A highly conserved tRNA modification contributes to C. albicans filamentation and virulence

tRNA modifications play important roles in maintaining translation accuracy in all domains of life. Disruptions in the tRNA modification machinery, especially of the anticodon stem loop, can be lethal for many bacteria and lead to a broad range of phenotypes in baker's yeast. Very little is known about the function of tRNA modifications in host-pathogen interactions, where rapidly changing environments and stresses require fast adaptations. We found that two closely related fungal pathogens of humans, the highly pathogenic Candida albicans and its much less pathogenic sister species, Candida dubliniensis, differ in the function of a tRNA-modifying enzyme. This enzyme, Hma1, exhibits species-specific effects on the ability of the two fungi to grow in the hypha morphology, which is central to their virulence potential. We show that Hma1 has tRNA-threonylcarbamoyladenosine dehydratase activity, and its deletion alters ribosome occupancy, especially at 37°C-the body temperature of the human host. A C. albicans HMA1 deletion mutant also shows defects in adhesion to and invasion into human epithelial cells and shows reduced virulence in a fungal infection model. This links tRNA modifications to host-induced filamentation and virulence of one of the most important fungal pathogens of humans.IMPORTANCEFungal infections are on the rise worldwide, and their global burden on human life and health is frequently underestimated. Among them, the human commensal and opportunistic pathogen, Candida albicans, is one of the major causative agents of severe infections. Its virulence is closely linked to its ability to change morphologies from yeasts to hyphae. Here, this ability is linked-to our knowledge for the first time-to modifications of tRNA and translational efficiency. One tRNA-modifying enzyme, Hma1, plays a specific role in C. albicans and its ability to invade the host. This adds a so-far unknown layer of regulation to the fungal virulence program and offers new potential therapeutic targets to fight fungal infections.

Nanobody-mediated neutralization of candidalysin prevents epithelial damage and inflammatory responses that drive vulvovaginal candidiasis pathogenesis

Candida albicans can cause mucosal infections in humans. This includes oropharyngeal candidiasis, which is commonly observed in human immunodeficiency virus infected patients, and vulvovaginal candidiasis (VVC), which is the most frequent manifestation of candidiasis. Epithelial cell invasion by C. albicans hyphae is accompanied by the secretion of candidalysin, a peptide toxin that causes epithelial cell cytotoxicity. During vaginal infections, candidalysin-driven tissue damage triggers epithelial signaling pathways, leading to hyperinflammatory responses and immunopathology, a hallmark of VVC. Therefore, we proposed blocking candidalysin activity using nanobodies to reduce epithelial damage and inflammation as a therapeutic strategy for VVC. Anti-candidalysin nanobodies were confirmed to localize around epithelial-invading C. albicans hyphae, even within the invasion pocket where candidalysin is secreted. The nanobodies reduced candidalysin-induced damage to epithelial cells and downstream proinflammatory responses. Accordingly, the nanobodies also decreased neutrophil activation and recruitment. In silico mathematical modeling enabled the quantification of epithelial damage caused by candidalysin under various nanobody dosing strategies. Thus, nanobody-mediated neutralization of candidalysin offers a novel therapeutic approach to block immunopathogenic events during VVC and alleviate symptoms.IMPORTANCEWorldwide, vaginal infections caused by Candida albicans (VVC) annually affect millions of women, with symptoms significantly impacting quality of life. Current treatments are based on anti-fungals and probiotics that target the fungus. However, in some cases, infections are recurrent, called recurrent VVC, which often fails to respond to treatment. Vaginal mucosal tissue damage caused by the C. albicans peptide toxin candidalysin is a key driver in the induction of hyperinflammatory responses that fail to clear the infection and contribute to immunopathology and disease severity. In this pre-clinical evaluation, we show that nanobody-mediated candidalysin neutralization reduces tissue damage and thereby limits inflammation. Implementation of candidalysin-neutralizing nanobodies may prove an attractive strategy to alleviate symptoms in complicated VVC cases.

Secretion of the fungal toxin candidalysin is dependent on conserved precursor peptide sequences

The opportunistic fungal pathogen Candida albicans damages host cells via its peptide toxin, candidalysin. Before secretion, candidalysin is embedded in a precursor protein, Ece1, which consists of a signal peptide, the precursor of candidalysin and seven non-candidalysin Ece1 peptides (NCEPs), and is found to be conserved in clinical isolates. Here we show that the Ece1 polyprotein does not resemble the usual precursor structure of peptide toxins. C. albicans cells are not susceptible to their own toxin, and single NCEPs adjacent to candidalysin are sufficient to prevent host cell toxicity. Using a series of Ece1 mutants, mass spectrometry and anti-candidalysin nanobodies, we show that NCEPs play a role in intracellular Ece1 folding and candidalysin secretion. Removal of single NCEPs or modifications of peptide sequences cause an unfolded protein response (UPR), which in turn inhibits hypha formation and pathogenicity in vitro. Our data indicate that the Ece1 precursor is not required to block premature pore-forming toxicity, but rather to prevent intracellular auto-aggregation of candidalysin sequences.

Candida albicans translocation through the intestinal epithelial barrier is promoted by fungal zinc acquisition and limited by NFκB-mediated barrier protection

The opportunistic fungal pathogen Candida albicans thrives on human mucosal surfaces as a harmless commensal, but frequently causes infections under certain predisposing conditions. Translocation across the intestinal barrier into the bloodstream by intestine-colonizing C. albicans cells serves as the main source of disseminated candidiasis. However, the host and microbial mechanisms behind this process remain unclear. In this study we identified fungal and host factors specifically involved in infection of intestinal epithelial cells (IECs) using dual-RNA sequencing. Our data suggest that host-cell damage mediated by the peptide toxin candidalysin-encoding gene ECE1 facilitates fungal zinc acquisition. This in turn is crucial for the full virulence potential of C. albicans during infection. IECs in turn exhibit a filamentation- and damage-specific response to C. albicans infection, including NFκB, MAPK, and TNF signaling. NFκB activation by IECs limits candidalysin-mediated host-cell damage and mediates maintenance of the intestinal barrier and cell-cell junctions to further restrict fungal translocation. This is the first study to show that candidalysin-mediated damage is necessary for C. albicans nutrient acquisition during infection and to explain how IECs counteract damage and limit fungal translocation via NFκB-mediated maintenance of the intestinal barrier.

The hyphal-specific toxin candidalysin promotes fungal gut commensalism

The fungus Candida albicans frequently colonizes the human gastrointestinal tract, from which it can disseminate to cause systemic disease. This polymorphic species can transition between growing as single-celled yeast and as multicellular hyphae to adapt to its environment. The current dogma of C. albicans commensalism is that the yeast form is optimal for gut colonization, whereas hyphal cells are detrimental to colonization but critical for virulence1-3. Here, we reveal that this paradigm does not apply to multi-kingdom communities in which a complex interplay between fungal morphology and bacteria dictates C. albicans fitness. Thus, whereas yeast-locked cells outcompete wild-type cells when gut bacteria are absent or depleted by antibiotics, hyphae-competent wild-type cells outcompete yeast-locked cells in hosts with replete bacterial populations. This increased fitness of wild-type cells involves the production of hyphal-specific factors including the toxin candidalysin4,5, which promotes the establishment of colonization. At later time points, adaptive immunity is engaged, and intestinal immunoglobulin A preferentially selects against hyphal cells1,6. Hyphal morphotypes are thus under both positive and negative selective pressures in the gut. Our study further shows that candidalysin has a direct inhibitory effect on bacterial species, including limiting their metabolic output. We therefore propose that C. albicans has evolved hyphal-specific factors, including candidalysin, to better compete with bacterial species in the intestinal niche.

From environmental adaptation to host survival: Attributes that mediate pathogenicity of Candida auris

Candida species are a major cause of invasive fungal infections. While Candida albicans, C. glabrata, C. parapsilosis, and C. tropicalis are the most dominant species causing life-threatening candidiasis, C. auris recently emerged as a new species causing invasive infections with high rates of clinical treatment failures. To mimic initial phases of systemic Candida infections with dissemination via the bloodstream and to elucidate the pathogenic potential of C. auris, we used an ex vivo whole blood infection model. Similar to other clinically relevant Candida spp., C. auris is efficiently killed in human blood, but showed characteristic patterns of immune cell association, survival rates, and cytokine induction. Dual-species transcriptional profiling of C. auris-infected blood revealed a unique C. auris gene expression program during infection, while the host response proofed similar and conserved compared to other Candida species. C. auris-specific responses included adaptation and survival strategies, such as counteracting oxidative burst of immune cells, but also expression of potential virulence factors, (drug) transporters, and cell surface-associated genes. Despite comparable pathogenicity to other Candida species in our model, C. auris-specific transcriptional adaptations as well as its increased stress resistance and long-term environmental survival, likely contribute to the high risk of contamination and distribution in a nosocomial setting. Moreover, infections of neutrophils with pre-starved C. auris cells suggest that environmental preconditioning can have modulatory effects on the early host interaction. In summary, we present novel insights into C. auris pathogenicity, revealing adaptations to human blood and environmental niches distinctive from other Candida species.

Calcium-dependent ESCRT recruitment and lysosome exocytosis maintain epithelial integrity during Candida albicans invasion

Candida albicans is both a commensal and an opportunistic fungal pathogen. Invading hyphae of C. albicans secrete candidalysin, a pore-forming peptide toxin. To prevent cell death, epithelial cells must protect themselves from direct damage induced by candidalysin and by the mechanical forces exerted by expanding hyphae. We identify two key Ca2+-dependent repair mechanisms employed by epithelial cells to withstand candidalysin-producing hyphae. Using camelid nanobodies, we demonstrate candidalysin secretion directly into the invasion pockets induced by elongating C. albicans hyphae. The toxin induces oscillatory increases in cytosolic [Ca2+], which cause hydrolysis of PtdIns(4,5)P2 and loss of cortical actin. Epithelial cells dispose of damaged membrane regions containing candidalysin by an Alg-2/Alix/ESCRT-III-dependent blebbing process. At later stages, plasmalemmal tears induced mechanically by invading hyphae are repaired by exocytic insertion of lysosomal membranes. These two repair mechanisms maintain epithelial integrity and prevent mucosal damage during both commensal growth and infection by C. albicans.

A variant ECE1 allele contributes to reduced pathogenicity of Candida albicans during vulvovaginal candidiasis

Vulvovaginal candidiasis (VVC), caused primarily by the human fungal pathogen Candida albicans, results in significant quality-of-life issues for women worldwide. Candidalysin, a toxin derived from a polypeptide (Ece1p) encoded by the ECE1 gene, plays a crucial role in driving immunopathology at the vaginal mucosa. This study aimed to determine if expression and/or processing of Ece1p differs across C. albicans isolates and whether this partly underlies differential pathogenicity observed clinically. Using a targeted sequencing approach, we determined that isolate 529L harbors a similarly expressed, yet distinct Ece1p isoform variant that encodes for a predicted functional candidalysin; this isoform was conserved amongst a collection of clinical isolates. Expression of the ECE1 open reading frame (ORF) from 529L in an SC5314-derived ece1Δ/Δ strain resulted in significantly reduced vaginopathogenicity as compared to an isogenic control expressing a wild-type (WT) ECE1 allele. However, in vitro challenge of vaginal epithelial cells with synthetic candidalysin demonstrated similar toxigenic activity amongst SC5314 and 529L isoforms. Creation of an isogenic panel of chimeric strains harboring swapped Ece1p peptides or HiBiT tags revealed reduced secretion with the ORF from 529L that was associated with reduced virulence. A genetic survey of 78 clinical isolates demonstrated a conserved pattern between Ece1p P2 and P3 sequences, suggesting that substrate specificity around Kex2p-mediated KR cleavage sites involved in protein processing may contribute to differential pathogenicity amongst clinical isolates. Therefore, we present a new mechanism for attenuation of C. albicans virulence at the ECE1 locus.

Candidalysin delivery to the invasion pocket is critical for host epithelial damage induced by Candida albicans

The human pathogenic fungus Candida albicans is a frequent cause of mucosal infections. Although the ability to transition from the yeast to the hypha morphology is essential for virulence, hypha formation and host cell invasion per se are not sufficient for the induction of epithelial damage. Rather, the hypha-associated peptide toxin, candidalysin, a product of the Ece1 polyprotein, is the critical damaging factor. While synthetic, exogenously added candidalysin is sufficient to damage epithelial cells, the level of damage does not reach the same level as invading C. albicans hyphae. Therefore, we hypothesized that a combination of fungal attributes is required to deliver candidalysin to the invasion pocket to enable the full damaging potential of C. albicans during infection. Utilising a panel of C. albicans mutants with known virulence defects, we demonstrate that the full damage potential of C. albicans requires the coordinated delivery of candidalysin to the invasion pocket. This process requires appropriate epithelial adhesion, hyphal extension and invasion, high levels of ECE1 transcription, proper Ece1 processing and secretion of candidalysin. To confirm candidalysin delivery, we generated camelid V_H Hs (nanobodies) specific for candidalysin and demonstrate localization and accumulation of the toxin only in C. albicans-induced invasion pockets. In summary, a defined combination of virulence attributes and cellular processes is critical for delivering candidalysin to the invasion pocket to enable the full damage potential of C. albicans during mucosal infection. TAKE AWAYS: Candidalysin is a peptide toxin secreted by C. albicans causing epithelial damage. Candidalysin delivery to host cell membranes requires specific fungal attributes. Candidalysin accumulates in invasion pockets created by invasive hyphae. Camelid nanobodies enabled visualisation of candidalysin in the invasion pocket.

Fungal biotin homeostasis is essential for immune evasion after macrophage phagocytosis and virulence

Biotin is an important cofactor for multiple enzymes in central metabolic processes. While many bacteria and most fungi are able to synthesise biotin de novo, Candida spp. are auxotrophic for this vitamin and thus require efficient uptake systems to facilitate biotin acquisition during infection. Here we show that Candida glabrata and Candida albicans use a largely conserved system for biotin uptake and regulation, consisting of the high-affinity biotin transporter Vht1 and the transcription factor Vhr1. Both species induce expression of biotin-metabolic genes upon in vitro biotin depletion and following phagocytosis by macrophages, indicating low biotin levels in the Candida-containing phagosome. In line with this, we observed reduced intracellular proliferation of both Candida cells pre-starved of biotin and deletion mutants lacking VHR1 or VHT1 genes. VHT1 was essential for the full virulence of C. albicans during systemic mouse infections, and the lack of VHT1 led to reduced fungal burden in C. glabrata-infected brains and C. albicans-infected brains and kidneys. Together, our data suggest a critical role of Vht1-mediated biotin acquisition for C. glabrata and C. albicans during intracellular growth in macrophages and systemic infections.

Keeping Candida commensal: how lactobacilli antagonize pathogenicity of Candida albicans in an in vitro gut model

The intestine is the primary reservoir of Candida albicans that can cause systemic infections in immunocompromised patients. In this reservoir, the fungus exists as a harmless commensal. However, antibiotic treatment can disturb the bacterial microbiota, facilitating fungal overgrowth and favoring pathogenicity. The current in vitro gut models that are used to study the pathogenesis of C. albicans investigate the state in which C. albicans behaves as a pathogen rather than as a commensal. We present a novel in vitro gut model in which the fungal pathogenicity is reduced to a minimum by increasing the biological complexity. In this model, enterocytes represent the epithelial barrier and goblet cells limit C. albicans adhesion and invasion. Significant protection against C. albicans-induced necrotic damage was achieved by the introduction of a microbiota of antagonistic lactobacilli. We demonstrated a time-, dose- and species-dependent protective effect against C. albicans-induced cytotoxicity. This required bacterial growth, which relied on the presence of host cells, but was not dependent on the competition for adhesion sites. Lactobacillus rhamnosus reduced hyphal elongation, a key virulence attribute. Furthermore, bacterial-driven shedding of hyphae from the epithelial surface, associated with apoptotic epithelial cells, was identified as a main and novel mechanism of damage protection. However, host cell apoptosis was not the driving mechanism behind shedding. Collectively, we established an in vitro gut model that can be used to experimentally dissect commensal-like interactions of C. albicans with a bacterial microbiota and the host epithelial barrier. We also discovered fungal shedding as a novel mechanism by which bacteria contribute to the protection of epithelial surfaces.This article has an associated First Person interview with the joint first authors of the paper.

Candida albicans-Induced Epithelial Damage Mediates Translocation through Intestinal Barriers

Life-threatening systemic infections often occur due to the translocation of pathogens across the gut barrier and into the bloodstream. While the microbial and host mechanisms permitting bacterial gut translocation are well characterized, these mechanisms are still unclear for fungal pathogens such as Candida albicans, a leading cause of nosocomial fungal bloodstream infections. In this study, we dissected the cellular mechanisms of translocation of C. albicans across intestinal epithelia in vitro and identified fungal genes associated with this process. We show that fungal translocation is a dynamic process initiated by invasion and followed by cellular damage and loss of epithelial integrity. A screen of >2,000 C. albicans deletion mutants identified genes required for cellular damage of and translocation across enterocytes. Correlation analysis suggests that hypha formation, barrier damage above a minimum threshold level, and a decreased epithelial integrity are required for efficient fungal translocation. Translocation occurs predominantly via a transcellular route, which is associated with fungus-induced necrotic epithelial damage, but not apoptotic cell death. The cytolytic peptide toxin of C. albicans, candidalysin, was found to be essential for damage of enterocytes and was a key factor in subsequent fungal translocation, suggesting that transcellular translocation of C. albicans through intestinal layers is mediated by candidalysin. However, fungal invasion and low-level translocation can also occur via non-transcellular routes in a candidalysin-independent manner. This is the first study showing translocation of a human-pathogenic fungus across the intestinal barrier being mediated by a peptide toxin.IMPORTANCECandida albicans, usually a harmless fungus colonizing human mucosae, can cause lethal bloodstream infections when it manages to translocate across the intestinal epithelium. This can result from antibiotic treatment, immune dysfunction, or intestinal damage (e.g., during surgery). However, fungal processes may also contribute. In this study, we investigated the translocation process of C. albicans using in vitro cell culture models. Translocation occurs as a stepwise process starting with invasion, followed by epithelial damage and loss of epithelial integrity. The ability to secrete candidalysin, a peptide toxin deriving from the hyphal protein Ece1, is key: C. albicans hyphae, secreting candidalysin, take advantage of a necrotic weakened epithelium to translocate through the intestinal layer.

The Snf1-activating kinase Sak1 is a key regulator of metabolic adaptation and in vivo fitness of Candida albicans

The metabolic flexibility of the opportunistic fungal pathogen Candida albicans is important for colonisation and infection of different host niches. Complex regulatory networks, in which protein kinases play central roles, link metabolism and other virulence-associated traits, such as filamentous growth and stress resistance, and thereby control commensalism and pathogenicity. By screening a protein kinase deletion mutant library that was generated in the present work using an improved SAT1 flipper cassette, we found that the previously uncharacterised kinase Sak1 is a key upstream activator of the protein kinase Snf1, a highly conserved regulator of nutrient stress responses that is essential for viability in C. albicans. The sak1Δ mutants failed to grow on many alternative carbon sources and were hypersensitive to cell wall/membrane stress. These phenotypes were mirrored in mutants lacking other subunits of the SNF1 complex and partially compensated by a hyperactive form of Snf1. Transcriptional profiling of sak1Δ mutants showed that Sak1 ensures basal expression of glyoxylate cycle and gluconeogenesis genes even in glucose-rich media and thereby contributes to the metabolic plasticity of C. albicans. In a mouse model of gastrointestinal colonisation, sak1Δ mutants were rapidly outcompeted by wild-type cells, demonstrating that Sak1 is essential for the in vivo fitness of C. albicans.

[What went wrong? Analysis of Medical Malpractice Arbitration Proceedings Conducted by a German Arbitration Board after Breast Reductions]

INTRODUCTION

The Arbitration Board for Medical Liability Issues of the Medical Association of North Germany ("Norddeutsche Schlichtungsstelle") is responsible for 10 federal states in Germany (Berlin, Brandenburg, Bremen, Hamburg, Mecklenburg-Western Pomerania, Lower Saxony, Saarland, Saxony-Anhalt, Schleswig-Holstein and Thuringia) and is the largest arbitration board in Germany. The data available from the Norddeutsche Schlichtungsstelle provides an insight into sources of malpractice during the treatment of reduction mammoplasty.

MATERIAL UND METHODS

We analysed patient request, expert opinions prepared by independent physicians on behalf of the Norddeutsche Schlichtungsstelle and the final verdicts of 88 arbitration proceedings after breast reduction mammoplasties performed between 2000 and 2007. This data allows for each case to be addressed from different viewpoints. Furthermore we analysed the statistical data entered into the Medical Error Reporting System by the arbitration board.

RESULTS

Among the 88 patient requests after reduction mammoplasty, the arbitration board found a causal relationship between damage caused to a patient's health and medical malpractice in 37 cases. Therefore, 42% of requests resulted in a liability case. This is a higher rate than that of general arbitration proceedings, where only in 24% of all cases a causal relationship is confirmed by the Norddeutsche Schlichtungsstelle. Most patients were operated on by gynaecologists. In 92% of liability cases, mistakes happened during the planning and the performance of the surgical procedure, mainly during planning (65%) and surgical incisions (41%). The patients mainly complained about scars (78%), asymmetry (68%) and skin necrosis of the areola (24%). Financial disadvantage was mentioned less often (46%) than psychological stress (70%).

DISCUSSION

The higher rate of liability claims may be due to the fact the surgical procedures changing the shape of breasts are more complex than generally expected. Not only the surgery itself, but also the adequate planning and aftercare are of predominant importance for patient satisfaction. All these factors lead to the relatively high rate of medical malpractice in plastic aesthetic breast surgery. Also the communication factor should not be underestimated.

[Viability and Particle Size of Fat Grafts Obtained with WAL and PAL Techniques]

BACKGROUND

Water jet-assisted liposuction (WAL) and power-assisted liposuction (PAL) are used for autologous fat grafting. This study analyses the viability and particle sizes of fat grafts obtained by these techniques.

PATIENTS, MATERIAL AND METHODS

The WAL and PAL techniques were applied in 9 female patients in identical body regions. In order to analyse cell viability, fat grafts were tested via the WST-8 assay and DNA quantification immediately after liposuction. Furthermore, in order to determine particle size, an optically evaluable water-fat emulsion was analysed by macroscopic inspection and light microscopy.

RESULTS

The WST-8 assay showed significantly lower extinction values (OD) for use of the WAL technique - corresponding to a lower metabolical activity - compared to PAL liposuction: WAL 1.85±0.56 OD, PAL 2.25±0.57 OD. The quotient of extinction values and cell DNA concentration determined by DNA quantification also indicated statistically significant differences between both systems of liposuction in favour of using power-assisted systems: WAL 0.061±0.023 OD/μg, PAL 0.083±0.029 OD/μg. On the other hand, microscopic and macroscopic analyses showed significantly greater diameters (d) for fat grafts obtained with the PAL technique than by WAL liposuction: dmakroWAL=0.8 mm and dmakroPAL=1.1 mm or, respectively, dmikroWAL 0.89 mm and dmikroPAL=0.93 mm.

CONCLUSION

Power-assisted liposuction obtains fat grafts with a higher metabolical activity than water jet-assisted liposuction. A falsification of extinction values within the WST-8 assay due to diversity of the number of cells was eliminated by additionally implemented DNA quantification. According to the current scientific debate, the particle size of obtained fat grafts is also considered as an important criterion for the success of autologous fat grafting. For clinical use, one should favour techniques which provide the smallest and most viable fat grafts as possible. In our opinion, the significantly lower size of WAL particles compared to the higher viability of PAL grafts indicates a necessity of analysing viability as well as particle size in order to evaluate liposuction systems. Data solely about in vitro viability of fat grafts fail to offer a recommendation for the use of a specific technique.

Identification of Candida glabrata genes involved in pH modulation and modification of the phagosomal environment in macrophages

Candida glabrata currently ranks as the second most frequent cause of invasive candidiasis. Our previous work has shown that C. glabrata is adapted to intracellular survival in macrophages and replicates within non-acidified late endosomal-stage phagosomes. In contrast, heat killed yeasts are found in acidified matured phagosomes. In the present study, we aimed at elucidating the processes leading to inhibition of phagosome acidification and maturation. We show that phagosomes containing viable C. glabrata cells do not fuse with pre-labeled lysosomes and possess low phagosomal hydrolase activity. Inhibition of acidification occurs independent of macrophage type (human/murine), differentiation (M1-/M2-type) or activation status (vitamin D₃ stimulation). We observed no differential activation of macrophage MAPK or NFκB signaling cascades downstream of pattern recognition receptors after internalization of viable compared to heat killed yeasts, but Syk activation decayed faster in macrophages containing viable yeasts. Thus, delivery of viable yeasts to non-matured phagosomes is likely not triggered by initial recognition events via MAPK or NFκB signaling, but Syk activation may be involved. Although V-ATPase is abundant in C. glabrata phagosomes, the influence of this proton pump on intracellular survival is low since blocking V-ATPase activity with bafilomycin A1 has no influence on fungal viability. Active pH modulation is one possible fungal strategy to change phagosome pH. In fact, C. glabrata is able to alkalinize its extracellular environment, when growing on amino acids as the sole carbon source in vitro. By screening a C. glabrata mutant library we identified genes important for environmental alkalinization that were further tested for their impact on phagosome pH. We found that the lack of fungal mannosyltransferases resulted in severely reduced alkalinization in vitro and in the delivery of C. glabrata to acidified phagosomes. Therefore, protein mannosylation may play a key role in alterations of phagosomal properties caused by C. glabrata.

[E-mail in plastic surgery--a useful addition to current communication possibilities?]

The internet is a global network of computers with a broad variety of services and options. It offers completely new ways of communication and investigation. At present, this new medium seems to be the final technical revolution in communication. It presents new dimensions which were utopia so far. Electronic mail (e-mail) is the most frequently used service within the internet. For a plastic surgeon it seems to be the fastest and the most cost-effective way of transferring data of any kind. The aim of this paper is to critically assess the transfer of confidential data via e-mail as well as to present general conditions for the use of e-mails. Therefore, our own experiences made with this technology are described to point to the possibilities, but also to indicate problems and weaknesses of this medium. Some rules should be obeyed for the transfer of confidential patient data via e-mail in order to satisfy the demand for data-security standards. Also medicolegal aspects must be considered. These recommendations or rules and aspects will be discussed to offer a guideline to plastic surgeons for their e-mail applications.

Communication in plastic surgery by means of e-mail: experiences and recommendations for clinical use

The Internet is a global network of computers with a broad variety of services and options. Electronic mail (email) is the most frequently used service. For a plastic surgeon, this mode is the fastest and the most cost-effective way of transferring data of any kind. The critical aim of this study was to assess the transfer of confidential data by means of e-mail and to present general conditions for the use of e-mail. Therefore, experiences with this means of communication are described to point to the possibilities, but also to indicate problems and weak points of this medium. Some rules should be obeyed for the transfer of confidential patient data by means of e-mail to satisfy the demand for data-security standards. Also, medicolegal aspects must be considered. These recommendations or rules and aspects will be discussed to offer a guideline to plastic surgeons for their e-mail applications.

[Comments on the topic of attesting to health status at arrest during medical emergency care]

A common problem for Emergency Room doctors on call is whether or not an arrested patient is sufficiently healthy to allow his transfer to jail. When there are signs of injury, or doubts about the patient's condition, the police must bring the patient in for medical examination to get a certification of the patient's health condition. He must be examined according to the information about his health and pre-existing conditions. Additional treatment should be undertaken, depending on patient's condition. The diagnoses must be written and summarized accurately and concisely. Additional documentation, such as photographic evidence must also be saved in the medical records. Should there be symptoms of a serious but difficult to diagnose condition, like traumatic head injury, the patient should always be admitted to the hospital. The medical certification or permission for imprisonment can not be enforced when the medical condition of the patient changes.

Purification and characterisation of the phosphoglycerate kinase isoenzymes of Trypanosoma brucei expressed in Escherichia coli

The Trypanosoma brucei phosphoglycerate kinase (PGK) glycosomal and cytosolic isoenzymes have been overexpressed in Escherichia coli and purified to near-homogeneity. Both enzymes were similar to the corresponding natural proteins with respect to their physicochemical and kinetic properties. In addition, a mutant of the glycosomal PGK lacking the 20 amino acid long C-terminal extension was overexpressed and purified. Various properties of this truncated glycosomal PGK were examined and it was found that in some aspects the protein behaved quite differently when compared with its natural counterpart. This was notably the case for the apparent Km for 3-phosphoglyceric acid, its sensitivity to inhibitors and its response to salts and guanidine HCl. However, its Vmax was found to be similar to that of the natural glycosomal PGK. These results suggest that the changes in the C-terminus caused a conformational change effecting the 3-phosphoglyceric acid binding site located at the N-terminal domain of the protein.

Molecular analysis of the cytosolic and glycosomal glyceraldehyde-3-phosphate dehydrogenase in Leishmania mexicana

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity was detected in two cell compartments of Leishmania mexicana promastigotes. These activities could be attributed to two different isoenzymes, one residing in glycosomes, the other in the cytosol. We have cloned and sequenced the genes for both isoenzymes. The glycosomal enzyme is encoded by two tandemly linked genes of identical sequence and contains features frequently found in glycosomal enzymes: the presence of peptide insertions, a small carboxy-terminal extension with a potential glycosomal targeting signal (-SKM) and an excess of positively charged residues (net charge +7). Only one open reading frame was detected for the cytosolic enzyme. The amino acid sequences of the two proteins are only 55% identical. We discuss some evolutionary aspects of the observed organization of the GAPDH genes in the Trypanosomatidae and the role of the two isoenzymes in the metabolism of these organisms. The possibility to develop GAPDH-specific inhibitors that will be effective against the enzyme of various parasitic members of this family is explored.

Molecular cloning and analysis of two tandemly linked genes for pyruvate kinase of Trypanosoma brucei

In Trypanosoma brucei (stock 427) genes encoding the glycolytic enzyme pyruvate kinase are present on two homologous chromosomes. We have cloned and characterized one of the alleles. Two large, tandemly arranged open reading frames were found, each coding for a pyruvate kinase polypeptide of 498 amino acids. The gene sequences differ at 15 positions, resulting in five amino acid substitutions. The calculated molecular masses of the polypeptides are 54,378 Da and 54,363 Da. These values are somewhat smaller than those reported for the subunit molecular mass of the purified protein, which is 57-59 kDa. However, in vitro translation of the DNA region corresponding to the open reading frame, and translation of the RNA in a wheat-germ lysate, yielded a product that comigrated exactly with the native polypeptide in SDS/PAGE. The overall identity between the sequences of the trypanosomal enzyme and the enzymes from other sources is 41-51%. The conserved residues are not equally distributed over the polypeptide. The primary structure of domains A and, to a lesser extent, B, which constitute the active site, are rather well conserved. In contrast, the sequence of domain C, which supposedly is involved in the regulation of the enzyme activity, is much more variable. The cytosolically located pyruvate kinase of T. brucei lacks the specific features found in the majority of the glycolytic enzymes of this organism that are sequestered in a microbody-like organelle, the glycosome. It has neither a relatively high subunit molecular mass, due to unique insertions or terminal extensions, nor a high excess of positively charged amino acids. The polypeptide is shorter than that of most other pyruvate kinases and the calculated net charge is only +3.

The cytosolic and glycosomal isoenzymes of glyceraldehyde-3-phosphate dehydrogenase in Trypanosoma brucei have a distant evolutionary relationship

Trypanosoma brucei contains two isoenzymes for glyceraldehyde-3-phosphate dehydrogenase: one enzyme resides in a microbody-like organelle, the glycosome; the other is found in the cytosol. Previously we have reported the characterization of the gene for the glycosomal enzyme [Michels, P. A. M., Poliszczak, A., Osinga, K. A., Misset, O., Van Beeumen, J., Wierenga, R. K., Borst, P. & Opperdoes, F. R. (1986) EMBO J. 5, 1049-1056]. Here we describe the cloning and analysis of the gene that codes for the cytosolic isoenzyme. The gene encodes a polypeptide of 330 amino acids, with a calculated molecular mass of 35440 Da. The two isoenzymes are only 55% identical. The cytosolic glyceraldehyde-3-phosphate dehydrogenase differs from the glycosomal enzyme in the following respects: (a) its subunit molecular mass is 3.4 kDa smaller due to the absence of insertions and a small C-terminal extension which are unique to the glycosomal protein; (b) the cytosolic enzyme has a lower pI (7.9, as compared to 9.3 for the glycosomal isoenzyme), which is due to a reduction in the excess of positively charged amino acids (the calculated net charges of the polypeptides are +2 and +11, respectively). We have compared the amino acid sequences of the two T. brucei glyceraldehyde-3-phosphate dehydrogenases, with 24 available sequences of the corresponding enzyme of other organisms from various phylogenetic groups. On the basis of this comparison an evolutionary tree was constructed. This analysis strongly supports the theory that T. brucei diverged early in evolution from the main eukaryotic branch of the phylogenetic tree. Further, two separate branches for the lineages leading to Trypanosoma are inferred from the amino acid sequences, suggesting that the genes for the two glyceraldehyde-3-phosphate dehydrogenases of the trypanosome are distantly related and must have been acquired independently by the trypanosomal ancestor. The branching determined with the glycosomal enzyme precedes that found with the cytosolic enzyme. The available data do not allow us to decide which of the two genes originally belonged to the trypanosome lineage and which entered the cell later by horizontal gene transfer.