U/g dry cell weight in strain GS115/CALB-GCW (51 + 51 + 61 + 61) after 120 h of methanol induction. Changes in structural morphology and the properties of the cell surfaces caused by co-expression of fusion proteins were observed by transmission electron microscopy (TEM) and on plates containing cell-wall-destabilizing reagent. Our results suggested that both the outer and inner cell layers were significantly altered by overexpression of GPI-modified cell wall proteins. Interestingly, quantitative analysis of the inner layer components showed an increase in β-1,3-glucan, but no obvious changes in chitin in the strains overexpressing GPI-modified cell wall proteins.

Mapping of endoglucanases displayed on yeast cell surface using atomic force microscopy

The surface of yeast cells has been an attractive interface for the effective use of cellulose. Surface enzymes, however, are difficult to visualize and evaluate. In this study, two kinds of unique anchoring regions were used to display the cellulase, endoglucanase (EG), on a yeast cell surface. Differences in the display level and the localization of EG were observed by atomic force microscopy. By surveying the yeast cell surface with a chemically modified cantilever, the interactive force between the cellulose and EG was measured. Force curve mapping revealed differences in the display levels and the localization of EG according to anchoring regions. The proposed methodology enables visualization of displayed enzymes such as EG on the yeast cell surface.

Geometry and expression enhance enrichment of functional yeast-displayed ligands via cell panning

Yeast surface display has proven to be an effective tool in the discovery and evolution of ligands with new or improved binding activity. Selections for binding activity are generally carried out using immobilized or fluorescently labeled soluble domains of target molecules such as recombinant ectodomain fragments. While this method typically provides ligands with high affinity and specificity for the soluble molecular target, translation to binding true membrane-bound cellular target is commonly problematic. Direct selections against mammalian cell surfaces can be carried out either exclusively or in combination with soluble target-based selections to further direct towards ligands for genuine cellular target. Using a series of fibronectin domain, affibody, and Gp2 ligands and human cell lines expressing a range of their targets, epidermal growth factor receptor and carcinoembryonic antigen, this study quantitatively identifies the elements that dictate ligand enrichment and yield. Most notably, extended flexible linkers between ligand and yeast enhance enrichment ratios from 1.4 ± 0.8 to 62 ± 57 for a low-affinity (>600 nM) binder on cells with high target expression and from 14 ± 13 to 74 ± 25 for a high-affinity binder (2 nM) on cells with medium valency. Inversion of the yeast display fusion from C-terminal display to N-terminal display still enables enrichment albeit with 40-97% reduced efficacy. Collectively, this study further enlightens the conditions-while highlighting new approaches-that yield successful enrichment of yeast-displayed binding ligands via panning on mammalian cells. Biotechnol. Bioeng. 2016;113: 2328-2341. © 2016 Wiley Periodicals, Inc.

Oxygen-independent FbFP: Fluorescent sentinel and oxygen sensor component in Saccharomyces cerevisiae and Candida albicans

FMN-binding fluorescent proteins (FbFPs) outperform GFP and its derivatives because of their oxygen-independence, small size and rapid maturation. FbFPs have been used successfully as reliable reporters of gene expression in the cytoplasm of pro- and eukaryotes. Here we extend previous findings on the codon-adapted CaFbFP variant, which functions in the apathogenic yeast Saccharomyces cerevisiae and the human fungal pathogen Candida albicans. In both fungal species, CaFbFP could be targeted to the nucleus and the cell wall by endogenous signals (H2B-/Aga2-fusions) demonstrating its use as a fluorescent beacon in these relevant cellular locations. Transformants of both fungal species producing a CaFbFP-YFP fusion (YFOS) showed variable energy transfer from CaFbFP to YFP (FRET) that depended in its extent on external O2 concentrations. Applications as fluorescent sentinel and oxygen biosensor expand the FbFP toolbox to study oxygen-independent cellular processes under hypoxia.

The N-Linked Outer Chain Mannans and the Dfg5p and Dcw1p Endo-α-1,6-Mannanases Are Needed for Incorporation of Candida albicans Glycoproteins into the Cell Wall

A biochemical pathway for the incorporation of cell wall protein into the cell wall of Neurospora crassa was recently proposed. In this pathway, the DFG-5 and DCW-1 endo-α-1,6-mannanases function to covalently cross-link cell wall protein-associated N-linked galactomannans, which are structurally related to the yeast outer chain mannans, into the cell wall glucan-chitin matrix. In this report, we demonstrate that the mannosyltransferase enzyme Och1p, which is needed for the synthesis of the N-linked outer chain mannan, is essential for the incorporation of cell wall glycoproteins into the Candida albicans cell wall. Using endoglycosidases, we show that C. albicans cell wall proteins are cross-linked into the cell wall via their N-linked outer chain mannans. We further demonstrate that the Dfg5p and Dcw1p α-1,6-mannanases are needed for the incorporation of cell wall glycoproteins into the C. albicans cell wall. Our results support the hypothesis that the Dfg5p and Dcw1p α-1,6-mannanases incorporate cell wall glycoproteins into the C. albicans cell wall by cross-linking outer chain mannans into the cell wall glucan-chitin matrix.

Cell-surface display of enzymes by the yeast Saccharomyces cerevisiae for synthetic biology

In yeast cell-surface displays, functional proteins, such as cellulases, are genetically fused to an anchor protein and expressed on the cell surface. Saccharomyces cerevisiae, which is often utilized as a cell factory for the production of fuels, chemicals, and proteins, is the most commonly used yeast for cell-surface display. To construct yeast cells with a desired function, such as the ability to utilize cellulose as a substrate for bioethanol production, cell-surface display techniques for the efficient expression of enzymes on the cell membrane need to be combined with metabolic engineering approaches for manipulating target pathways within cells. In this Minireview, we summarize the recent progress of biorefinery fields in the development and application of yeast cell-surface displays from a synthetic biology perspective and discuss approaches for further enhancing cell-surface display efficiency.

Applications of Yeast Surface Display for Protein Engineering

The method of displaying recombinant proteins on the surface of Saccharomyces cerevisiae via genetic fusion to an abundant cell wall protein, a technology known as yeast surface display, or simply, yeast display, has become a valuable protein engineering tool for a broad spectrum of biotechnology and biomedical applications. This review focuses on the use of yeast display for engineering protein affinity, stability, and enzymatic activity. Strategies and examples for each protein engineering goal are discussed. Additional applications of yeast display are also briefly presented, including protein epitope mapping, identification of protein-protein interactions, and uses of displayed proteins in industry and medicine.

The importance of connections between the cell wall integrity pathway and the unfolded protein response in filamentous fungi

In the external environment, or within a host organism, filamentous fungi experience sudden changes in nutrient availability, osmolality, pH, temperature and the exposure to toxic compounds. The fungal cell wall represents the first line of defense, while also performing essential roles in morphology, development and virulence. A polarized secretion system is paramount for cell wall biosynthesis, filamentous growth, nutrient acquisition and interactions with the environment. The unique ability of filamentous fungi to secrete has resulted in their industrial adoption as fungal cell factories. Protein maturation and secretion commences in the endoplasmic reticulum (ER). The unfolded protein response (UPR) maintains ER functionality during exposure to secretion and cell wall stress. UPR, therefore, influences secretion and cell wall homeostasis, which in turn impacts upon numerous fungal traits important to pathogenesis and biotechnology. Subsequently, this review describes the relevance of the cell wall and UPR systems to filamentous fungal pathogens or industrial microbes and then highlights interconnections between the two systems. Ultimately, the possible biotechnological applications of an enhanced understanding of such regulatory systems in combating fungal disease, or the removal of natural bottlenecks in protein secretion in an industrial setting, are discussed.

The Neurospora crassa CPS-1 polysaccharide synthase functions in cell wall biosynthesis

The Neurospora crassa cps-1 gene encodes a polysaccharide synthase with homology to the Cryptococcus neoformans hyaluronic acid synthase Cps1p. Homologs of the cps-1 gene are found in the genomes of many fungi. Loss of CPS-1 results in a cell wall defect that affects all stages of the N. crassa life cycle, including vegetative growth, protoperithecia (female mating structure) development, and conidia (asexual spore) development. The cell wall of cps-1 deletion mutants is sensitive to cell wall perturbation reagents. Our results demonstrate that CPS-1 is required for the incorporation of cell wall proteins into the cell wall and plays a critical role in cell wall biogenesis. We found that the N. crassa cell wall is devoid of hyaluronic acid, and conclude that the polysaccharide produced by the CPS-1 is not hyaluronic acid.

Neurospora crassa 1,3-α-glucan synthase, AGS-1, is required for cell wall biosynthesis during macroconidia development

The Neurospora crassa genome encodes two 1,3-α-glucan synthases. One of these 1,3-α-glucan synthase genes, ags-1, was shown to be required for the synthesis of 1,3-α-glucan in the aerial hyphae and macroconidia cell walls. 1,3-α-Glucan was found in the conidia cell wall, but was absent from the vegetative hyphae cell wall. Deletion of ags-1 affected conidial development. Δags-1 produced only 5 % as many conidia as the WT and most of the conidia produced by Δags-1 were not viable. The ags-1 upstream regulatory elements were shown to direct cell-type-specific expression of red fluorescent protein in conidia and aerial hyphae. A haemagglutinin-tagged AGS-1 was found to be expressed in aerial hyphae and conidia. The research showed that 1,3-α-glucan is an aerial hyphae and conidia cell wall component, and is required for normal conidial differentiation.

A novel lily anther-specific gene encodes adhesin-like proteins associated with exine formation during anther development

The anther-specific gene LLA1271 isolated from lily (Lilium longiflorum Thunb.) anthers is novel and exists in two forms. The protein encoded by LLA1271 may represent an adhesin-like protein first found in higher plants. The protein contains a typical N-terminal signal peptide followed by a highly conserved repeat domain. The LLA1271 gene is temporally expressed at the phase of microspore development. RNA blot and RNA in situ hybridization analyses demonstrated that the gene was expressed both in the tapetum and in the microspore. The gene is endo- and exogenously induced by gibberellin. Studies with the gibberellin biosynthesis inhibitor uniconazole and an inhibitor of ethylene activity, 2,5-norbornadien (NBD), revealed that LLA1271 is negatively regulated by ethylene, and a cross-talk of regulation between gibberellin and ethylene occurs in young anthers. The treatment with NBD caused the tapetum to become densely cytoplasmic and highly polarized, whereas uniconazole arrested tapetal development in a state close to that of a tapetum without treatment. The LLA1271 protein is heat stable and heterogeneous. An immunoblot of separated protein fractions of the anther revealed that the LLA1271 protein was detected in protein fraction of the microspore released from the cell wall by treatment with either 0.5% or 2% Triton X-100. Ectopic expression of LLA1271 resulted in impaired stamen and low pollen germination. Scanning electron microscopy of TAP::LLA1271 pollen showed distorted exine formation and patterning. The LLA1271 protein once synthesized in both the tapetum and microspore is secreted and deposited on the surface of microspores, moderately affecting exine formation and patterning.

Engineering microbial surfaces to degrade lignocellulosic biomass

Renewable lignocellulosic plant biomass is a promising feedstock from which to produce biofuels, chemicals, and materials. One approach to cost-effectively exploit this resource is to use consolidating bioprocessing (CBP) microbes that directly convert lignocellulose into valuable end products. Because many promising CBP-enabling microbes are non-cellulolytic, recent work has sought to engineer them to display multi-cellulase containing minicellulosomes that hydrolyze biomass more efficiently than isolated enzymes. In this review, we discuss progress in engineering the surfaces of the model microorganisms: Bacillus subtilis, Escherichia coli, and Saccharomyces cerevisiae. We compare the distinct approaches used to display cellulases and minicellulosomes, as well as their surface enzyme densities and cellulolytic activities. Thus far, minicellulosomes have only been grafted onto the surfaces of B. subtilis and S. cerevisiae, suggesting that the absence of an outer membrane in fungi and Gram-positive bacteria may make their surfaces better suited for displaying the elaborate multi-enzyme complexes needed to efficiently degrade lignocellulose.

Identification of genes upregulated by the transcription factor Bcr1 that are involved in impermeability, impenetrability, and drug resistance of Candida albicans a/α biofilms

Candida albicans forms two types of biofilm, depending upon the configuration of the mating type locus. Although architecturally similar, a/α biofilms are impermeable, impenetrable, and drug resistant, whereas a/a and α/α biofilms lack these traits. The difference appears to be the result of an alternative matrix. Overexpression in a/a cells of BCR1, a master regulator of the a/α matrix, conferred impermeability, impenetrability, and drug resistance to a/a biofilms. Deletion of BCR1 in a/α cells resulted in the loss of these a/α-specific biofilm traits. Using BCR1 overexpression in a/a cells, we screened 107 genes of interest and identified 8 that were upregulated by Bcr1. When each was overexpressed in a/a biofilms, the three a/α traits were partially conferred, and when each was deleted in a/α cells, the traits were partially lost. Five of the eight genes have been implicated in iron homeostasis, and six encode proteins that are either in the wall or plasma membrane or secreted. All six possess sites for O-linked and N-linked glycosylation that, like glycosylphosphatidylinositol (GPI) anchors, can cross-link to the wall and matrix, suggesting that they may exert a structural role in conferring impermeability, impenetrability, and drug resistance, in addition to their physiological functions. The fact that in a screen of 107 genes, all 8 of the Bcr1-upregulated genes identified play a role in impermeability, impenetrability, and drug resistance suggests that the formation of the a/α matrix is highly complex and involves a larger number of genes than the initial ones identified here.

Fungal cell wall organization and biosynthesis

The composition and organization of the cell walls from Saccharomyces cerevisiae, Candida albicans, Aspergillus fumigatus, Schizosaccharomyces pombe, Neurospora crassa, and Cryptococcus neoformans are compared and contrasted. These cell walls contain chitin, chitosan, β-1,3-glucan, β-1,6-glucan, mixed β-1,3-/β-1,4-glucan, α-1,3-glucan, melanin, and glycoproteins as major constituents. A comparison of these cell walls shows that there is a great deal of variability in fungal cell wall composition and organization. However, in all cases, the cell wall components are cross-linked together to generate a cell wall matrix. The biosynthesis and properties of each of the major cell wall components are discussed. The chitin and glucans are synthesized and extruded into the cell wall space by plasma membrane-associated chitin synthases and glucan synthases. The glycoproteins are synthesized by ER-associated ribosomes and pass through the canonical secretory pathway. Over half of the major cell wall proteins are modified by the addition of a glycosylphosphatidylinositol anchor. The cell wall glycoproteins are also modified by the addition of O-linked oligosaccharides, and their N-linked oligosaccharides are extensively modified during their passage through the secretory pathway. These cell wall glycoprotein posttranslational modifications are essential for cross-linking the proteins into the cell wall matrix. Cross-linking the cell wall components together is essential for cell wall integrity. The activities of four groups of cross-linking enzymes are discussed. Cell wall proteins function as cross-linking enzymes, structural elements, adhesins, and environmental stress sensors and protect the cell from environmental changes.

Architecture and biosynthesis of the Saccharomyces cerevisiae cell wall

The wall gives a Saccharomyces cerevisiae cell its osmotic integrity; defines cell shape during budding growth, mating, sporulation, and pseudohypha formation; and presents adhesive glycoproteins to other yeast cells. The wall consists of β1,3- and β1,6-glucans, a small amount of chitin, and many different proteins that may bear N- and O-linked glycans and a glycolipid anchor. These components become cross-linked in various ways to form higher-order complexes. Wall composition and degree of cross-linking vary during growth and development and change in response to cell wall stress. This article reviews wall biogenesis in vegetative cells, covering the structure of wall components and how they are cross-linked; the biosynthesis of N- and O-linked glycans, glycosylphosphatidylinositol membrane anchors, β1,3- and β1,6-linked glucans, and chitin; the reactions that cross-link wall components; and the possible functions of enzymatic and nonenzymatic cell wall proteins.

The Neurospora crassa dfg5 and dcw1 genes encode α-1,6-mannanases that function in the incorporation of glycoproteins into the cell wall

The covalent cross-linking of cell wall proteins into the cell wall glucan/chitin matrix is an important step in the biogenesis of the fungal cell wall. We demonstrate that the Neurospora crassa DFG5 (NCU03770) and DCW1 (NCU08127) enzymes function in vivo to cross-link glycoproteins into the cell wall. Mutants lacking DFG5 or DCW1 release slightly elevated levels of cell wall proteins into their growth medium. Mutants lacking both DFG5 and DCW1 have substantially reduced levels of cell wall proteins in their cell walls and release large amounts of known cell wall proteins into the medium. DFG5 and DCW1 are members of the GH76 family of glycosyl hydrolases, which have specificity to recognize and cleave α-1,6-mannans. A model for incorporation of glycoproteins into the cell wall through the α-1,6-mannan core of the N-linked galactomannan is presented. In this model, DFG5 and DCW1 recognize the N-linked galactomannan present on glycoproteins and cross-link it into the cell wall glucan/chitin matrix.

New insights into the structure of (1→3,1→6)-β-D-glucan side chains in the Candida glabrata cell wall

β-Glucan is a (1→3)-β-linked glucose polymer with (1→6)-β-linked side chains and a major component of fungal cell walls. β-Glucans provide structural integrity to the fungal cell wall. The nature of the (1-6)-β-linked side chain structure of fungal (1→3,1→6)-β-D-glucans has been very difficult to elucidate. Herein, we report the first detailed structural characterization of the (1→6)-β-linked side chains of Candida glabrata using high-field NMR. The (1→6)-β-linked side chains have an average length of 4 to 5 repeat units spaced every 21 repeat units along the (1→3)-linked polymer backbone. Computer modeling suggests that the side chains have a bent curve structure that allows for a flexible interconnection with parallel (1→3)-β-D-glucan polymers, and/or as a point of attachment for proteins. Based on these observations we propose new approaches to how (1→6)-β-linked side chains interconnect with neighboring glucan polymers in a manner that maximizes fungal cell wall strength, while also allowing for flexibility, or plasticity.

Choosing the right lifestyle: adhesion and development in Saccharomyces cerevisiae

The budding yeast Saccharomyces cerevisiae is a eukaryotic microorganism that is able to choose between different unicellular and multicellular lifestyles. The potential of individual yeast cells to switch between different growth modes is advantageous for optimal dissemination, protection and substrate colonization at the population level. A crucial step in lifestyle adaptation is the control of self- and foreign adhesion. For this purpose, S. cerevisiae contains a set of cell wall-associated proteins, which confer adhesion to diverse biotic and abiotic surfaces. Here, we provide an overview of different aspects of S. cerevisiae adhesion, including a detailed description of known lifestyles, recent insights into adhesin structure and function and an outline of the complex regulatory network for adhesin gene regulation. Our review shows that S. cerevisiae is a model system suitable for studying not only the mechanisms and regulation of cell adhesion, but also the role of this process in microbial development, ecology and evolution.

A screen for deficiencies in GPI-anchorage of wall glycoproteins in yeast

Many of the genes and enzymes critical for assembly and biogenesis of yeast cell walls remain unidentified or poorly characterized. Therefore, we designed a high throughput genomic screen for defects in anchoring of GPI-cell wall proteins (GPI-CWPs), based on quantification of a secreted GFP-Sag1p fusion protein. Saccharomyces cerevisiae diploid deletion strains were transformed with a plasmid expressing the fusion protein under a GPD promoter, then GFP fluorescence was determined in culture supernatants after mid-exponential growth. Variability in the amount of fluorescent marker secreted into the medium was reduced by growth at 18 degrees C in buffered defined medium in the presence of sorbitol. Secondary screens included immunoblotting for GFP, fluorescence emission spectra, cell surface fluorescence, and cell integrity. Of 167 mutants deleted for genes affecting cell wall biogenesis or structure, eight showed consistent hyper-secretion of GFP relative to parental strain BY4743: tdh3 (glyceraldehyde-3-phosphate dehydrogenase), gda1 (guanosine diphosphatase), gpi13 and mcd4 (both ethanolamine phosphate-GPI-transferases), kre5 and kre1 (involved in synthesis of beta1,6 glucan), dcw1(implicated in GPI-CWP cross-linking to cell wall glucan), and cwp1 (a major cell wall protein). In addition, deletion of a number of genes caused decreased secretion of GFP. These results elucidate specific roles for specific genes in cell wall biogenesis, including differentiating among paralogous genes.

α-1,6-Mannosylation of N-linked oligosaccharide present on cell wall proteins is required for their incorporation into the cell wall in the filamentous fungus Neurospora crassa

The enzyme α-1,6-mannosyltransferase (OCH-1) is required for the synthesis of galactomannans attached to the N-linked oligosaccharides of Neurospora crassa cell wall proteins. The Neurospora crassa och-1 mutant has a tight colonial phenotype and a defective cell wall. A carbohydrate analysis of the och-1 mutant cell wall revealed a 10-fold reduction in the levels of mannose and galactose and a total lack of 1,6-linked mannose residues. Analysis of the integral cell wall protein from wild-type and och-1 mutant cells showed that the mutant cell wall had reduced protein content. The och-1 mutant was found to secrete 18-fold more protein than wild-type cells. Proteomic analysis of the proteins released by the mutant into the growth medium identified seven of the major cell wall proteins. Western blot analysis of ACW-1 and GEL-1 (two glycosylphosphatidylinositol [GPI]-anchored proteins that are covalently integrated into the wild-type cell wall) showed that high levels of these proteins were being released into the medium by the och-1 mutant. High levels of ACW-1 and GEL-1 were also released from the och-1 mutant cell wall by subjecting the wall to boiling in a 1% SDS solution, indicating that these proteins are not being covalently integrated into the mutant cell wall. From these results, we conclude that N-linked mannosylation of cell wall proteins by OCH-1 is required for their efficient covalent incorporation into the cell wall.

Salivary histatin 5 internalization by translocation, but not endocytosis, is required for fungicidal activity in Candida albicans

Salivary histatin 5 (Hst 5) is a cationic salivary protein with high fungicidal activity against Candida albicans. Binding to the cell wall followed by intracellular translocation is required for killing; however, specific binding components and critical toxic events are not understood. In this study, laminarin (β-1,3-glucan) but not sialic acid, mannan or pustulan mediated Hst 5 binding to C. albicans, and was disassociated by 100 mM NaCl. Time-lapse confocal microscopy revealed a dose-dependent rate of cytosolic uptake of Hst 5 that invariably preceded propidium iodide (PI) entry, demonstrating that translocation itself does not disrupt membrane integrity. Cell toxicity was manifest by vacuolar expansion followed by PI entrance; however, loss of endocytotic vacuolar trafficking of Hst 5 did not reduce killing. Extracellular NaCl (100 mM), but not sorbitol, prevented vacuolar expansion and PI entry in cells already containing cytosolic Hst 5, thus showing a critical role for ionic balance in Hst 5 toxicity. Hst 5 uptake, but not cell wall binding, was blocked by pretreatment with azide or carbonyl cyanide m-chlorophenylhydrazone; however, 10% of de-energized cells had membrane disruption. Thus, Hst 5 is capable of heterogeneous intracellular entry routes, but only direct cytosolic translocation causes cell death as a result of ionic efflux.

Secretion is required for late events in the cell-fusion pathway of mating yeast

Secretory vesicles accumulate adjacent to the contact site between the two cells of a yeast mating pair before they fuse, but there is no direct evidence that secretion is required to complete fusion. In this study, temperature-sensitive secretion (sec(ts)) mutants were used to investigate the role of secretion in yeast cell fusion. Cell fusion arrested less than 5 minutes after inhibiting secretion. This rapid fusion arrest was not an indirect consequence of reduced mating pheromone signaling, mating-pair assembly or actin polarity. Furthermore, secretion was required to complete cell fusion when it was transiently inhibited by addition and removal of the lipophilic styryl dye, FM4-64. These results indicate that ongoing secretion is required for late events in the cell-fusion pathway, which include plasma-membrane fusion and the completion of cell-wall remodeling, and they demonstrate a just-in-time delivery mechanism for the cell-fusion machinery.

Analysis of flocculins in Ashbya gossypii reveals FIG2 regulation by TEC1

For 95% of the Ashbya gossypii protein-encoding genes there is a Saccharomyces cerevisiae homolog. Out of these 90% are arranged in a conserved, syntenic, gene order. Interestingly, A. gossypii adhesins, encoded by homologs of S. cerevisiae FLO-genes, are found in non-syntenic positions. A. gossypii contains only a small set of adhesins: two FLO5, a FLO11 and a FIG2 homolog, but no FLO1, FLO9, or FLO10 homolog. Here we present the functional analysis of the A. gossypii adhesins and their potential transcriptional regulators SFL1, FLO8, and TEC1. Deletion of individual classes of FLO-genes did not reveal any phenotype. Lack of SFL1 or FLO8 showed reduced growth. The expression of adhesins in different strain backgrounds was tested using promoter-lacZ-fusions. We found that SFL1 acts as a suppressor of one of the FLO5 genes and FLO8 but particularly of FIG2. Interestingly, FIG2 expression was abolished in a tec1 mutant. We identified three potential Tec1-binding sites in the FIG2-promoter by similarity to S. cerevisiae Tec1-binding sites. The AgCHT2 promoter, which regulates a sporulation specific chitinase, also harbours potential Tec1-binding sites. Consequently, expression of CHT2 was not detected in a tec1 strain. This suggests that Tec1- binding sites are conserved between A. gossypii and S. cerevisiae even though there are different Tec1 target genes in each of these organisms.