Infection by Aspergillus fumigatus, which causes the life-threatening disease invasive aspergillosis, begins with the inhalation of conidia that adhere to and germinate in the lung. Previous studies have shown that A. fumigatus conidia express high levels of the negatively charged 9-carbon sugar sialic acid, and that sialic acid appears to mediate the binding of A. fumigatus conidia to basal lamina proteins. However, despite the ability of sialic acid to inhibit adherence of A. fumigatus conidia, the exact mechanism by which this binding occurs remains unresolved. Utilizing various free sialic acids and other carbohydrates, sialic acid derivatives, sialoglycoconjugates, glycoproteins, α-keto acid related compounds and amino acids we have found that the binding of A. fumigatus conidia to type IV collagen and fibrinogen was inhibited by (i) glycoproteins (in a sialic acid-independent manner), and (ii) free sialic acids, glucuronic acid and α-keto acid related compounds. However, inhibition by the latter was found to be the result of a shift in pH from neutral (pH 7.4) to acidic (less than pH 4.6) induced by the relatively high concentrations of free sialic acids, glucuronic acid and α-keto acid related compounds used in the binding assays. This suggests that previous reports describing inhibition of A. fumigatus conidia binding by free sialic acid may actually be due to a pH shift similar to that shown here. As previously reported, we found that A. fumigatus conidia express only N-acetylneuraminic acid, the most common sialic acid found in nature. However, A. fumigatus appears to do so by an alternative mechanism to that seen in other organisms. We report here that A. fumigatus (i) does not incorporate sialic acid obtained from the environment, (ii) does not synthesize and incorporate sialic acid from exogenous N-acetylmannosamine, and (iii) lacks homologues of known sialic acid biosynthesizing enzymes.
BromleyI. M.,
DonaldsonK.1996; Binding of Aspergillus fumigatus spores to lung epithelial cells and basement membrane proteins: relevance to the asthmatic lung. Thorax 51:1203–1209
HamiltonA. J.,
JeavonsL.,
YoungchimS.,
VanittanakomN.1999; Recognition of fibronectin by Penicillium marneffei conidia via a sialic acid-dependent process and its relationship to the interaction between conidia and laminin. Infect Immun 67:5200–5205
HaraS.,
YamaguchiM.,
TakemoriY.,
FuruhataK.,
OguraH.,
NakamuraM.1989; Determination of mono- O-acetylated N-acetylneuraminic acids in human and rat sera by fluorometric high-performance liquid chromatography. Anal Biochem 179:162–166
KepplerO. T.,
HorstkorteR.,
PawlitaM.,
SchmidtC.,
ReutterW.2001; Biochemical engineering of the N-acyl side chain of sialic acid: biological implications. Glycobiology 11:11R–18R
ManavathuE. K.,
AbrahamO. C.,
ChandrasekarP. H.2001; Isolation and in vitro susceptibility to amphotericin B, itraconazole and posaconazole of voriconazole-resistant laboratory isolates of Aspergillus fumigatus
. Clin Microbiol Infect 7:130–137
RodriguesM. L.,
RozentalS.,
CouceiroJ. N.,
AnglusterJ.,
AlvianoC. S.,
TravassosL. R.1997; Identification of N-acetylneuraminic acid and its 9- O-acetylated derivative on the cell surface of Cryptococcus neoformans: influence on fungal phagocytosis. Infect Immun 65:4937–4942
SchauerR.,
KamerlingJ. P.1997; Chemisty, biochemistry and biology of sialic acids. In Glycoproteins II pp 243–402 Edited by
MontreuilJ.,
VliegenthartJ. F. G.,
SchachterH.
Amsterdam: Elsevier;
SchillingB.,
GoonS.,
SamuelsN. M.,
GaucherS. P.,
LearyJ. A.,
BertozziC. R.,
GibsonB. W.2001; Biosynthesis of sialylated lipooligosaccharides in Haemophilus ducreyi is dependent on exogenous sialic acid and not mannosamine. Incorporation studies using N-acylmannosamine analogues, N-glycolylneuraminic acid, and 13C-labeled N-acetylneuraminic acid. Biochemistry 40:12666–12677
SoaresR. M.,
AlvianoC. S.,
AnglusterJ.,
TravassosL. R.1993; Identification of sialic acids on the cell surface of hyphae and yeast forms of the human pathogen Paracoccidioides brasiliensis
. FEMS Microbiol Lett 108:31–34
SoaresR. M. A.,
de A. SoaresR. M.,
AlvianoD. S.,
AnglusterJ.,
AlvianoC. S.,
TravassosL. R.2000Identification of sialic acids on the cell surface of Candida albicans Biochim Biophys Acta; 1474262–268
StevensD. A.,
KanV. L.,
JudsonM. A.,
MorrisonV. A.,
DummerS.,
DenningD. W.,
BennettJ. E.,
WalshT. J.,
PattersonT. F.,
PankeyG. A.2000; Practice guidelines for diseases caused by Aspergillus. Infectious Diseases Society of America. Clin Infect Dis 30:696–709
TronchinG.,
EsnaultK.,
RenierG.,
FilmonR.,
ChabasseD.,
BoucharaJ. P.1997; Expression and identification of a laminin-binding protein in Aspergillus fumigatus conidia. Infect Immun 65:9–15
WarwasM. L.,
WatsonJ. N.,
BennetA. J.,
MooreM. M.2007; Structure and role of sialic acids on the surface of Aspergillus fumigatus conidiospores. Glycobiology 17:401–410
WasylnkaJ. A.,
MooreM. M.2000; Adhesion of Aspergillus species to extracellular matrix proteins: evidence for involvement of negatively charged carbohydrates on the conidial surface. Infect Immun 68:3377–3384
WasylnkaJ. A.,
MooreM. M.2002; Uptake of Aspergillus fumigatus conidia by phagocytic and nonphagocytic cells in vitro: quantitation using strains expressing green fluorescent protein. Infect Immun 70:3156–3163
WasylnkaJ. A.,
SimmerM. I.,
MooreM. M.2001; Differences in sialic acid density in pathogenic and non-pathogenic Aspergillus species. Microbiology 147:869–877