Candida albicans Scavenges Host Zinc via Pra1 during Endothelial Invasion

Abstract

The ability of pathogenic microorganisms to assimilate essential nutrients from their hosts is critical for pathogenesis. Here we report endothelial zinc sequestration by the major human fungal pathogen, Candida albicans . We hypothesised that, analogous to siderophore-mediated iron acquisition, C. albicans utilises an extracellular zinc scavenger for acquiring this essential metal. We postulated that such a “zincophore” system would consist of a secreted factor with zinc-binding properties, which can specifically reassociate with the fungal cell surface. In silico analysis of the C. albicans secretome for proteins with zinc binding motifs identified the p H- r egulated a ntigen 1 (Pra1). Three-dimensional modelling of Pra1 indicated the presence of at least two zinc coordination sites. Indeed, recombinantly expressed Pra1 exhibited zinc binding properties in vitro . Deletion of PRA1 in C. albicans prevented fungal sequestration and utilisation of host zinc, and specifically blocked host cell damage in the absence of exogenous zinc. Phylogenetic analysis revealed that PRA1 arose in an ancient fungal lineage and developed synteny with ZRT1 (encoding a zinc transporter) before divergence of the Ascomycota and Basidiomycota. Structural modelling indicated physical interaction between Pra1 and Zrt1 and we confirmed this experimentally by demonstrating that Zrt1 was essential for binding of soluble Pra1 to the cell surface of C. albicans . Therefore, we have identified a novel metal acquisition system consisting of a secreted zinc scavenger (“zincophore”), which reassociates with the fungal cell. Furthermore, functional similarities with phylogenetically unrelated prokaryotic systems indicate that syntenic zinc acquisition loci have been independently selected during evolution.

Broadly Conserved Fungal Effector BEC1019 Suppresses Host Cell Death and Enhances Pathogen Virulence in Powdery Mildew of Barley (Hordeum vulgare L.) (Retracted)

“…The two histidines in this motif represent two of three zinc-binding residues; the third residue is typically glutamic acid or aspartic acid (Vallee and Auld 1990). Though neither of the BEC1019 homologs Asp F2 and Pra1 has been shown to have protease activity when tested with casein as a substrate (Amich et al 2010;Citiulo et al 2012), Asp F2 plays a role in zinc acquisition (Amich et al 2010) and Pra1 can Fig. 6.…”

“…directly bind zinc (Citiulo et al 2012). Three-dimensional modeling predicts that Pra1 interacts with the zinc transporter Zrt1, a protein also shown to be important for Candida albicans virulence (Citiulo et al 2012).…”

“…Three-dimensional modeling predicts that Pra1 interacts with the zinc transporter Zrt1, a protein also shown to be important for Candida albicans virulence (Citiulo et al 2012). The Pra1 and Zrt1 genes are physically linked in the Candida albicans genome and are transcriptionally coregulated, as they share a common promoter (Citiulo et al 2012;Nobile et al 2009). The B. graminis genome encodes two Zrt1 homologs.…”

“…Several Fusarium species are also observed, including causal agents of Fusarium head blight of barley and wheat (F. graminearum), and sudden death syndrome (F. virguliforme) of soybean. Among the BEC1019 homologs from animal pathogens and free-living fungi are the characterized proteins Pra1 from Candida albicans (Citiulo et al 2012), major allergen Asp F2 from Aspergillus fumigatus (Amich et al 2010), and Zps1 (Lamb et al 2001) from Saccharomyces cerevisiae. As of January 23, 2014, no hits were obtained from tBLASTn searches of BEC1019 in the sequences of the basidiomycete obligate biotrophs Puccinia graminis, P. striiformis, and P. recondita, however, a homolog was found in the basidiomycete corn smut pathogen, Ustilago maydis.…”

Iron restriction-induced adaptations in the wall proteome of Candida albicans

“…They function like a relay system, where some proteins are secreted to scavenge haem from associated host-proteins, while other family members are located in the thick wall at varying depths to further transport the acquired haem towards transporters across the membrane (Mazmanian et al, 2003). It is tempting to speculate that the C. albicans Rbt5 family members could collaborate in a similar way, with Csa2 being secreted as a haem-scavenging protein, similarly to the role of Pra1 in zinc sequestration (Citiulo et al, 2012), and Csa1, Pga7, Pga10 and Rbt5 being positioned at different places in the wall and the cell membrane to facilitate iron uptake. This could explain why five members of a protein family are induced under the same conditions.…”