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Aspergillus fumigatus arp1 modulates conidial pigmentation and complement deposition
H F Tsai1, R G Washburn, Y C Chang
1Laboratory of Clinical Investigation, National Institute of Allergy and Infectious Diseases, Bethesda, MD, USA.
Abstract:
Aspergillus fumigatus is an important pathogen causing invasive pulmonary aspergillosis in immunocompromised patients. The fungus propagates by conidia, which are the infectious structures inhaled by the human host. Opsonophagocytosis is thought to contribute to clearance of the inhaled conidia, a process that is facilitated by complement deposition on conidial surfaces. We now show that conidial colour mutants exhibit significant increases in C3 binding capacity compared with wild type. A reddish-pink mutation that led to enhanced C3 binding was complemented by a cosmid clone. A 3.3 kb DNA fragment from the subsequently rescued cosmid was sufficient to restore the bluish-green conidial pigment. The bluish-green transformant exhibited a level of C3 binding similar to that of the parental strain. A gene, designated arp1, was responsible for the complementation. Comparison of the genomic and cDNA sequences of arp1 revealed that it has two introns and encodes a putative protein of 168 amino acids. Arp1 is very similar to scytalone dehydratase, an enzyme involved in 1,8-dihydroxynaphthalene-melanin synthesis in Colletotrichum lagenarium and Magnaporthe grisea. Northern hybridization analysis revealed that arp1 is developmentally regulated, being expressed during conidiation. Disruption of arp1 resulted in reddish-pink conidia and increased C3 binding. Our studies suggest that arp1 modulates the bluish-green pigmentation of conidia as well as complement deposition.
Insights
The Aspergillus fumigatus arp1 gene controls conidial pigment and complement deposition. Disruption of arp1 leads to reddish-pink conidia with increased C3 binding, impacting opsonophagocytosis.
Area of Science:
- Mycology
- Immunology
- Molecular Biology
Background:
- Aspergillus fumigatus causes invasive pulmonary aspergillosis in immunocompromised individuals.
- Conidia are the infectious fungal structures inhaled by the host.
- Opsonophagocytosis, enhanced by complement deposition, aids conidial clearance.
Purpose of the Study:
- To investigate the role of conidial pigmentation in Aspergillus fumigatus immune evasion.
- To identify genes involved in regulating conidial color and complement binding.
Main Methods:
- Analysis of conidial color mutants and their C3 binding capacity.
- Complementation of a reddish-pink mutant using a cosmid clone.
- DNA sequencing and characterization of the identified gene, arp1.
- Northern hybridization to assess arp1 expression during conidiation.
- Gene disruption to confirm arp1 function.
Main Results:
- Conidial color mutants showed increased C3 binding compared to wild type.
- A 3.3 kb DNA fragment containing the arp1 gene restored bluish-green pigmentation and normal C3 binding.
- Arp1 encodes a putative 168-amino acid protein similar to scytalone dehydratase.
- Arp1 expression is developmentally regulated during conidiation.
- Disruption of arp1 resulted in reddish-pink conidia with elevated C3 binding.
Conclusions:
- The arp1 gene modulates Aspergillus fumigatus conidial pigmentation.
- Arp1 influences complement deposition on conidia.
- These findings suggest a link between fungal pigment and host immune response evasion.