scholarly journals Distinct transport mechanism in Candida albicans methylammonium permeases

2020 ◽  
Vol 19 (10) ◽  
pp. 1143-1149
Author(s):  
B. Neuhäuser
Keyword(s):  
Candida Albicans ◽  
Xenopus Laevis ◽  
Growth And Development ◽  
Transport Mechanism ◽  
Filamentous Growth ◽  
Ammonium Transport ◽  
Pseudohyphal Growth ◽  
Ph Dependent ◽  
External Ph

Abstract It is crucial for the growth and development of an organism whether ammonium is transported across its membranes in a form of NH4+ or NH3. The transport of both molecules follows different pH-dependent gradients across membranes and transport of both substrates differentially affects the internal and external pH. As a consequence, they directly influence the physiology and organism development. CaMep2 from Candida albicans shows a dual transceptor function in ammonium transport and sensing. CaMep2 senses low ammonium availability and induces filamentous growth. CaMep1, by contrast, is only active in transport, but not involved in ammonium signaling. Here, both proteins were heterologously expressed in Xenopus laevis oocytes. This study identified electrogenic NH4+ transport by CaMep1 and electroneutral NH3 transport by CaMep2, which might be a prerequisite for the induction of pseudohyphal growth.

scholarly journals Mutational Analysis of the Candida albicans Ammonium Permease Mep2p Reveals Residues Required for Ammonium Transport and Signaling

2008 ◽  
Vol 8 (2) ◽  
pp. 147-160 ◽  
Author(s):  
Neelam Dabas ◽  
Sabrina Schneider ◽  
Joachim Morschhäuser
Keyword(s):  
Candida Albicans ◽  
Amino Acid ◽  
Filamentous Growth ◽  
Ammonium Uptake ◽  
Ammonium Ion ◽  
Ammonium Transport ◽  
Filament Formation ◽  
Pathogenic Yeast ◽  
Signaling Domain ◽  
Signaling Activity

ABSTRACT The ammonium permease Mep2p mediates ammonium uptake and also induces filamentous growth in the human-pathogenic yeast Candida albicans in response to nitrogen limitation. The C-terminal cytoplasmic tail of Mep2p contains a signaling domain that is not required for ammonium transport but is essential for Mep2p-dependent morphogenesis. Progressive C-terminal truncations showed Y433 to be the last amino acid that is essential for the induction of filamentous growth, thereby delimiting the Mep2p signaling domain. To understand in more detail how the signaling activity of Mep2p is regulated by ammonium availability and transport, we mutated conserved amino acid residues that have been implicated in ammonium binding or uptake. Mutation of D180, which has been proposed to mediate initial contact with extracellular ammonium, or the pore-lining residues H188 and H342 abolished Mep2p expression, indicating that these residues are important for protein stability. Mutation of F239, which together with F126 is thought to form an extracytosolic gate to the conductance channel, abolished both ammonium uptake and Mep2p-dependent filament formation, despite proper localization of the protein. On the other hand, mutation of W167, which is assumed to participate with Y122, F126, and S243 in the recruitment and coordination of the ammonium ion at the extracytosolic side of the cell membrane, also abolished filament formation without having a strong impact on ammonium transport, demonstrating that extracellular alterations in Mep2p can affect intracellular signaling. Mutation of Y122 reduced ammonium uptake much more strongly than mutation of W167 but still allowed efficient filament formation, indicating that the signaling activity of Mep2p is not directly correlated with its transport activity. These results provide important insights into ammonium transport and control of morphogenesis by Mep2p in C. albicans.

scholarly journals Role of the Npr1 Kinase in Ammonium Transport and Signaling by the Ammonium Permease Mep2 in Candida albicans

2011 ◽  
Vol 10 (3) ◽  
pp. 332-342 ◽  
Author(s):  
Benjamin Neuhäuser ◽  
Nico Dunkel ◽  
Somisetty V. Satheesh ◽  
Joachim Morschhäuser
Keyword(s):  
Candida Albicans ◽  
Filamentous Growth ◽  
Ammonium Uptake ◽  
Ammonium Transport ◽  
Content Type ◽  
Low Concentrations ◽  
In The Wild ◽  
Signaling Activity ◽  
Nitrogen Conditions

ABSTRACT The ammonium permease Mep2 induces a switch from unicellular yeast to filamentous growth in response to nitrogen limitation in Saccharomyces cerevisiae and Candida albicans . In S. cerevisiae , the function of Mep2 and other ammonium permeases depends on the protein kinase Npr1. Mutants lacking NPR1 cannot grow on low concentrations of ammonium and do not filament under limiting nitrogen conditions. A G349C mutation in Mep2 renders the protein independent of Npr1 and results in increased ammonium transport and hyperfilamentous growth, suggesting that the signaling activity of Mep2 directly correlates with its ammonium transport activity. In this study, we investigated the role of Npr1 in ammonium transport and Mep2-mediated filamentation in C. albicans . We found that the two ammonium permeases Mep1 and Mep2 of C. albicans differ in their dependency on Npr1. While Mep1 could function well in the absence of the Npr1 kinase, ammonium transport by Mep2 was virtually abolished in npr1 Δ mutants. However, the dependence of Mep2 activity on Npr1 was relieved at higher temperatures (37°C), and Mep2 could efficiently induce filamentous growth under limiting nitrogen conditions in npr1 Δ mutants. Like in S. cerevisiae , mutation of the conserved glycine at position 343 in Mep2 of C. albicans to cysteine resulted in Npr1-independent ammonium uptake. In striking contrast, however, the mutation abolished the ability of Mep2 to induce filamentous growth both in the wild type and in npr1 Δ mutants. Therefore, a mutation that improves ammonium transport by Mep2 under nonpermissible conditions eliminates its signaling activity in C. albicans .

scholarly journals Global Role of Cyclic AMP Signaling in pH-Dependent Responses in Candida albicans

mSphere ◽  
2016 ◽  
Vol 1 (6) ◽  
Author(s):  
Jeffrey M. Hollomon ◽  
Nora Grahl ◽  
Sven D. Willger ◽  
Katja Koeppen ◽  
Deborah A. Hogan
Keyword(s):  
Candida Albicans ◽  
Cyclic Amp ◽  
Hyphal Growth ◽  
Filamentous Growth ◽  
Low Ph ◽  
Camp Signaling ◽  
Content Type ◽  
Neutral Ph ◽  
Ph Dependent

ABSTRACT Candida albicans is a human commensal and the causative agent of candidiasis, a potentially invasive and life-threatening infection. C. albicans experiences wide changes in pH during both benign commensalism (a common condition) and pathogenesis, and its morphology changes in response to this stimulus. Neutral pH is considered an activator of hyphal growth through Rim101, but the effect of low pH on other morphology-related pathways has not been extensively studied. We sought to determine the role of cyclic AMP signaling, a central regulator of morphology, in the sensing of pH. In addition, we asked broadly what cellular processes were altered by pH in both the presence and absence of this important signal integration system. We concluded that cAMP signaling is impacted by pH and that cAMP broadly impacts C. albicans physiology in both pH-dependent and -independent ways. Candida albicans behaviors are affected by pH, an important environmental variable. Filamentous growth is a pH-responsive behavior, where alkaline conditions favor hyphal growth and acid conditions favor growth as yeast. We employed filamentous growth as a tool to study the impact of pH on the hyphal growth regulator Cyr1, and we report that downregulation of cyclic AMP (cAMP) signaling by acidic pH contributes to the inhibition of hyphal growth in minimal medium with GlcNAc. Ras1 and Cyr1 are generally required for efficient hyphal growth, and the effects of low pH on Ras1 proteolysis and GTP binding are consistent with diminished cAMP output. Active alleles of ras1 do not suppress the hyphal growth defect at low pH, while dibutyryl cAMP partially rescues filamentous growth at low pH in a cyr1 mutant. These observations are consistent with Ras1-independent downregulation of Cyr1 by low pH. We also report that extracellular pH leads to rapid and prolonged decreases in intracellular pH, and these changes may contribute to reduced cAMP signaling by reducing intracellular bicarbonate pools. Transcriptomics analyses found that the loss of Cyr1 at either acidic or neutral pH leads to increases in transcripts involved in carbohydrate catabolism and protein translation and glycosylation and decreases in transcripts involved in oxidative metabolism, fluconazole transport, metal transport, and biofilm formation. Other pathways were modulated in pH-dependent ways. Our findings indicate that cAMP has a global role in pH-dependent responses, and this effect is mediated, at least in part, through Cyr1 in a Ras1-independent fashion. IMPORTANCE Candida albicans is a human commensal and the causative agent of candidiasis, a potentially invasive and life-threatening infection. C. albicans experiences wide changes in pH during both benign commensalism (a common condition) and pathogenesis, and its morphology changes in response to this stimulus. Neutral pH is considered an activator of hyphal growth through Rim101, but the effect of low pH on other morphology-related pathways has not been extensively studied. We sought to determine the role of cyclic AMP signaling, a central regulator of morphology, in the sensing of pH. In addition, we asked broadly what cellular processes were altered by pH in both the presence and absence of this important signal integration system. We concluded that cAMP signaling is impacted by pH and that cAMP broadly impacts C. albicans physiology in both pH-dependent and -independent ways.

scholarly journals TUP1, CPH1 and EFG1 Make Independent Contributions to Filamentation in Candida albicans

Genetics ◽  
2000 ◽  
Vol 155 (1) ◽  
pp. 57-67 ◽  
Author(s):  
Burkhard R Braun ◽  
Alexander D Johnson
Keyword(s):  
Candida Albicans ◽  
Environmental Conditions ◽  
Target Genes ◽  
Single Cells ◽  
Filamentous Growth ◽  
Surface Proteins ◽  
Pathway Expression ◽  
Separate Pathway ◽  
The Common ◽  
Growth Pathway

Abstract The common fungal pathogen, Candida albicans, can grow either as single cells or as filaments (hyphae), depending on environmental conditions. Several transcriptional regulators have been identified as having key roles in controlling filamentous growth, including the products of the TUP1, CPH1, and EFG1 genes. We show, through a set of single, double, and triple mutants, that these genes act in an additive fashion to control filamentous growth, suggesting that each gene represents a separate pathway of control. We also show that environmentally induced filamentous growth can occur even in the absence of all three of these genes, providing evidence for a fourth regulatory pathway. Expression of a collection of structural genes associated with filamentous growth, including HYR1, ECE1, HWP1, ALS1, and CHS2, was monitored in strains lacking each combination of TUP1, EFG1, and CPH1. Different patterns of expression were observed among these target genes, supporting the hypothesis that these three regulatory proteins engage in a network of individual connections to downstream genes and arguing against a model whereby the target genes are regulated through a central filamentous growth pathway. The results suggest the existence of several distinct types of filamentous forms of C. albicans, each dependent on a particular set of environmental conditions and each expressing a unique set of surface proteins.

scholarly journals Invasive Filamentous Growth ofCandida albicansIs Promoted by Czf1p-Dependent Relief of Efg1p-Mediated Repression

Genetics ◽  
2002 ◽  
Vol 160 (4) ◽  
pp. 1749-1753 ◽  
Author(s):  
Angela D Giusani ◽  
Marcelo Vinces ◽  
Carol A Kumamoto
Keyword(s):  
Candida Albicans ◽  
Filamentous Growth ◽  
Environmental Cues ◽  
Complex Regulation

AbstractFilamentation of Candida albicans occurs in response to many environmental cues. During growth within matrix, Efg1p represses filamentation and Czf1p relieves this repression. We propose that Czf1p interacts with Efg1p, altering its function. The complex regulation of filamentation may reflect the versatility of C. albicans as a pathogen.

scholarly journals Identification and Characterization of TUP1-Regulated Genes in Candida albicans

Genetics ◽  
2000 ◽  
Vol 156 (1) ◽  
pp. 31-44 ◽  
Author(s):  
Burkhard R Braun ◽  
W Steven Head ◽  
Ming X Wang ◽  
Alexander D Johnson
Keyword(s):  
Candida Albicans ◽  
Systemic Infection ◽  
Subtractive Hybridization ◽  
Filamentous Growth ◽  
Surface Proteins ◽  
Infection Model ◽  
Ferric Reductase ◽  
Pathogenesis Related Protein ◽  
Plant Pathogenesis ◽  
Rnase T2

Abstract TUP1 encodes a transcriptional repressor that negatively controls filamentous growth in Candida albicans. Using subtractive hybridization, we identified six genes, termed repressed by TUP1 (RBT), whose expression is regulated by TUP1. One of the genes (HWP1) has previously been characterized, and a seventh TUP1-repressed gene (WAP1) was recovered due to its high similarity to RBT5. These genes all encode secreted or cell surface proteins, and four out of the seven (HWP1, RBT1, RBT5, and WAP1) encode putatively GPI-modified cell wall proteins. The remaining three, RBT2, RBT4, and RBT7, encode, respectively, an apparent ferric reductase, a plant pathogenesis-related protein (PR-1), and a putative secreted RNase T2. The expression of RBT1, RBT4, RBT5, HWP1, and WAP1 was induced in wild-type cells during the switch from the yeast form to filamentous growth, indicating the importance of TUP1 in regulating this process and implicating the RBTs in hyphal-specific functions. We produced knockout strains in C. albicans for RBT1, RBT2, RBT4, RBT5, and WAP1 and detected no phenotypes on several laboratory media. However, two animal models for C. albicans infection, a rabbit cornea model and a mouse systemic infection model, revealed that rbt1Δ and rbt4Δ strains had significantly reduced virulence. TUP1 appears, therefore, to regulate many genes in C. albicans, a significant fraction of which are induced during filamentous growth, and some of which participate in pathogenesis.

scholarly journals CAP1, an Adenylate Cyclase-Associated Protein Gene, Regulates Bud-Hypha Transitions, Filamentous Growth, and Cyclic AMP Levels and Is Required for Virulence of Candida albicans

2001 ◽  
Vol 183 (10) ◽  
pp. 3211-3223 ◽  
Author(s):  
Yong-Sun Bahn ◽  
Paula Sundstrom
Keyword(s):  
Candida Albicans ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Germ Tube ◽  
Filamentous Growth ◽  
Tube Formation ◽  
Camp Signaling ◽  
Solid Media ◽  
Opportunistic Fungal Pathogen ◽  
Camp Levels

ABSTRACT In response to a wide variety of environmental stimuli, the opportunistic fungal pathogen Candida albicans exits the budding cycle, producing germ tubes and hyphae concomitant with expression of virulence genes, such as that encoding hyphal wall protein 1 (HWP1). Biochemical studies implicate cyclic AMP (cAMP) increases in promoting bud-hypha transitions, but genetic evidence relating genes that control cAMP levels to bud-hypha transitions has not been reported. Adenylate cyclase-associated proteins (CAPs) of nonpathogenic fungi interact with Ras and adenylate cyclase to increase cAMP levels under specific environmental conditions. To initiate studies on the relationship between cAMP signaling and bud-hypha transitions in C. albicans, we identified, cloned, characterized, and disrupted the C. albicans CAP1 gene. C. albicans strains with inactivated CAP1 budded in conditions that led to germ tube formation in isogenic strains withCAP1. The addition of 10 mM cAMP and dibutyryl cAMP promoted bud-hypha transitions and filamentous growth in thecap1/cap1 mutant in liquid and solid media, respectively, showing clearly that cAMP promotes hypha formation in C. albicans. Increases in cytoplasmic cAMP preceding germ tube emergence in strains having CAP1 were markedly diminished in the budding cap1/cap1 mutant. C. albicans strains with deletions of both alleles ofCAP1 were avirulent in a mouse model of systemic candidiasis. The avirulence of a germ tube-deficientcap1/cap1 mutant coupled with the role of Cap1 in regulating cAMP levels shows that the Cap1-mediated cAMP signaling pathway is required for bud-hypha transitions, filamentous growth, and the pathogenesis of candidiasis.

scholarly journals Mitochondrial perturbation reduces susceptibility to xenobiotics through altered efflux in Candida albicans

Genetics ◽  
2021 ◽  
Author(s):  
Saif Hossain ◽  
Amanda O Veri ◽  
Zhongle Liu ◽  
Kali R Iyer ◽  
Teresa R O’Meara ◽  
...  
Keyword(s):  
Candida Albicans ◽  
Mitochondrial Function ◽  
Efflux Pump ◽  
Systemic Disease ◽  
Filamentous Growth ◽  
Hsp90 Inhibitor ◽  
Homozygous Deletion ◽  
Hsp90 Inhibitors ◽  
Hsp90 Inhibition ◽  
Conditional Expression

Abstract Candida albicans is a leading human fungal pathogen, which can cause superficial infections or life-threatening systemic disease in immunocompromised individuals. The ability to transition between yeast and filamentous forms is a major virulence trait of C. albicans, and a key regulator of this morphogenetic transition is the molecular chaperone Hsp90. To explore the mechanisms governing C. albicans morphogenesis in response to Hsp90 inhibition, we performed a functional genomic screen using the gene replacement and conditional expression (GRACE) collection to identify mutants that are defective in filamentation in response to the Hsp90 inhibitor, geldanamycin. We found that transcriptional repression of genes involved in mitochondrial function blocked filamentous growth in response to the concentration of Hsp90 inhibitor used in the screen, and this was attributable to increased resistance to the compound. Further exploration revealed that perturbation of mitochondrial function reduced susceptibility to two structurally distinct Hsp90 inhibitors, geldanamycin and radicicol, such that filamentous growth was restored in the mitochondrial mutants by increasing the compound concentration. Deletion of two representative mitochondrial genes, MSU1 and SHY1, enhanced cellular efflux and reduced susceptibility to diverse intracellularly acting compounds. Additionally, screening a C. albicans efflux pump gene deletion library implicated Yor1 in efflux of geldanamycin and Cdr1, in efflux of radicicol. Deletion of these transporter genes restored sensitivity to Hsp90 inhibitors in MSU1 and SHY1 homozygous deletion mutants, thereby enabling filamentation. Taken together, our findings suggest that mitochondrial dysregulation elevates cellular efflux and consequently reduces susceptibility to xenobiotics in C. albicans.

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