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Eukaryotic Cell, October 2008, p. 1661-1673, Vol. 7, No. 10
1535-9778/08/$08.00+0     doi:10.1128/EC.00221-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Putative -1,2-Mannosyltransferase AfMnt1 of the Opportunistic Fungal Pathogen Aspergillus fumigatus Is Required for Cell Wall Stability and Full Virulence

Max-von-Pettenkofer-Institut, Ludwig-Maximilians-Universität, Munich, Germany,¹ Institut für Immunologie, Universität Regensburg, Regensburg, Germany,² Helmholtz Zentrum für Infektionsforschung, Mikrobielle Pathogenität, Braunschweig, Germany,³ Zentrum für Infektionsforschung, Julius-Maximilians-Universität, Würzburg, Germany⁴

Received 7 July 2008/ Accepted 6 August 2008

Proteins entering the eukaryotic secretory pathway commonly are glycosylated. Important steps in this posttranslational modification are carried out by mannosyltransferases. In this study, we investigated the putative -1,2-mannosyltransferase AfMnt1 of the human pathogenic mold Aspergillus fumigatus. AfMnt1 belongs to a family of enzymes that comprises nine members in Saccharomyces cerevisiae but only three in A. fumigatus. A afmnt1 mutant is viable and grows normally at 37°C, but its hyphal cell wall appears to be thinner than that of the parental strain. The lack of AfMnt1 leads to a higher sensitivity to calcofluor white and Congo red but not to sodium dodecyl sulfate. The growth of the mutant is abrogated at 48°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 further revealed that the observed growth defect of the mutant at 48°C can be attributed to cell wall instability resulting in leakage at the hyphal tips. Using a red fluorescence fusion protein, we localized AfMnt1 in compact, brefeldin A-sensitive organelles that most likely represent fungal Golgi equivalents. The tumor necrosis factor alpha 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 afmnt1 mutant to azoles, antifungal agents that currently are used to treat Aspergillus infections, suggest that -1,2-mannosyltransferases are interesting targets for novel antifungal drugs.

Published ahead of print on 15 August 2008.