Aspergilli are one of the most common fungal species to which humans are exposed, and now these microorganisms are recognized as the most prevalent airborne fungal pathogen in developed countries. Among these species, the Aspergillus fumigatus is considered the most pathogenic. Thus, there is a compelling interest in the discovery of novel functional molecules and the pathways of new targets for antifungal drug development.
Acidic glycosphingolipid components were extracted from A. fumigatus and identified as glycosylinositol phosphorylceramides (GIPCs). By a combination of 1- and 2-D 1H-nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and gas chromatography/mass spectrometry (GC/MS), the structures of five major components were elucidated as:
Af-2: Manp(a1→3)Manp(a1→2)InsPCer
Af-3a: Galf(b1→6)Manp(a1→3)Manp(a1→2)InsPCer
Af-3b: Manp(a1→3)[Galf(b1→6)]Manp(a1→2)InsPCer
Af-4: Galf(b1→6)Manp(a1→3)[Galf(b1→6)]Manp(a1→2)InsPCer
Af-3c: Manp(a1→3)Manp(a1→6)GlcpN(a1→2)InsPCer
(Ins= myo-inositol, P= phosphodiester). A component containing a branching Galf(b1→6) residue, essentially identical to Af-3b, was previously isolated from the dimorphic mycopathogen Paracoccidioides brasiliensis, but component Af-3a has a novel isomeric glycosylinositol structure which was not previously identified in any fungal GIPCs. Af-4 is an additional novel component, bearing Galf(b1→6) on both Manp(a1→) residues of the common Af-2 core structure. Sera of patients with aspergillosis reacted strongly with Af-3a, -3b and -4 confirming the high antigenicity of fungi glycolipids containing terminal residues of galactofuranose. Also MEST-1, an anti-galactofuranose monoclonal antibody (mAb), reacts strongly with Af-3a, 3b and Af-4 present either in A. fumigatus strain 237 and 9197. On the other hand, mAb MEST-1 does not react with Af-2, Af-3c and with acidic glycolipids purified from A. nidulans (An-2, -3 and -5) as expected, since these glycolipids do not express galf in their structure.
Supported by FAPESP, CAPES, CNPq, Neose and NIH