RESUMO
Aspergillus fumigatus is a worldwide-distributed saprophytic fungus and the major cause of invasive aspergillosis. This fungus can produce two types of melanin-dihydroxynaphthalene melanin (DHN-melanin) and pyomelanin. These pigments are considered important resistance mechanisms to stress, as well as virulence factors. The aim of this review is to present the current knowledge of the genetic basis and metabolic pathways of melanin production, their activation, function, and interaction with the host immune system. The DHN-melanin pathway is encoded in a cluster that includes six genes (abr1, abr2, ayg1, arp1, arp2, and pksP/alb1 genes) whose encoded proteins seem to be the origin of the pigment in endosomes. These vesicles are secreted and the pigment is subsequently located in the wall of the conidium beneath the rodlet layer. Unlike DHN-melanin, pyomelanin does not have its own biosynthetic pathway but is related to the activation of the L-tyrosine/L-phenylalanine degradation pathway that includes a cluster of six genes (hppD, hmgX, hmgA, fahA, maiA, and hmgR). Its production is due to the polymerization of homogentisic acid and is linked to conidial germination. Despite the knowledge gained in recent years, further studies will be necessary to confirm the pathways that produce these pigments and their role in the virulence mechanisms of A. fumigatus.
Assuntos
Aspergilose/metabolismo , Aspergilose/microbiologia , Aspergillus fumigatus/fisiologia , Interações Hospedeiro-Patógeno , Melaninas/metabolismo , Aspergilose/genética , Aspergilose/imunologia , Regulação da Expressão Gênica , Interações Hospedeiro-Patógeno/genética , Interações Hospedeiro-Patógeno/imunologia , Sistema Imunitário/imunologia , Sistema Imunitário/metabolismo , Melaninas/genética , Redes e Vias Metabólicas , Ligação Proteica , VirulênciaRESUMO
It is generally accepted that the mineral core synthesized by ferritin-like proteins consists of a ferric oxy-hydroxide mineral similar to ferrihydrite in the case of horse spleen ferritin (HoSF) and an oxy-hydroxide-phosphate phase in plant and prokaryotic ferritins. The structure reflects a dynamic process of deposition and dissolution, influenced by different biological, chemical and physical variables. In this work we shed light on this matter by combining a structural (High Resolution Transmission Electron Microscopy (HRTEM) and Fe K-edge X-ray Absorption Spectroscopy (XAS)) and a magnetic study of the mineral core biomineralized by horse spleen ferritin (HoSF) and three prokaryotic ferritin-like proteins: bacterial ferritin (FtnA) and bacterioferritin (Bfr) from Escherichia coli and archaeal ferritin (PfFtn) from Pyrococcus furiosus. The prokaryotic ferritin-like proteins have been studied under native conditions and inside the cells for the sake of preserving their natural attributes. They share with HoSF a nanocrystalline structure rather than an amorphous one as has been frequently reported. However, the presence of phosphorus changes drastically the short-range order and magnetic response of the prokaryotic cores with respect to HoSF. The superparamagnetism observed in HoSF is absent in the prokaryotic proteins, which show a pure atomic-like paramagnetic behaviour attributed to phosphorus breaking the Fe-Fe exchange interaction.
Assuntos
Ferritinas/química , Magnetismo , Nanotecnologia/métodos , Animais , Proteínas de Bactérias/química , Grupo dos Citocromos b/química , Eletroforese em Gel de Poliacrilamida , Escherichia coli/química , Cavalos , Hidróxidos/química , Ferro/química , Microscopia Eletrônica de Transmissão , Nanopartículas , Fósforo/química , Pyrococcus furiosus/química , Proteínas Recombinantes/química , Espectrofotometria , Baço/químicaRESUMO
Invasive aspergillosis is an opportunistic infection caused primarily by Aspergillus fumigatus. However, other common fungal pathogens belonging to section Fumigati are often misidentified as A. fumigatus. Thus, we have developed a multiplex real-time PCR (qPCR) assay with primers and specific TaqMan probes based on internal transcribed spacer regions or benA gene to discriminate, in less than 3 h, species of section Fumigati and, specifically, A. fumigatus. The multiplex qPCR showed a limit of detection of 20 and 50 fg of DNA for section Fumigati and A. fumigatus, respectively. Moreover, it enabled detection of a single germinated conidia. The inclusion of some PCR facilitators together with the dilution of samples makes it possible to completely avoid PCR inhibitions in all bronchoalveolar lavage (BAL) samples assayed. This technique may be a useful complementary tool in the diagnosis of invasive pulmonary aspergillosis caused by A. fumigatus using BAL fluid.
