Advances in targeting the vacuolar proton-translocating ATPase (V-ATPase) for anti-fungal therapy

A key amino acid substitution of vacuolar-type H+-ATPases A subunit (VATP-A) confers selective toxicity of a potential botanical insecticide, periplocoside P (PSP), in Mythimna separata and Spodoptera exigua

Periplocosides, extracted from the root bark of Periploca sepium, are plant secondary compounds known to inhibit the V-ATPase enzyme in susceptible insect species, such as Mythimna separata. However, many species, including Spodoptera exigua, show resistance to these compounds. Previous studies identified the V-ATPase subunit A (VATP-A) in the midgut epithelium of M. separata as the putative target of periplocoside P (PSP), but the specific amino acids involved in this interaction remained unclear. In this study, we demonstrate the selective toxicity of PSP and its inhibition effect on V-ATPase. Molecular docking identified potential interactions between PSP and three amino acids (K85, R171, E199) in MsVATP-A, with in vitro binding assays revealing that K85 and R171 serve as the primary binding sites. Notably, sequence alignment revealed that R171 in sensitive species is substituted with K in resistant species. To investigate the functional implications of this substitution, we performed in vitro site-directed mutagenesis to exchange the corresponding amino acids between the VATP-A orthologs of M. separata and S. exigua. The R171K mutation in MsVATP-A reduced binding to PSP, while the K170R mutation in SeVATP-A enhanced it. Furthermore, in vivo genome editing in Drosophila melanogaster, a PSP-sensitive species, revealed that the R168K mutation conferred 15.78-fold resistance to PSP compared to the wild-type strain (w1118). Our findings confirm the role of VATP-A as the target of PSP and elucidate the key amino acids influencing its insecticidal selectivity. This research enhances the understanding of the molecular interactions between natural compounds and insect targets, offering insights for the development of targeted pest control strategies.

Discovery of the Chlorinated and Ammoniated Derivatives of Vanillin as Potential Insecticidal Candidates Targeting V-ATPase: Structure-Based Virtual Screening, Synthesis, and Bioassay

Vacuolar-type H+-ATPases (V-ATPases) play a crucial role in the life cycle of agricultural pests and represent a promising target for the development of novel insecticides. In this study, S18, a derivative of vanillin acquired from Specs database using a structure-based virtual screening methodology, was first identified as a V-ATPase inhibitor. It binds to subunit A of the enzyme with a Kd of 1 nM and exhibits insecticidal activity against M. separata. Subsequently, using S18 as the lead compound, a new series of vanillin derivatives were rationally designed and efficiently synthesized. and their biological activities were assessed. Among them, compound 3b-03 showed the strongest insecticidal activity against M. separata by effectively targeting the V-ATPase subunit A with Kd of 0.803 μM. Isothermal titration calorimetric measurements and docking results provided insights into its interaction with subunit A of V-ATPase, which could facilitate future research aimed at the development of novel chemical insecticides.

Ultrastructural and morphological studies on variables affecting Escherichia coli with selected commercial antibiotics

Background

Many studies reported the effects of antibiotic exposure on E. coli bacterial growth and cell modification. However, scarce descriptive information on ultrastructural effects upon exposure of commercial antibiotics.

Methods

This study described the morphological and ultrastructural alterations caused by selected antibiotics (amoxicillin-clavulanate, ceftriaxone, polymyxin B, colistin, gentamicin, and amikacin) that targeted cell wall, plasma membrane, and cytoplasmic density, and also proteins synthesis. We determined extracellular morphological changes of exposure through scanning electron microscopy (FESEM) and intracellular activities through transmission electron microscopy (TEM) investigation.

Results

FESEM and TEM micrograph of E. coli exposed with selected antibiotics shows ultrastructural changes in beta-lactam class (amoxicillin-clavulanate, ceftriaxone) elongated the cells as the cell wall was altered as it inhibits bacterial cell wall synthesis, polymyxin class (polymyxin B, colistin) had plasmid and curli-fimbriae as it breaking down the plasma/cytoplasmic membrane, and aminoglycoside class (gentamicin, and amikacin) reduced ribosome concentration as it inhibits bacterial protein synthesis by binding to 30 s ribosomes.

Conclusion

Morphological and ultrastructural alterations of E. coli's mechanism of actions were translated and depicted. This study could be reference for characterization studies for morphological and ultrastructural of E. coli upon exposure to antimicrobial agents.

Eukaryotic yeast V1-ATPase rotary mechanism insights revealed by high-resolution single-molecule studies

Vacuolar ATP-dependent proton pumps (V-ATPases) belong to a super-family of rotary ATPases and ATP synthases. The V1 complex consumes ATP to drive rotation of a central rotor that pumps protons across membranes via the Vo complex. Eukaryotic V-ATPases are regulated by reversible disassembly of subunit C, V1 without C, and VO. ATP hydrolysis is thought to generate an unknown rotary state that initiates regulated disassembly. Dissociated V1 is inhibited by subunit H that traps it in a specific rotational position. Here, we report the first single-molecule studies with high resolution of time and rotational position of Saccharomyces cerevisiae V1-ATPase lacking subunits H and C (V1ΔHC), which resolves previously elusive dwells and angular velocity changes. Rotation occurred in 120° power strokes separated by dwells comparable to catalytic dwells observed in other rotary ATPases. However, unique V1ΔHC rotational features included: 1) faltering power stroke rotation during the first 60°; 2) a dwell often occurring ∼45° after the catalytic dwell, which did not increase in duration at limiting MgATP; 3) a second dwell, ∼2-fold longer occurring 112° that increased in duration and occurrence at limiting MgATP; 4) limiting MgATP-dependent decreases in power stroke angular velocity where dwells were not observed. The results presented here are consistent with MgATP binding to the empty catalytic site at 112° and MgADP released at ∼45°, and provide important new insight concerning the molecular basis for the differences in rotary positions of substrate binding and product release between V-type and F-type ATPases.

In vitro interactions of proton pump inhibitors and azoles against pathogenic fungi

Introduction

Azole resistance has been increasingly reported and become an issue for clinical managements of invasive mycoses. New strategy with combination therapy arises as a valuable and promising alternative option. The aim of the present study is to investigate the in vitro combinational effect of proton pump inhibitors (PPIs) and azoles against pathogenic fungi.

Methods

In vitro interactions of PPIs including omeprazole (OME), lansoprazole (LAN), pantoprazole (PAN), and rabeprazole (RAB), and commonly used azoles including itraconazole (ITC), posaconazole (POS), voriconazole (VRC) and fluconazole (FLC), were investigated via broth microdilution chequerboard procedure adapted from the CLSI M27-A3 and M38-A2. A total of 67 clinically isolated strains, namely 27 strains of Aspergillus spp., 16 strains of Candida spp., and 24 strains of dematiaceous fungi, were studied. C. parapsilosis (ATCC 22019) and A. flavus (ATCC 204304) was included to ensure quality control.

Results

PPIs individually did not exert any significant antifungal activity. The combination of OME with ITC, POS, or VRC showed synergism against 77.6%, 86.6%, and 4% strains of tested pathogenic fungi, respectively, while synergism of OME/FLC was observed in 50% strains of Candida spp. Synergism between PAN and ITC, POS, or VRC was observed against 47.8%, 77.6% and 1.5% strains of tested fungi, respectively, while synergism of PNA/FLC was observed in 50% strains of Candida spp. Synergism of LAN with ITC, POS, or VRC was observed against 86.6%, 86.6%, and 3% of tested strains, respectively, while synergism of LAN/FLC was observed in 31.3% strains of Candida spp. Synergy of the combination of RAB with ITC, POS, or VRC was observed against 25.4%, 64.2%, and 4.5% of tested strains, respectively, while synergism of RAB/FLC was observed in 12.5% of Candida spp.. Among PPIs, synergism was least observed between RAB and triazoles, while among triazoles, synergism was least observed between VRC and PPIs. Among species, synergy was much more frequently observed in Aspergillus spp. and dematiaceous fungi as compared to Candida spp. Antagonism between PPIs with ITC or VRC was occasionally observed in Aspergillus spp. and dematiaceous fungi. It is notable that PPIs combined with azoles showed synergy against azole resistant A. fumigatus, and resulted in category change of susceptibility of ITC and POS against Candida spp.

Discussion

The results suggested that PPIs combined with azoles has the potential to enhance the susceptibilities of azoles against multiple pathogenic fungi and could be a promising strategy to overcome azole resistance issues. However, further investigations are warranted to study the combinational efficacy in more isolates and more species, to investigate the underlying mechanism of interaction and to evaluate the potential for concomitant use of these agents in human.

Carvacrol-Induced Vacuole Dysfunction and Morphological Consequences in Nakaseomyces glabratus and Candida albicans

With the prevalence of systemic fungal infections caused by Candida albicans and non-albicans species and their resistance to classical antifungals, there is an urgent need to explore alternatives. Herein, we evaluate the impact of the monoterpene carvacrol, a major component of oregano and thyme oils, on clinical and laboratory strains of C. albicans and Nakaseomyces glabratus. Carvacrol induces a wide range of antifungal effects, including the inhibition of growth and hyphal and biofilm formation. Using biochemical and microscopic approaches, we elucidate carvacrol-induced hyphal inhibition. The significantly reduced survival rates following exposure to carvacrol were accompanied by dose-dependent vacuolar acidification, disrupted membrane integrity, and aberrant morphology. Germ tube assays, used to elucidate the relationship between vacuolar dysfunction and hyphal inhibition, showed that carvacrol significantly reduced hyphal formation, which was accompanied by a defective C. albicans morphology. Thus, we show a link between vacuolar acidification/disrupted vacuole membrane integrity and compromised candidal morphology/morphogenesis, demonstrating that carvacrol exerts its anti-hyphal activity by altering vacuole integrity.

Location-biased activation of the proton-sensor GPR65 is uncoupled from receptor trafficking

The canonical view of G protein-coupled receptor (GPCR) function is that receptor trafficking is tightly coupled to signaling. GPCRs remain on the plasma membrane (PM) at the cell surface until they are activated, after which they are desensitized and internalized into endosomal compartments. This canonical view presents an interesting context for proton-sensing GPCRs because they are more likely to be activated in acidic endosomal compartments than at the PM. Here, we show that the trafficking of the prototypical proton-sensor GPR65 is fully uncoupled from signaling, unlike that of other known mammalian GPCRs. GPR65 internalizes and localizes to early and late endosomes, from where they signal at steady state, irrespective of extracellular pH. Acidic extracellular environments stimulate receptor signaling at the PM in a dose-dependent manner, although endosomal GPR65 is still required for a full signaling response. Receptor mutants that were incapable of activating cAMP trafficked normally, internalize and localize to endosomal compartments. Our results show that GPR65 is constitutively active in endosomes, and suggest a model where changes in extracellular pH reprograms the spatial pattern of receptor signaling and biases the location of signaling to the cell surface.

Significance of the plasma membrane H+-ATPase and V-ATPase for growth and pathogenicity in pathogenic fungi

Pathogenic fungi are widespread and cause a variety of diseases in human beings and other organisms. At present, limited classes of antifungal agents are available to treat invasive fungal diseases. With the wide use of the commercial antifungal agents, drug resistance of pathogenic fungi are continuously increasing. Therefore, exploring effective antifungal agents with novel drug targets is urgently needed to cope with the challenges that the antifungal area faces. pH homeostasis is vital for multiple cellular processes, revealing the potential for defining novel drug targets. Fungi have evolved a number of strategies to maintain a stable pH internal environment in response to rapid metabolism and a dramatically changing extracellular environment. Among them, plasma membrane H+-ATPase (PMA) and vacuolar H+-ATPase (V-ATPase) play a central role in the regulation of pH homeostasis system. In this chapter, we will summarize the current knowledge about pH homeostasis and its regulation mechanisms in pathogenic fungi, especially for the recent advances in PMA and V-ATPase, which would help in revealing the regulating mechanism of pH on cell growth and pathogenicity, and further designing effective drugs and identify new targets for combating fungal diseases.

Molecular Profile and the Effectiveness of Antimicrobials Drugs Against Staphylococcus aureus and Pseudomonas aeruginosa in the Diagnostic Approaches of Otitis Infection

Background

Otitis externa and otitis media are two types of ear infections that affect people of all ages, although they are more common in newborns and young children. Antibiotic usage, healthcare, and advanced age all play a role in the development of this illness.

Methods

Fifty-eight patients with various kinds of infections of the ears were voluntary patients attending the outpatient clinics of the Prince Mutaib Bin Abdulaziz Hospital in Sakaka, Al Jouf, Saudi Arabia, examined to evaluate the role of bacteria and the likely significance of plasmids in their antibiotic resistance as ear infectious agents.

Results

Staphylococcus aureus and Pseudomonas aeruginosa are the most prevalent bacteria found in ear infections. The greatest number of major bacterial isolates were S. aureus (54%), followed by P. aeruginosa (13%), whereas a smaller number of isolates (3%) were from Streptococcus pyogenes, Bacillus subtilis, and Proteus vulgaris, respectively. Mixed growth was noted in 3.4% of instances. The isolation rate for Gram-positive organisms was 72%, while the rate for Gram-negative species was 28%. All the isolates had DNA greater than 14 kilobases. Hind III analysis of the plasmid DNA extracted from the resistant strains of ear infection demonstrated that antibiotic-resistance plasmids were extensively dispersed. Exotoxin A PCR amplification indicated 396 pb PCR-positive DNA for all identified samples, with the exception of three strains for which no band was observed. Patients in the epidemiological study ranged in number, but all were linked together for the purposes of the study because of their shared epidemiological characteristics.

Conclusion

Vancomycin, linezolid, tigecycline, rifampin, and daptomycin are all antibiotics that have been shown to be effective against S. aureus and P. aeruginosa. Microbiological pattern evaluation and antibiotic sensitivity patterns of the microorganisms providing empirical antibiotics are becoming increasingly crucial to minimize issues and the development of antibiotic-resistant strains.

Cryo-EM of the Yeast VO Complex Reveals Distinct Binding Sites for Macrolide V-ATPase Inhibitors

Vacuolar-type adenosine triphosphatases (V-ATPases) are proton pumps found in almost all eukaryotic cells. These enzymes consist of a soluble catalytic V₁ region that hydrolyzes ATP and a membrane-embedded V_O region responsible for proton translocation. V-ATPase activity leads to acidification of endosomes, phagosomes, lysosomes, secretory vesicles, and the trans-Golgi network, with extracellular acidification occurring in some specialized cells. Small-molecule inhibitors of V-ATPase have played a crucial role in elucidating numerous aspects of cell biology by blocking acidification of intracellular compartments, while therapeutic use of V-ATPase inhibitors has been proposed for the treatment of cancer, osteoporosis, and some infections. Here, we determine structures of the isolated V_O complex from Saccharomyces cerevisiae bound to two well-known macrolide inhibitors: bafilomycin A1 and archazolid A. The structures reveal different binding sites for the inhibitors on the surface of the proton-carrying c ring, with only a small amount of overlap between the two sites. Binding of both inhibitors is mediated primarily through van der Waals interactions in shallow pockets and suggests that the inhibitors block rotation of the ring. Together, these structures indicate the existence of a large chemical space available for V-ATPase inhibitors that block acidification by binding the c ring.

Geraniol and Citral as potential therapeutic agents targeting the HSP90 activity: An in silico and experimental approach

Lemongrass essential oil has antifungal and anti-cancerous properties. Heat-shock protein (HSP90), an ATP-dependent molecular chaperone found in eukaryotes, is involved in protein folding, stability, and disease, making it a promising research topic. Both in silico and in vitro approaches were used to provide a clear insight into the HSP90-ATPase 3D structures, activity, and their interaction with the essential oil constituents among various species such as fungi (S. cerevisiae), parasites (P. falciparum), and humans. For in silico studies, sequence alignment, docking (AutoDock), and absorption, distribution, metabolism, and excretion (ADME) properties were evaluated to obtain hit compounds specifically against each HSP90-ATPase. The hit compounds obtained were evaluated for their efficacy in the in vitro studies of S. cerevisiae. In vitro studies were carried out targeting HSP90-ATPases via lemongrass essential oil components individually and in combination as a function of concentration and various salt concentrations. Results suggest that sequence alignment exists of over 75% among these three species. The best docking score was possessed by Geraniol and its constituent (geldanamycin ≥ -4.93 kcal/mol) (a known antifungal and antitumor against HSP90) in all the above species. Lemongrass oil and the combination of Geraniol and Citral at concentrations of 80 μg/mL showed the maximum inhibition of ATPase and HSP90-ATPase activity compared to their individual treatment. Therefore, both in silico and in vitro studies provide clear evidence of specific inhibitory action of lemongrass oil, Geraniol, and Citral against the ATPase and HSP90-ATPase activities and might show potential as antifungal and antitumor drugs.

Anti-oomycetes and immunostimulatory activity of natural plant extract compounds against Saprolegnia spp.: Molecular docking and in-vitro studies

This study aimed to investigate the effectiveness of five natural plant extract compounds Curcumin (CUR); Eugenol (EUG), Cinnamaldehyde (CIN), Stigmasterol (ST) and Morin (MOR), on two species of Saprolegnia; Saprolegnia parasitica and S. australis. Selective compounds were screened for the minimum inhibitory concentration, first for anti-oomycetes activity and then mycelium growth inhibition, spore germination inhibition and colonisation test. Nitric oxide production and myeloperoxidase activity of the compounds were tested in head kidney leukocytes of rainbow trout, Oncorhynchus mykiss to assess the immunostimulatory potential. Molecular docking of effective compounds was carried out with effector proteins of S. parasitica to investigate the target binding sites. Among all, CUR could completely inhibit zoospore production and significantly (p ≤ .05) inhibit hyphal growth at 16 mg l^-1 against S. parasitica and S. australis. CIN at the concentration of 50 mg l^-1 completely inhibited hyphal growth of both Saprolegnia spp., although the zoospore production of S. parasitica and S. australis was reduced at 25 mg l^-1 and 10 mg l^-1. In the case of EUG, significant inhibition of the hyphal growth and germination of S. parasitica zoospores was observed at 50 mg l^-1. ST and MOR did not show antioomycetes activity. The molecular docking results were consistent with in vitro studies, possibly due to the binding with the vital proteins (Plasma membrane ATPase, V-type proton ATPase, TKL protein kinase, Host targeting protein 1) of S. parasitica and ultimately inhibiting their activity. CUR and CIN showed increased nitric oxide production at the highest concentration of 250 and 256 mg l^-1 but the value was not significant (p ≤ .05) with control. CUR showed significantly higher peroxidase activity (p ≤ .05) at a concentration of 256 mg l^-1 though values were significantly similar with concentration from 16 to 128 mg l^-1. The nitric oxide and total peroxidase activity of rainbow trout leukocytes in the case of CIN showed a significant difference only at 250 mg l^-1 against the control. The results conclude that CUR, CIN showed the better anti-Saprolegnia activity and could be used as phyto-additives in aquaculture. Among all, the inclusion of CUR as phyto-additives will provide additional immunostimulatory activity.

The V-ATPase regulates localization of the TRP Ca2+ channel Yvc1 in response to oxidative stress in Candida albicans

The vacuolar-type H⁺-ATPase (V-ATPase) is a highly conserved protein complex among the eukaryotic cells. We previously revealed that both the V-ATPase and the transient receptor potential (TRP) channel Yvc1 are involved in oxidative stress response (OSR). However, the relationship between V-ATPase and Yvc1 during OSR remains unknown. In this study, disruption of the V-ATPase-encoding genes VPH2 and TFP1, similar with disruption of YVC1, caused H₂O₂ hypersensitivity and enhancement of vacuolar membrane permeability (VMP) under oxidative stress. Further investigations showed that unlike the wild type strain with vacuole membrane-localized Yvc1, both vph2Δ/Δ and tfp1Δ/Δ had Yvc1 localization in the vacuole cavity, indicating that disruption of VPH2 or TFP1 impaired normal vacuolar membrane-localization of Yvc1. Interestingly, addition of CaCl₂ alleviated the growth defect of vph2Δ/Δ and tfp1Δ/Δ under oxidative stress, leading to prevention of VMP, decrease in ROS levels and activation of OSR. In contrast, addition of the Ca²⁺ chelating agent glycol-bis-(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) aggravated H₂O₂ hypersensitivity of the mutants. These results showed that the V-ATPase plays an important role in maintenance of normal Yvc1 localization, which contributes to Ca²⁺ transport from the vacuoles to the cytosol for activation of OSR. This work sheds a novel light on the interaction between V-ATPase and Ca²⁺ transport for regulation of OSR in C. albicans.

The Role of Secretory Pathways in Candida albicans Pathogenesis

Candida albicans is a fungus that is a commensal organism and a member of the normal human microbiota. It has the ability to transition into an opportunistic invasive pathogen. Attributes that support pathogenesis include secretion of virulence-associated proteins, hyphal formation, and biofilm formation. These processes are supported by secretion, as defined in the broad context of membrane trafficking. In this review, we examine the role of secretory pathways in Candida virulence, with a focus on the model opportunistic fungal pathogen, Candida albicans.

Vacuolar proton-translocating ATPase is required for antifungal resistance and virulence of Candida glabrata

Vacuolar proton-translocating ATPase (V-ATPase) is located in fungal vacuolar membranes. It is involved in multiple cellular processes, including the maintenance of intracellular ion homeostasis by maintaining acidic pH within the cell. The importance of V-ATPase in virulence has been demonstrated in several pathogenic fungi, including Candida albicans. However, it remains to be determined in the clinically important fungal pathogen Candida glabrata. Increasing multidrug resistance of C. glabrata is becoming a critical issue in the clinical setting. In the current study, we demonstrated that the plecomacrolide V-ATPase inhibitor bafilomycin B₁ exerts a synergistic effect with azole antifungal agents, including fluconazole and voriconazole, against a C. glabrata wild-type strain. Furthermore, the deletion of the VPH2 gene encoding an assembly factor of V-ATPase was sufficient to interfere with V-ATPase function in C. glabrata, resulting in impaired pH homeostasis in the vacuole and increased sensitivity to a variety of environmental stresses, such as alkaline conditions (pH 7.4), ion stress (Na⁺, Ca²⁺, Mn²⁺, and Zn²⁺ stress), exposure to the calcineurin inhibitor FK506 and antifungal agents (azoles and amphotericin B), and iron limitation. In addition, virulence of C. glabrata Δvph2 mutant in a mouse model of disseminated candidiasis was reduced in comparison with that of the wild-type and VPH2-reconstituted strains. These findings support the notion that V-ATPase is a potential attractive target for the development of effective antifungal strategies.

Atovaquone Impairs Growth of Aspergillus and Fusarium Keratitis Isolates by Modulating Mitochondrial Function and Zinc Homeostasis

Purpose

Aspergillus and Fusarium molds cause blinding corneal infections as a consequence of ocular trauma and in association with contact lens wear. As these fungi require zinc for fungal growth, we examined the effect of atovaquone, a ubiquinone analog that disrupts zinc homeostasis, on fungal growth in vitro and in vivo.

Methods

In vitro: Aspergillus and Fusarium germinating conidia were incubated overnight with atovaquone, and hyphal growth was measured by fluorimetry. In vivo: C57BL/6 mouse corneas were infected with Aspergillus or Fusarium conidia. Atovaquone was added topically and corneal opacification and fungal growth were quantified.

Results

Atovaquone has antifungal activity against Aspergillus and Fusarium clinical isolates, with Fusarium species being more sensitive to atovaquone than Aspergillus species. Atovaquone also reduced labile intracellular zinc levels and increased the sensitivity of Aspergillus to metal shock. Atovaquone reduced vacuolar acidification, which regulates storage of intracellular free zinc, and also acted synergistically with voriconazole and itraconazole to kill hyphae. Furthermore, mitochondrial potential and ATP production were reduced in both Aspergillus and Fusarium following atovaquone treatment. Finally, topical application of atovaquone to the ocular surface significantly inhibited fungal growth and corneal opacification in murine models of fungal keratitis.

Conclusions

These studies demonstrate that atovaquone has pronounced in vitro and in vivo antifungal activity against filamentous fungi by disrupting both metal homeostasis and mitochondrial function, and therefore has potential as a novel antifungal agent.

FcRav2, a gene with a ROGDI domain involved in Fusarium head blight and crown rot on durum wheat caused by Fusarium culmorum

Fusarium culmorum is a soil-borne fungal pathogen which causes foot and root rot and Fusarium head blight on small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in the contamination of kernels with type B trichothecene mycotoxins. Our knowledge of the pathogenicity factors of this fungus is still limited. A transposon tagging approach based on the mimp1/impala double-component system has allowed us to select a mutant altered in multiple metabolic and morphological processes, trichothecene production and virulence. The flanking regions of mimp1 were used to seek homologies in the F. culmorum genome, and revealed that mimp1 had reinserted within the last exon of a gene encoding a hypothetical protein of 318 amino acids which contains a ROGDI-like leucine zipper domain, supposedly playing a protein-protein interaction or regulatory role. By functional complementation and bioinformatic analysis, we characterized the gene as the yeast Rav2 homologue, confirming the high level of divergence in multicellular fungi. Deletion of FcRav2 or its orthologous gene in F. graminearum highlighted its ability to influence a number of functions, including virulence, trichothecene type B biosynthesis, resistance to azoles and resistance to osmotic and oxidative stress. Our results indicate that the FcRav2 protein (and possibly the RAVE complex as a whole) may become a suitable target for new antifungal drug development or the plant-mediated resistance response in filamentous fungi of agricultural interest.

NaCl-induced expression of AtVHA-c5 gene in the roots plays a role in response of Arabidopsis to salt stress

Suppression of AtVHA-c5 expression results in changes in H⁺ and Na⁺ fluxes of roots, and increase sensitivity to salt in Arabidopsis. Vacuolar-type H⁺-ATPase (V-ATPase), a multisubunit endomembrane proton pump, is essential in plant growth and response to environmental stresses. In the present study, the function of Arabidopsis V-ATPase subunit c5 (AtVHA-c5) gene in response to salt stress was investigated. Subcellular localization showed that AtVHA-c5 was mainly localized to endosomes and the vacuolar membrane in Arabidopsis. The analysis of quantitative real-time PCR showed that expression of AtVHA-c5 gene was induced by NaCl stress. Histochemical analysis revealed that AtVHA-c5 was expressed in the root epidermis of untreated Arabidopsis and in the whole root elongation zone after NaCl treatment. Phenotypic analysis showed that the atvha-c5 mutant is sensitive to high NaCl as compared to the wild type. The non-invasive micro-test technology measurement demonstrated that the net H⁺ and Na⁺ efflux in the root elongation zone of the atvha-c5 mutant was weaker than that of the wild type under NaCl treatment, suggesting that H⁺ and Na⁺ fluxes in atvha-c5 roots are impaired under NaCl stress. Moreover, compared to the wild type, the expression of AtSOS1 (salt overly sensitive 1) and AtAHA1 (plasma membrane H⁺-ATPase 1) were down-regulated in atvha-c5 roots under NaCl stress. Overall, our results indicate that AtVHA-c5 plays a role in Arabidopsis root response to NaCl stress by influencing H⁺ and Na⁺ fluxes.

Contribution of VMA5 to vacuolar function, stress response, ion homeostasis and autophagy in Candida albicans

AIM

V-ATPase is a conservative multi-subunit enzyme in eukaryotes and modulates several cellular responses. This study aimed to illustrate the roles of Vma5 in vacuolar function, oxidative stress response, calcium homeostasis, autophagy and virulence.

MATERIALS & METHODS

The vma5Δ/Δ mutant was obtained using PCR-mediated homologous recombination. The functions of Vma5 were investigated by a series of biochemical and systemic infection methods.

RESULTS

Disruption of VMA5 led to growth inhibition, vacuolar dysfunction, disturbance of calcium homeostasis and inhibition of calcium-related oxidative stress response. Furthermore, its deletion caused defects in autophagy completion and hyphal development, and resulted in attenuated Candida albicans virulence.

CONCLUSION

Our findings provide new insights into V-ATPase functions in C. albicans, and reveal a potential candidate for development of antifungal drugs.

Rotation Mechanism of Molecular Motor V1-ATPase Studied by Multiscale Molecular Dynamics Simulation

Enterococcus hirae V₁-ATPase is a molecular motor composed of the A₃B₃ hexamer ring and the central stalk. In association with ATP hydrolysis, three catalytic AB pairs in the A₃B₃ ring undergo conformational changes, which lead to a 120° rotation of the central stalk. To understand how the conformational changes of three catalytic pairs induce the 120° rotation of the central stalk, we performed multiscale molecular dynamics (MD) simulations in which coarse-grained and all-atom MD simulations were combined using a fluctuation matching methodology. During the rotation, a catalytic AB pair spontaneously adopted an intermediate conformation, which was not included in the initial inputs of the simulations and was essentially close to the “bindable-like” structure observed in a recently solved crystal structure. Furthermore, the creation of a space between the bindable-like and tight pairs was required for the central stalk to rotate without steric hindrance. These cooperative rearrangements of the three catalytic pairs are crucial for the rotation of the central stalk.

Proton Transport and pH Control in Fungi

Despite diverse and changing extracellular environments, fungi maintain a relatively constant cytosolic pH and numerous organelles of distinct lumenal pH. Key players in fungal pH control are V-ATPases and the P-type proton pump Pma1. These two proton pumps act in concert with a large array of other transporters and are highly regulated. The activities of Pma1 and the V-ATPase are coordinated under some conditions, suggesting that pH in the cytosol and organelles is not controlled independently. Genomic studies, particularly in the highly tractable S. cerevisiae, are beginning to provide a systems-level view of pH control, including transcriptional responses to acid or alkaline ambient pH and definition of the full set of regulators required to maintain pH homeostasis. Genetically encoded pH sensors have provided new insights into localized mechanisms of pH control, as well as highlighting the dynamic nature of pH responses to the extracellular environment. Recent studies indicate that cellular pH plays a genuine signaling role that connects nutrient availability and growth rate through a number of mechanisms. Many of the pH control mechanisms found in S. cerevisiae are shared with other fungi, with adaptations for their individual physiological contexts. Fungi deploy certain proton transport and pH control mechanisms not shared with other eukaryotes; these regulators of cellular pH are potential antifungal targets. This review describes current and emerging knowledge proton transport and pH control mechanisms in S. cerevisiae and briefly discusses how these mechanisms vary among fungi.

Identification of Additional Anti-Persister Activity against Borrelia burgdorferi from an FDA Drug Library

Lyme disease is a leading vector-borne disease in the United States. Although the majority of Lyme patients can be cured with standard 2–4 week antibiotic treatment, 10%–20% of patients continue to suffer from prolonged post-treatment Lyme disease syndrome (PTLDS). While the cause for this is unclear, persisting organisms not killed by current Lyme antibiotics may be involved. In our previous study, we screened an FDA drug library and reported 27 top hits that showed high activity against Borrelia persisters. In this study, we present the results of an additional 113 active hits that have higher activity against the stationary phase B. burgdorferi than the currently used Lyme antibiotics. Many antimicrobial agents (antibiotics, antivirals, antifungals, anthelmintics or antiparasitics) used for treating other infections were found to have better activity than the current Lyme antibiotics. These include antibacterials such as rifamycins (3-formal-rifamycin, rifaximin, rifamycin SV), thiostrepton, quinolone drugs (sarafloxacin, clinafloxacin, tosufloxacin), and cell wall inhibitors carbenicillin, tazobactam, aztreonam; antifungal agents such as fluconazole, mepartricin, bifonazole, climbazole, oxiconazole, nystatin; antiviral agents zanamivir, nevirapine, tilorone; antimalarial agents artemisinin, methylene blue, and quidaldine blue; antihelmintic and antiparasitic agents toltrazuril, tartar emetic, potassium antimonyl tartrate trihydrate, oxantel, closantel, hycanthone, pyrimethamine, and tetramisole. Interestingly, drugs used for treating other non-infectious conditions including verteporfin, oltipraz, pyroglutamic acid, pidolic acid, and dextrorphan tartrate, that act on the glutathione/γ-glutamyl pathway involved in protection against free radical damage, and also the antidepressant drug indatraline, were found to have high activity against stationary phase B. burgdorferi. Among the active hits, agents that affect cell membranes, energy production, and reactive oxygen species production are more active against the B. burgdorferi persisters than the commonly used antibiotics that inhibit macromolecule biosynthesis. Future studies are needed to evaluate and optimize the promising active hits in drug combination studies in vitro and also in vivo in animal models. These studies may have implications for developing more effective treatments of Lyme disease.

The contribution of Candida albicans vacuolar ATPase subunit V₁B, encoded by VMA2, to stress response, autophagy, and virulence is independent of environmental pH

Candida albicans vacuoles are central to many critical biological processes, including filamentation and in vivo virulence. The V-ATPase proton pump is a multisubunit complex responsible for organellar acidification and is essential for vacuolar biogenesis and function. To study the function of the V₁B subunit of C. albicans V-ATPase, we constructed a tetracycline-regulatable VMA2 mutant, tetR-VMA2. Inhibition of VMA2 expression resulted in the inability to grow at alkaline pH and altered resistance to calcium, cold temperature, antifungal drugs, and growth on nonfermentable carbon sources. Furthermore, V-ATPase was unable to fully assemble at the vacuolar membrane and was impaired in proton transport and ATPase-specific activity. VMA2 repression led to vacuolar alkalinization in addition to abnormal vacuolar morphology and biogenesis. Key virulence-related traits, including filamentation and secretion of degradative enzymes, were markedly inhibited. These results are consistent with previous studies of C. albicans V-ATPase; however, differential contributions of the V-ATPase Vo and V₁ subunits to filamentation and secretion are observed. We also make the novel observation that inhibition of C. albicans V-ATPase results in increased susceptibility to osmotic stress. Notably, V-ATPase inhibition under conditions of nitrogen starvation results in defects in autophagy. Lastly, we show the first evidence that V-ATPase contributes to virulence in an acidic in vivo system by demonstrating that the tetR-VMA2 mutant is avirulent in a Caenorhabditis elegans infection model. This study illustrates the fundamental requirement of V-ATPase for numerous key virulence-related traits in C. albicans and demonstrates that the contribution of V-ATPase to virulence is independent of host pH.

Saccharomyces cerevisiae vacuolar H+-ATPase regulation by disassembly and reassembly: one structure and multiple signals

Vacuolar H(+)-ATPases (V-ATPases) are highly conserved ATP-driven proton pumps responsible for acidification of intracellular compartments. V-ATPase proton transport energizes secondary transport systems and is essential for lysosomal/vacuolar and endosomal functions. These dynamic molecular motors are composed of multiple subunits regulated in part by reversible disassembly, which reversibly inactivates them. Reversible disassembly is intertwined with glycolysis, the RAS/cyclic AMP (cAMP)/protein kinase A (PKA) pathway, and phosphoinositides, but the mechanisms involved are elusive. The atomic- and pseudo-atomic-resolution structures of the V-ATPases are shedding light on the molecular dynamics that regulate V-ATPase assembly. Although all eukaryotic V-ATPases may be built with an inherent capacity to reversibly disassemble, not all do so. V-ATPase subunit isoforms and their interactions with membrane lipids and a V-ATPase-exclusive chaperone influence V-ATPase assembly. This minireview reports on the mechanisms governing reversible disassembly in the yeast Saccharomyces cerevisiae, keeping in perspective our present understanding of the V-ATPase architecture and its alignment with the cellular processes and signals involved.

Attenuation of Candida albicans virulence with focus on disruption of its vacuole functions

The objective of the present review is to discuss if the yeast vacuole can be used as a target for attenuation of Candida albicans virulence. Literature searches were made electronically using predetermined inclusion criteria. The main searches were made through a systematic strategy in PubMed and authoritative journals in microbiology. It appeared that C. albicans virulence may be reduced by inhibiting vacuolar proton-translocating ATPase (V-ATPase) functions and acidification of the yeast vacuole by V-ATPase inhibitors, by seeking the synergistic effect of antifungals and non-antifungals affecting yeast vacuolar functions, and by inhibiting filament production – also regulated by the vacuole. Accordingly, we may impair C. albicans virulence by inhibiting functions of its vacuole, which plays essential roles during colonization and invasion of the host. Except for drugs where indications for clinical use can be redefined, such interventions may be closer to theory than to reality at the moment. But since the yeast is so difficult to eradicate by antifungal treatment, it could be rewarding to seek new strategies for reducing its virulence rather than trying to eradicate it completely from the microbiota, which often turns out to be impossible.