The putative α-1,2-mannosyltransferase AfMnt1 of the opportunistic fungal pathogen Aspergillus fumigatus is required for cell wall stability and full virulence
Author:
Wagener J, Echtenacher B, Rohde M, Kotz A, Krappmann S, Heesemann J, Ebel F
Date: 30 September 2008
Abstract:
Proteins entering the eukaryotic secretory pathway are commonly glycosylated. Important steps in this post translational modification are carried out by mannosyltransferases. In this study, we investigated the putative α-1,2-mannosyltransferase AfMnt1 of the human pathogenic mould Aspergillus fumigatus. AfMnt1 belongs to a family of enzymes that comprises nine members in Saccharomyces cerevisiae, but only three in A. fumigatus. A δafmnt1 mutant is viable and grows normally at 37 degrees C, but its hyphal cell wall appears to be thinner than that of the parental strain. Lack of AfMnt1 leads to a higher sensitivity to calcofluor white and Congo red, but not to SDS. Growth of the mutant is abrogated at 48 degrees C, but can be restored by osmotic stabilization. The resulting colonies remain white, due to a defect in the formation of conidia. Electron- and immunofluorescence microscopy furthermore revealed that the observed growth defect of the mutant at 48 degrees C can be attributed to cell wall instability resulting in leakage at the hyphal tips. Using an RFP fusion protein we localized AfMnt1 in compact, BrefeldinA-sensitive organelles that most likely represent fungal Golgi equivalents. The TNFalpha response of murine macrophages to hyphae was not affected by the lack of the afmnt1 gene, but the corresponding mutant was attenuated in a mouse model of infection. This and the increased sensitivity of the δafmnt1 mutant to azoles, antifungal agents that are currently used to treat Aspergillus infections, suggest that α-1,2-mannosyltransferases could be interesting targets for novel anti-fungal drugs.
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