Abstract
The ability to resist copper toxicity is important for microbial pathogens to survive attack by innate immune cells. A sur7Δ mutant of the fungal pathogen Candida albicans exhibits decreased virulence that correlates with increased sensitivity to copper, as well as defects in other stress responses and morphogenesis. Previous studies indicated that copper kills sur7Δ cells by a mechanism distinct from the known resistance pathways involving the Crp1 copper exporter or the Cup1 metallothionein. Since Sur7 resides in punctate plasma membrane domains known as MCC/eisosomes, we examined overexpression of SUR7 and found that it rescued the copper sensitivity of a mutant that fails to form MCC/eisosomes (pil1Δ lsp1Δ), indicating that these domains act to facilitate Sur7 function. Genetic screening identified new copper-sensitive mutants, the strongest of which were similar to sur7Δ in having altered plasma membranes due to defects in membrane trafficking, cortical actin, and morphogenesis (rvs161Δ, rvs167Δ, and arp2Δ arp3Δ). Consistent with the mutants having altered plasma membrane organization, they were all more readily permeabilized by copper, which is known to bind phosphatidylserine and phosphatidylethanolamine and cause membrane damage. Although these phospholipids are normally localized to the intracellular leaflet of the plasma membrane, their exposure on the surface of the copper-sensitive mutants was indicated by increased susceptibility to membrane damaging agents that bind to these phospholipids. Increased copper sensitivity was also detected for a drs2Δ mutant, which lacks a phospholipid flippase that is involved in maintaining phospholipid asymmetry. Copper binds phosphatidylserine with very high affinity, and deleting CHO1 to prevent phosphatidylserine synthesis rescued the copper sensitivity of sur7Δ cells, confirming a major role for phosphatidylserine in copper sensitivity. These results highlight how proper plasma membrane architecture protects fungal pathogens from copper and attack by the immune system, thereby opening up new avenues for therapeutic intervention.
Highlights
The human fungal pathogen C. albicans typically grows as a commensal organism on human mucosa
The transition metal copper is used by the innate immune system to attack microbial pathogens
To better understand how the human fungal pathogen Candida albicans resists this type of stress, we screened for mutants that were more susceptible to killing by copper
Summary
The human fungal pathogen C. albicans typically grows as a commensal organism on human mucosa. Serious infections occur when conditions promote an overgrowth of C. albicans that overwhelms the immune system. This can happen as a consequence of the use of antibacterial antibiotics that disrupt the microbiota or as the result of biofilm formation on medical devices and catheters. In order to survive in a human host, C. albicans must be able to resist a wide range of stressful conditions promoted by the immune system. This includes elevated temperature, antimicrobial peptides, oxidation, and nitrosylation [3,4,5]. Copper can react with H2O2 produced by the oxidative burst in phagosomes to form a broader array of damaging reactive oxygen species [6, 12, 13]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have