Hemoglobin Uptake by Paracoccidioides spp. Is Receptor-Mediated

Abstract

Iron is essential for the proliferation of fungal pathogens during infection. The availability of iron is limited due to its association with host proteins. Fungal pathogens have evolved different mechanisms to acquire iron from host; however, little is known regarding how Paracoccidioides species incorporate and metabolize this ion. In this work, host iron sources that are used by Paracoccidioides spp. were investigated. Robust fungal growth in the presence of the iron-containing molecules hemin and hemoglobin was observed. Paracoccidioides spp. present hemolytic activity and have the ability to internalize a protoporphyrin ring. Using real-time PCR and nanoUPLC-MSE proteomic approaches, fungal growth in the presence of hemoglobin was shown to result in the positive regulation of transcripts that encode putative hemoglobin receptors, in addition to the induction of proteins that are required for amino acid metabolism and vacuolar protein degradation. In fact, one hemoglobin receptor ortholog, Rbt5, was identified as a surface GPI-anchored protein that recognized hemin, protoporphyrin and hemoglobin in vitro. Antisense RNA technology and Agrobacterium tumefaciens-mediated transformation were used to generate mitotically stable Pbrbt5 mutants. The knockdown strain had a lower survival inside macrophages and in mouse spleen when compared with the parental strain, which suggested that Rbt5 could act as a virulence factor. In summary, our data indicate that Paracoccidioides spp. can use hemoglobin as an iron source most likely through receptor-mediated pathways that might be relevant for pathogenic mechanisms.

Shu1 Is a Cell-surface Protein Involved in Iron Acquisition from Heme in Schizosaccharomyces pombe

“…Other yeasts such as Candida parapsilosis and Paracoccidioides brasiliensis use Rbt5-like proteins to acquire heme (18,19). In the case of Cryptococcus neoformans, the extracellular heme-binding glycoprotein Cig1 is required for exogenous heme uptake (20).…”

Paracoccidioides restrepiensis B339 (PS3) and P. lutzii LDR2 yeast cells and soluble components display in vitro hemolytic and hemagglutinating activities on human erythrocytes

“…Bailão et al . found the opposite was true for P. brasiliensis Pb18 (S1) and P. lutzii Pb01 and sheep erythrocytes . We believe that these contrasting results may be attributable to differences in our strains of P. lutzii (LDR2) and P. restrepiensis (B339); however, we cannot rule out a possible influence of iron in the culture medium because we did not use a completely iron‐free agar before CFA production.…”

“…This study demonstrated the presence of a hemolytic factor on the cell surface and as a secreted component for releasing hemoglobin, as hypothesized by Bailão et al . . The same group demonstrated that this is a possible iron source; they found that there was no upregulation of zrt1 transcript, which encodes for a zinc/iron permease, after incubation of yeasts of P. brasiliensis with human blood, suggesting there is no limit on available iron in this situation .…”

New insights into a complex fungal pathogen: the case of Paracoccidioides spp.

“…In another related study, it was also demonstrated that Paracoccidioides may use haemoglobin as an iron source, most probably through receptor‐mediated pathways, since iron‐related genes that encode haemoglobin receptors were identified in the genome of this fungal pathogen. In this study, the authors observed that expression of these related genes, including those encoding for proteins involved in amino acid assembly, as well as nitrogen, sulphur and iron–sulphur metabolism, were induced under low‐inorganic iron conditions or in the presence of haemoglobin (Bailão et al ., ).…”