Identification and characterization of an RXLR-like effector family from medically relevant fungi

Shiv D. Kale, Kelly C. Drews, Helen R. Clark, Hua Wise, Vincenzo Antignani, Tristan A. Hayes, Christopher B. Lawrence, Brett M. Tyler

Author address: 

Virginia Bioinformatics Institute, Virginia Tech., Blacksburg, VA


Fungal infections have become an increasingly significant problem for immunocompromised individuals, transplant recipients, the elderly, several cases involving healthy individuals. There is a significant growth in incidences of morbidity and mortality associated with medically important fungi, specifically Aspergillus species. Aspergillus fumigatus virulence has been attributed to production of pigments, adhesins on the surface of the cell wall, secreted proteases, and mycotoxins. Current treatments consist of oral corticosteroids, antifungal medications, and/or surgery to remove aspergillomas. Many of these treatments have substantial shortcomings. Detection and diagnosis is also weighty problem as most clinical tests take weeks for results allowing the infection to proceed. Appropriately, the paradigm for human fungal interactions has been focused on the host deficiencies mediating virulence of opportunistic pathogenic fungi. There has been substantial progress in identifying and characterizing secreted proteins (effectors) from bacterial, oomycete, and fungal plant pathogens. A subset of these effector proteins are able to enter host cells and modulate host intracellular functions. Using our bioinformatics pipeline we have been able to identify a family of secreted proteins from A. fumigatus sharing a conserved N-terminal RXLR-like motif. We found this family is expanded amongst primary fungal pathogens. The RXLR and RXLR-like motifs from known intracellular effectors of plant pathogenic and mutualistic oomycetes and fungi have been shown to facilitate effector entry into plant cells via binding external phosphatidylinositol-3-phosphate (PI3P). Here we describe AF2, a candidate effector from A. fumigatus that contains a N-terminal RxLR-like motif. Through the use of confocal microscopy and flow cytometry we show AF2 is rapidly able to enter several primary and immortalized mammalian cell lines. Through the use of isothermal titration calorimetry and liposome binding assays we show AF2 has nanomolar binding affinity for PI3P, and does not bind other mono or poly-PIPs that we have tested thus far. Based on our bioinformatics and biochemical analysis we postulate AF2 is a secreted effector protein capable of rapidly translocating into mammalian cells. We will present our latest findings on the physiological relevance of AF2

abstract No: 


Full conference title: 

27th Fungal Genetics Conference
    • FGC 27th (2013)