Regulation of Nonribosomal Peptide Synthesis: bis-Thiomethylation Attenuates Gliotoxin Biosynthesis in Aspergillus fumigatus

Gliotoxin is a redox-active nonribosomal peptide produced by Aspergillus fumigatus. Like many other disulfide-containing epipolythiodioxopiperazines, a bis-thiomethylated form is also produced. In the case of gliotoxin, bisdethiobis(methylthio)gliotoxin (BmGT) is formed for unknown reasons by a cryptic enzyme. Here, we identify the S-adenosylmethionine- dependent gliotoxin bis-thiomethyltransferase (GtmA), which converts dithiogliotoxin to BmGT. This activity, which is induced by exogenous gliotoxin, is only detectable in protein lysates of A. fumigatus deficient in the gliotoxin oxidoreductase, gliT. Thus, GtmA is capable of substrate bis-thiomethylation. Deletion of gtmA completely abrogates BmGT formation and we now propose that the purpose of BmGT formation is primarily to attenuate gliotoxin biosynthesis. Phylogenetic analysis reveals 124 GtmA homologs within the Ascomycota phylum. GtmA is encoded outside the gliotoxin biosynthetic cluster and primarily serves to negatively regulate gliotoxin biosynthesis. This mechanism of postbiosynthetic regulation of nonribosomal peptide synthesis appears to be quite unusual

The Aspergillus fumigatus Protein GliK Protects against Oxidative Stress and Is Essential for Gliotoxin Biosynthesis

The function of a number of genes in the gliotoxin biosynthetic cluster (gli) in Aspergillus fumigatus remains unknown. Here, we demonstrate that gliK deletion from two strains of A. fumigatus completely abolished gliotoxin biosynthesis. Furthermore, exogenous H2O2 (1 mM), but not gliotoxin, significantly induced A. fumigatus gliK expression (P 0.0101). While both mutants exhibited significant sensitivity to both exogenous gliotoxin (P<0.001) and H2O2 (P<0.01), unexpectedly, exogenous gliotoxin relieved H2O2-induced growth inhibition in a dose-dependent manner (0 to 10 g/ml). Gliotoxin-containing organic extracts derived from A. fumigatus ATCC 26933 significantly inhibited (P<0.05) the growth of the gliK26933 deletion mutant. The A. fumigatus gliK26933 mutant secreted metabolites, devoid of disulfide linkages or free thiols, that were detectable by reverse- phase high-performance liquid chromatography and liquid chromatography-mass spectrometry with m/z 394 to 396. These metabolites (m/z 394 to 396) were present at significantly higher levels in the culture supernatants of the A. fumigatus gliK26933 mutant than in those of the wild type (P0.0024 [fold difference, 24] and P0.0003 [fold difference, 9.6], respectively) and were absent from A. fumigatus gliG. Significantly elevated levels of ergothioneine were present in aqueous mycelial extracts of the A. fumigatus gliK26933 mutant compared to the wild type (P<0.001). Determination of the gliotoxin uptake rate revealed a significant difference (P0.0045) between that of A. fumigatus ATCC 46645 (9.3 pg/mg mycelium/min) and the gliK46645 mutant (31.4 pg/mg mycelium/min), strongly suggesting that gliK absence and the presence of elevated ergothioneine levels impede exogenously added gliotoxin efflux. Our results confirm a role for gliK in gliotoxin biosynthesis and reveal new insights into gliotoxin functionality in A. fumigatus

A liver fibrosis cocktail? Psoriasis, methotrexate and genetic hemochromatosis

BACKGROUND: Pathologists are often faced with the dilemma of whether to recommend continuation of methotrexate therapy for psoriasis within the context of an existing pro-fibrogenic risk factor, in this instance, patients with genetic hemochromatosis. CASE PRESENTATIONS: We describe our experience with two male psoriatic patients (A and B) on long term methotrexate therapy (cumulative dose A = 1.56 gms and B = 7.88 gms) with hetero- (A) and homozygous (B) genetic hemochromatosis. These patients liver function were monitored with routine biochemical profiling; apart from mild perivenular fibrosis in one patient (B), significant liver fibrosis was not identified in either patient with multiple interval percutaneous liver biopsies; in the latter instance this patient (B) had an additional risk factor of partiality to alcohol. CONCLUSION: We conclude that methotrexate therapy is relatively safe in patients with genetic hemochromatosis, with no other risk factor, but caution that the risk of fibrosis be monitored, preferably by non-invasive techniques, or by liver biopsy

Combination of contrast with stress echocardiography: A practical guide to methods and interpretation

Contrast echocardiography has an established role for enhancement of the right heart Doppler signals, the detection of intra-cardiac shunts, and most recently for left ventricular cavity opacification (LVO). The use of intravenously administered micro-bubbles to traverse the myocardial microcirculation in order to outline myocardial viability and perfusion has been the source of research studies for a number of years. Despite the enthusiasm of investigators, myocardial contrast echocardiography (MCE) has not attained routine clinical use and LV opacification during stress has been less widely adopted than the data would support. The purpose of this review is to facilitate an understanding of the involved imaging technologies that have made this technique more feasible for clinical practice, and to guide its introduction into the practice of the non-expert user

Mutation of the Zebrafish Nucleoporin elys Sensitizes Tissue Progenitors to Replication Stress

The recessive lethal mutation flotte lotte (flo) disrupts development of the zebrafish digestive system and other tissues. We show that flo encodes the ortholog of Mel-28/Elys, a highly conserved gene that has been shown to be required for nuclear integrity in worms and nuclear pore complex (NPC) assembly in amphibian and mammalian cells. Maternal elys expression sustains zebrafish flo mutants to larval stages when cells in proliferative tissues that lack nuclear pores undergo cell cycle arrest and apoptosis. p53 mutation rescues apoptosis in the flo retina and optic tectum, but not in the intestine, where the checkpoint kinase Chk2 is activated. Chk2 inhibition and replication stress induced by DNA synthesis inhibitors were lethal to flo larvae. By contrast, flo mutants were not sensitized to agents that cause DNA double strand breaks, thus showing that loss of Elys disrupts responses to selected replication inhibitors. Elys binds Mcm2-7 complexes derived from Xenopus egg extracts. Mutation of elys reduced chromatin binding of Mcm2, but not binding of Mcm3 or Mcm4 in the flo intestine. These in vivo data indicate a role for Elys in Mcm2-chromatin interactions. Furthermore, they support a recently proposed model in which replication origins licensed by excess Mcm2-7 are required for the survival of human cells exposed to replication stress

Resistance is not futile: gliotoxin biosynthesis, functionality and utility

Gliotoxin biosynthesis is encoded by the gli gene cluster in Aspergillus fumigatus. The biosynthesis of gliotoxin is influenced by a suite of transcriptionally-active regulatory proteins and a bis-thiomethyltransferase. A self-protection system against gliotoxin is present in A. fumigatus. Several additional metabolites are also produced via the gliotoxin biosynthetic pathway. Moreover, the biosynthesis of unrelated natural products appears to be influenced either by gliotoxin or by the activity of specific reactions within the biosynthetic pathway. The activity of gliotoxin against animal cells and fungi, often mediated by interference with redox homeostasis or protein modification, is revealing new metabolic interactions within eukaryotic systems. Nature has provided a most useful natural product with which to reveal some of its many molecular secret

Little by little

Gift of Dr. Mary Jane Esplen.Piano vocal ukulele [instrumentation]Seven days a week fifty two weeks a year [first line]Little By Little, Little By Little, You're winning [first line of chorus]F major [key]Moderato [tempo]Popular song [form/genre]Sally O'Neil and Eddie Quillan (photograph) [illustration]J. G. Keenan Barrie, Ont. Everything In Music [dealer stamp]Publisher's advertisement on back cover [note

The Aspergillus fumigatus Protein GliK Protects against Oxidative Stress and Is Essential for Gliotoxin Biosynthesis

The function of a number of genes in the gliotoxin biosynthetic cluster (gli) in Aspergillus fumigatus remains unknown. Here, we demonstrate that gliK deletion from two strains of A. fumigatus completely abolished gliotoxin biosynthesis. Furthermore, exogenous H2O2 (1 mM), but not gliotoxin, significantly induced A. fumigatus gliK expression (P 0.0101). While both mutants exhibited significant sensitivity to both exogenous gliotoxin (P<0.001) and H2O2 (P<0.01), unexpectedly, exogenous gliotoxin relieved H2O2-induced growth inhibition in a dose-dependent manner (0 to 10 g/ml). Gliotoxin-containing organic extracts derived from A. fumigatus ATCC 26933 significantly inhibited (P<0.05) the growth of the gliK26933 deletion mutant. The A. fumigatus gliK26933 mutant secreted metabolites, devoid of disulfide linkages or free thiols, that were detectable by reverse- phase high-performance liquid chromatography and liquid chromatography-mass spectrometry with m/z 394 to 396. These metabolites (m/z 394 to 396) were present at significantly higher levels in the culture supernatants of the A. fumigatus gliK26933 mutant than in those of the wild type (P0.0024 [fold difference, 24] and P0.0003 [fold difference, 9.6], respectively) and were absent from A. fumigatus gliG. Significantly elevated levels of ergothioneine were present in aqueous mycelial extracts of the A. fumigatus gliK26933 mutant compared to the wild type (P<0.001). Determination of the gliotoxin uptake rate revealed a significant difference (P0.0045) between that of A. fumigatus ATCC 46645 (9.3 pg/mg mycelium/min) and the gliK46645 mutant (31.4 pg/mg mycelium/min), strongly suggesting that gliK absence and the presence of elevated ergothioneine levels impede exogenously added gliotoxin efflux. Our results confirm a role for gliK in gliotoxin biosynthesis and reveal new insights into gliotoxin functionality in A. fumigatus

The Aspergillus fumigatus Protein GliK Protects against Oxidative Stress and Is Essential for Gliotoxin Biosynthesis

The function of a number of genes in the gliotoxin biosynthetic cluster (gli) in Aspergillus fumigatus remains unknown. Here, we demonstrate that gliK deletion from two strains of A. fumigatus completely abolished gliotoxin biosynthesis. Furthermore, exogenous H2O2 (1 mM), but not gliotoxin, significantly induced A. fumigatus gliK expression (P 0.0101). While both mutants exhibited significant sensitivity to both exogenous gliotoxin (P<0.001) and H2O2 (P<0.01), unexpectedly, exogenous gliotoxin relieved H2O2-induced growth inhibition in a dose-dependent manner (0 to 10 g/ml). Gliotoxin-containing organic extracts derived from A. fumigatus ATCC 26933 significantly inhibited (P<0.05) the growth of the gliK26933 deletion mutant. The A. fumigatus gliK26933 mutant secreted metabolites, devoid of disulfide linkages or free thiols, that were detectable by reverse- phase high-performance liquid chromatography and liquid chromatography-mass spectrometry with m/z 394 to 396. These metabolites (m/z 394 to 396) were present at significantly higher levels in the culture supernatants of the A. fumigatus gliK26933 mutant than in those of the wild type (P0.0024 [fold difference, 24] and P0.0003 [fold difference, 9.6], respectively) and were absent from A. fumigatus gliG. Significantly elevated levels of ergothioneine were present in aqueous mycelial extracts of the A. fumigatus gliK26933 mutant compared to the wild type (P<0.001). Determination of the gliotoxin uptake rate revealed a significant difference (P0.0045) between that of A. fumigatus ATCC 46645 (9.3 pg/mg mycelium/min) and the gliK46645 mutant (31.4 pg/mg mycelium/min), strongly suggesting that gliK absence and the presence of elevated ergothioneine levels impede exogenously added gliotoxin efflux. Our results confirm a role for gliK in gliotoxin biosynthesis and reveal new insights into gliotoxin functionality in A. fumigatus