RESUMEN
In the Saccharomyces cerevisiae glycolytic pathway, 11 enzymes catalyze the stepwise conversion of glucose to two molecules of ethanol plus two CO2 molecules. In the highly crowded cytoplasm, this pathway would be very inefficient if it were dependent on substrate/enzyme diffusion. Therefore, the existence of a multi-enzymatic glycolytic complex has been suggested. This complex probably uses the cytoskeleton to stabilize the interaction of the various enzymes. Here, the role of filamentous actin (F-actin) in stabilization of a putative glycolytic metabolon is reported. Experiments were performed in isolated enzyme/actin mixtures, cytoplasmic extracts and permeabilized yeast cells. Polymerization of actin was promoted using phalloidin or inhibited using cytochalasin D or latrunculin. The polymeric filamentous F-actin, but not the monomeric globular G-actin, stabilized both the interaction of isolated glycolytic pathway enzyme mixtures and the whole fermentation pathway, leading to higher fermentation activity. The associated complexes were resistant against inhibition as a result of viscosity (promoted by the disaccharide trehalose) or inactivation (using specific enzyme antibodies). In S. cerevisiae, a glycolytic metabolon appear to assemble in association with F-actin. In this complex, fermentation activity is enhanced and enzymes are partially protected against inhibition by trehalose or by antibodies.
Asunto(s)
Citoesqueleto de Actina/metabolismo , Actinas/metabolismo , Glucólisis , Metaboloma , Complejos Multienzimáticos/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Citoesqueleto de Actina/efectos de los fármacos , Actinas/agonistas , Actinas/antagonistas & inhibidores , Actinas/química , Anticuerpos Antifúngicos/farmacología , Compuestos Bicíclicos Heterocíclicos con Puentes/farmacología , Citocalasina D/farmacología , Citoplasma/efectos de los fármacos , Citoplasma/enzimología , Citoplasma/metabolismo , Estabilidad de Enzimas/efectos de los fármacos , Fermentación/efectos de los fármacos , Glucólisis/efectos de los fármacos , Cinética , Metaboloma/efectos de los fármacos , Complejos Multienzimáticos/antagonistas & inhibidores , Complejos Multienzimáticos/química , Faloidina/farmacología , Polimerizacion/efectos de los fármacos , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/enzimología , Proteínas de Saccharomyces cerevisiae/agonistas , Proteínas de Saccharomyces cerevisiae/antagonistas & inhibidores , Proteínas de Saccharomyces cerevisiae/química , Tiazolidinas/farmacología , Trehalosa/farmacología , Moduladores de Tubulina/farmacología , ViscosidadRESUMEN
BACKGROUND: Studies carried out during the 1990's demonstrated the presence of fungal glycoinositol phosphorylceramides (GIPCs) with unique structures, some of them showed reactivity with sera of patients with histoplasmosis, paracoccidioidomycosis or aspergillosis. It was also observed that fungal GIPCs were able to inhibit T lymphocyte proliferation "in vitro", and studies regarding the importance of these molecules to fungal survival showed that many species of fungi are vulnerable to inhibitors of sphingolipid biosynthesis. RESULTS: In this paper, we describe a detailed characterization of an IgG2a monoclonal antibody (mAb), termed MEST-3, directed to the Paracoccidioides brasiliensis glycolipid antigen Pb-2 (Manpalpha1-->3Manpalpha1-->2IPC). mAb MEST-3 also recognizes GIPCs bearing the same structure in other fungi. Studies performed on fungal cultures clearly showed the strong inhibitory activity of MEST-3 on differentiation and colony formation of Paracoccidioides brasiliensis, Histoplasma capsulatum and Sporothrix schenckii. Similar inhibitory results were observed when these fungi where incubated with a different mAb, which recognizes GIPCs bearing terminal residues of beta-D-galactofuranose linked to mannose (mAb MEST-1). On the other hand, mAb MEST-2 specifically directed to fungal glucosylceramide (GlcCer) was able to promote only a weak inhibition on fungal differentiation and colony formation. CONCLUSIONS: These results strongly suggest that mAbs directed to specific glycosphingolipids are able to interfere on fungal growth and differentiation. Thus, studies on surface distribution of GIPCs in yeast and mycelium forms of fungi may yield valuable information regarding the relevance of glycosphingolipids in processes of fungal growth, morphological transition and infectivity.
Asunto(s)
Anticuerpos Antifúngicos/farmacología , Anticuerpos Monoclonales/farmacología , Hongos/efectos de los fármacos , Glicoesfingolípidos/inmunología , Anticuerpos Antifúngicos/química , Anticuerpos Antifúngicos/metabolismo , Anticuerpos Monoclonales/química , Anticuerpos Monoclonales/metabolismo , Antígenos Fúngicos/inmunología , Proliferación Celular/efectos de los fármacos , Técnica del Anticuerpo Fluorescente Indirecta , Hongos/citología , Hongos/fisiología , Glicoesfingolípidos/metabolismo , Histoplasma/citología , Histoplasma/efectos de los fármacos , Histoplasma/fisiología , Inmunoglobulina G/química , Inmunoglobulina G/metabolismo , Inmunoglobulina G/farmacología , Fenómenos Microbiológicos/efectos de los fármacos , Micelio/citología , Micelio/efectos de los fármacos , Micelio/crecimiento & desarrollo , Paracoccidioides/citología , Paracoccidioides/efectos de los fármacos , Paracoccidioides/fisiología , Sporothrix/citología , Sporothrix/efectos de los fármacos , Sporothrix/fisiologíaRESUMEN
Fungal glucosylceramides (GlcCer) are conserved lipid components in a large variety of pathogenic and non-pathogenic fungal species, but their biological functions are still unclear. Recent studies demonstrate that GlcCer are immunologically active components inducing the production of antifungal antibodies. In this work, a major GlcCer was purified and characterized from mycelial forms of Fonsecaea pedrosoi, the most frequent causative agent of chromoblastomycosis. As determined by fast atom bombardment mass spectrometry (FAB-MS) analysis, the purified molecule was identified as the conserved structure N-2'-hydroxyhexadecanoyl-1-beta-D-glucopyranosyl-9-methyl-4,8-sphingadienine. A monoclonal antibody (Mab) against this structure was used in indirect immunofluorescence with the different morphological stages of F. pedrosoi. Only the surface of young dividing cells was recognized by the antibody. Treatment of F. pedrosoi conidia with the Mab against GlcCer resulted in a clear reduction in fungal growth. In addition, the Mab also enhanced phagocytosis and killing of F. pedrosoi by murine cells. These results suggest that, in F. pedrosoi, GlcCer seem to be cell wall components targeted by antifungal antibodies that directly inhibit fungal development and also enhance macrophage function, supporting the use of monoclonal antibodies to GlcCer as potential tools in antifungal immunotherapy.
Asunto(s)
Anticuerpos Antifúngicos/farmacología , Anticuerpos Monoclonales/farmacología , Ascomicetos/efectos de los fármacos , Ascomicetos/crecimiento & desarrollo , Glucosilceramidas/inmunología , Fagocitosis/efectos de los fármacos , Animales , Anticuerpos Antifúngicos/inmunología , Anticuerpos Monoclonales/inmunología , Ascomicetos/química , Ascomicetos/inmunología , Cromoblastomicosis/inmunología , Cromoblastomicosis/microbiología , Femenino , Glucosilceramidas/química , Humanos , Macrófagos Peritoneales/efectos de los fármacos , Macrófagos Peritoneales/inmunología , Macrófagos Peritoneales/microbiología , RatonesRESUMEN
The surface glycoprotein gp43, a highly immunogenic component of Paracoccidioides brasiliensis, is used in the serodiagnosis of paracoccidioidomycosis (PCM) and has recently been shown to specifically bind the extracellular matrix protein laminin. Binding to laminin induces the increased adhesion of the fungus to epithelial cells; a hamster testicle infection model has shown that the gp43-dependent binding of fungal cells to laminin enhances their pathogenicity in vivo. We report on the production and characterization of 12 monoclonal antibodies against the gp43 that recognize peptide sequences in the molecule detecting at least three different epitopes as well as different isoforms of this antigen. MAbs interfered in the fungal pathogenicity in vivo either by inhibiting or enhancing granuloma formation and tissue destruction. Results suggest that P. brasiliensis propagules may start infection in man by strongly adhering to human lung cells. Thus, laminin-mediated fungal adhesion to human lung carcinoma (A549) cells was much more intense than to Madin-Darby canine kidney cells (MDCK), indicating differences in binding affinity. Subsequent growth of fungi bound to the lung cells could induce the granulomatous inflammatory reaction characteristic of PCM. Both steps are greatly stimulated by laminin binding in infective cells expressing gp43.