TY - THES A1 - Mottola, Austin T1 - Molecular characterization of the SNF1 signaling pathway in \(Candida\) \(albicans\) T1 - Molekulare Charakterisierung des SNF1-Signalweges von \(Candida\) \(albicans\) N2 - The fungus Candida albicans is a typical member of the human microbiota, where it usually behaves as a commensal. It can also become pathogenic; often causing minor superficial infections in healthy people, but also potentially fatal invasive systemic infections in immunocompromised people. Unfortunately, there is only a fairly limited set of antifungal drugs, and evolution of drug resistance threatens their efficacy. Greater understanding of the mechanisms that C. albicans uses to survive in and infect the host can uncover candidate targets for novel antifungals. Protein kinases are central to a vast array of signalling pathways which govern practically all aspects of life, and furthermore are relatively straightforward to design drugs against. As such, investigation and characterization of protein kinases in C. albicans as well as their target proteins and the pathways they govern are important targets for research. AMP-activated kinases are well conserved proteins which respond to energy stress; they are represented in yeasts by the heterotrimeric SNF1 complex, which responds primarily to the absence of glucose. In this work, the SNF1 pathway was investigated with two primary goals: identify novel targets of this protein kinase and elucidate why SNF1 is essential. Two approaches were used to identify novel targets of SNF1. In one, suppressor mutants were evolved from a strain in which SNF1 activity is reduced, which exhibits defects in carbon source utilization and cell wall integrity. This revealed a suppressor mutation within SNF1 itself, coding for the catalytic subunit of the complex – SNF1Δ311-316. The second approach screened a library of artificially activated zinc cluster transcription factors, identifying Czf1 as one such transcription factor which, upon artificial activation, restored resistance to cell wall stress in a mutant of the SNF1 pathway. Finally, a, inducible gene deletion system revealed that SNF1 is not an essential gene. N2 - Der Pilz Candida albicans ist ein typisches Mitglied der menschlichen Mikrobiota, wo er sich normalerweise als Kommensale verhält. Als fakultativ pathogener Erreger kann er jedoch auch leichte, überfachliche Infektionen bei gesunden Menschen verursachen, sowie potenziell tödliche, invasive systemische Infektionen bei immungeschwächten Menschen. Leider gibt es nur eine recht begrenzte Anzahl von Antimykotika, und die Entwicklung von Resistenzen bedroht deren Wirksamkeit. Ein besseres Verständnis der Mechanismen, die C. albicans nutzt, um im Wirt zu überleben und ihn zu infizieren, kann mögliche Angriffspunkte für neue Antimykotika aufdecken. Proteinkinasen sind von zentraler Bedeutung für eine Vielzahl von Signalwegen, die praktisch alle Aspekte des Lebens steuern und gegen die sich zudem relativ einfach Medikamente entwickeln lassen. Daher ist die Untersuchung und Charakterisierung von Proteinkinasen in C. albicans sowie ihrer Zielproteine und der von ihnen gesteuerten Signalwege ein wichtiges Ziel für die Forschung. AMP-aktivierte Kinasen sind hoch konservierte Proteine, die auf Energiestress reagieren; sie sind in Hefen durch den heterotrimeren SNF1-Komplex vertreten, der vor allem auf das Fehlen von Glukose reagiert. In dieser Arbeit wurde der SNF1-Signalweg mit zwei primären Zielen untersucht: die Identifizierung neuer Zielproteine dieser Proteinkinase und die Klärung der Frage, warum SNF1 essentiell ist. Für die Identifikation neuer Zielproteine von SNF1 wurden zwei Ansätze verwendet. Zum einen wurde ein Stamm mit reduzierter SNF1-Aktivität, für die Entwicklung von Suppressor-Mutanten verwendet, die einen Defekte bei der Verwertung von Kohlenstoffquellen und eine eingeschränkte Zellwandintegrität aufweisen. Dabei wurde eine Suppressormutation in SNF1 selbst entdeckt, die für die katalytische Untereinheit des Komplexes – SNF1Δ311-316 - kodiert. Für den zweite Ansatz wurde eine Bibliothek von künstlich aktivierten Zink-Cluster-Transkriptionsfaktoren untersucht. Dies führte zur Identifikation von Czf1 als einen solchen Transkriptionsfaktor, der nach künstlicher Aktivierung die Resistenz gegen Zellwandstress in einer Mutante des SNF1- Signalweges wiederherstellte. Schließlich zeigte ein induzierbares Gendeletionssystem, dass SNF1 kein essentielles Gen ist. KW - candida albicans KW - yeast KW - fungus KW - candida KW - kinase KW - cell wall Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-238098 ER - TY - JOUR A1 - Mottola, Austin A1 - Ramírez-Zavala, Bernardo A1 - Hünninger, Kerstin A1 - Kurzai, Oliver A1 - Morschhäuser, Joachim T1 - The zinc cluster transcription factor Czf1 regulates cell wall architecture and integrity in Candida albicans JF - Molecular Microbiology N2 - The fungal cell wall is essential for the maintenance of cellular integrity and mediates interactions of the cells with the environment. It is a highly flexible organelle whose composition and organization is modulated in response to changing growth conditions. In the pathogenic yeast Candida albicans, a network of signaling pathways regulates the structure of the cell wall, and mutants with defects in these pathways are hypersensitive to cell wall stress. By harnessing a library of genetically activated forms of all C. albicans zinc cluster transcription factors, we found that a hyperactive Czf1 rescued the hypersensitivity to cell wall stress of different protein kinase deletion mutants. The hyperactive Czf1 induced the expression of many genes with cell wall-related functions and caused visible changes in the cell wall structure. C. albicans czf1Δ mutants were hypersensitive to the antifungal drug caspofungin, which inhibits cell wall biosynthesis. The changes in cell wall architecture caused by hyperactivity or absence of Czf1 resulted in an increased recognition of C. albicans by human neutrophils. Our results show that Czf1, which is known as a regulator of filamentous growth and white-opaque switching, controls the expression of cell wall genes and modulates the architecture of the cell wall. KW - cell wall KW - zinc cluster transcription factor KW - Candida albicans KW - protein kinases Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-259583 VL - 116 IS - 2 ER - TY - JOUR A1 - Mottola, Austin A1 - Schwanfelder, Sonja A1 - Morschhäuser, Joachim T1 - Generation of Viable Candida albicans Mutants Lacking the "Essential" Protein Kinase Snf1 by Inducible Gene Deletion JF - mSphere N2 - The protein kinase Snf1, a member of the highly conserved AMP-activated protein kinase family, is a central regulator of metabolic adaptation. In the pathogenic yeast Candida albicans, Snf1 is considered to be essential, as previous attempts by different research groups to generate homozygous snf1 Delta mutants were unsuccessful. We aimed to elucidate why Snf1 is required for viability in C. albicans by generating snf1 Delta null mutants through forced, inducible gene deletion and observing the terminal phenotype before cell death. Unexpectedly, we found that snf1 Delta mutants were viable and could grow, albeit very slowly, on rich media containing the preferred carbon source glucose. Growth was improved when the cells were incubated at 37 degrees C instead of 30 degrees C, and this phenotype enabled us to isolate homozygous snf1 Delta mutants also by conventional, sequential deletion of both SNF1 alleles in a wild-type C. albicans strain. All snf1 Delta mutants could grow slowly on glucose but were unable to utilize alternative carbon sources. Our results show that, under optimal conditions, C. albicans can live and grow without Snf1. Furthermore, they demonstrate that inducible gene deletion is a powerful method for assessing gene essentiality in C. albicans. IMPORTANCE Essential genes are those that are indispensable for the viability and growth of an organism. Previous studies indicated that the protein kinase Snf1, a central regulator of metabolic adaptation, is essential in the pathogenic yeast Candida albicans, because no homozygous snf1 deletion mutants of C. albicans wild-type strains could be obtained by standard approaches. In order to investigate the lethal consequences of SNF1 deletion, we generated conditional mutants in which SNF1 could be deleted by forced, inducible excision from the genome. Unexpectedly, we found that snf1 null mutants were viable and could grow slowly under optimal conditions. The growth phenotypes of the snf1 Delta mutants explain why such mutants were not recovered in previous attempts. Our study demonstrates that inducible gene deletion is a powerful method for assessing gene essentiality in C. albicans. KW - Candida albicans KW - Snf1 KW - conditional mutants KW - essential genes KW - protein kinases Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230524 VL - 5 IS - 4 ER - TY - JOUR A1 - Mottola, Austin A1 - Morschhäuser, Joachim T1 - An intragenic recombination event generates a Snf4-independent form of the essential protein kinase SNF1 in Candida albicans JF - mSphere N2 - The heterotrimeric protein kinase SNF1 plays a key role in the metabolic adaptation of the pathogenic yeast Candida albicans. It consists of the essential catalytic α-subunit Snf1, the γ-subunit Snf4, and one of the two β-subunits Kis1 and Kis2. Snf4 is required to release the N-terminal catalytic domain of Snf1 from autoinhibition by the C-terminal regulatory domain, and snf4Δ mutants cannot grow on carbon sources other than glucose. In a screen for suppressor mutations that restore growth of a snf4Δ mutant on alternative carbon sources, we isolated a mutant in which six amino acids between the N-terminal kinase domain and the C-terminal regulatory domain of Snf1 were deleted. The deletion was caused by an intragenic recombination event between two 8-bp direct repeats flanking six intervening codons. In contrast to truncated forms of Snf1 that contain only the kinase domain, the Snf4-independent Snf1\(^{Δ311 − 316}\) was fully functional and could replace wild-type Snf1 for normal growth, because it retained the ability to interact with the Kis1 and Kis2 β-subunits via its C-terminal domain. Indeed, the Snf4-independent Snf1\(^{Δ311 − 316}\) still required the β-subunits of the SNF1 complex to perform its functions and did not rescue the growth defects of kis1Δ mutants. Our results demonstrate that a preprogrammed in-frame deletion event within the SNF1 coding region can generate a mutated form of this essential kinase which abolishes autoinhibition and thereby overcomes growth deficiencies caused by a defect in the γ-subunit Snf4. KW - AMP-activated kinases KW - Candida albicans KW - genetic recombination KW - metabolic adaptation KW - suppressor mutation Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-202170 VL - 4 IS - 3 ER - TY - JOUR A1 - Ramírez-Zavala, Bernardo A1 - Betsova, Darina A1 - Schwanfelder, Sonja A1 - Krüger, Ines A1 - Mottola, Austin A1 - Krüger, Thomas A1 - Kniemeyer, Olaf A1 - Brakhage, Axel A. A1 - Morschhäuser, Joachim T1 - Multiple phosphorylation sites regulate the activity of the repressor Mig1 in \(Candida\) \(albicans\) JF - mSphere N2 - ABSTRACT The highly conserved heterotrimeric protein kinase SNF1 is important for metabolic adaptations in the pathogenic yeast Candida albicans. A key function of SNF1 is to inactivate the repressor protein Mig1 and thereby allow the expression of genes that are required for the utilization of alternative carbon sources when the preferred carbon source, glucose, is absent or becomes limiting. However, how SNF1 controls Mig1 activity in C. albicans has remained elusive. Using a phosphoproteomics approach, we found that Mig1 is phosphorylated at multiple serine residues. Replacement of these serine residues by nonphosphorylatable alanine residues strongly increased the repressor activity of Mig1 in cells lacking a functional SNF1 complex, indicating that additional protein kinases are involved in the regulation of Mig1. Unlike wild-type Mig1, whose levels strongly decreased when the cells were grown on sucrose or glycerol instead of glucose, the levels of a mutant Mig1 protein lacking nine phosphorylation sites remained high under these conditions. Despite the increased protein levels and the absence of multiple phosphorylation sites, cells with a functional SNF1 complex could still sufficiently inhibit the hyperactive Mig1 to enable wild-type growth on alternative carbon sources. In line with this, phosphorylated forms of the mutant Mig1 were still detected in the presence and absence of a functional SNF1, demonstrating that Mig1 contains additional, unidentified phosphorylation sites and that downstream protein kinases are involved in the control of Mig1 activity by SNF1. IMPORTANCE The SNF1 protein kinase signaling pathway, which is highly conserved in eukaryotic cells, is important for metabolic adaptations in the pathogenic yeast Candida albicans. However, so far, it has remained elusive how SNF1 controls the activity of one of its main effectors, the repressor protein Mig1 that inhibits the expression of genes required for the utilization of alternative carbon sources when glucose is available. In this study, we have identified multiple phosphorylation sites in Mig1 that contribute to its inactivation. Mutation of these sites strongly increased Mig1 repressor activity in the absence of SNF1, but SNF1 could still sufficiently inhibit the hyperactive Mig1 to enable growth on alternative carbon sources. These findings reveal features of Mig1 that are important for controlling its repressor activity. Furthermore, they demonstrate that both SNF1 and additional protein kinases regulate Mig1 in this pathogenic yeast. KW - Candida albicans KW - SNF1 KW - Mig1 KW - protein kinase KW - signaling pathway Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-350060 VL - 8 IS - 6 ER -