Inhibition of Aspergillus fumigatus conidia binding to extracellular matrix proteins by sialic acids: a pH effect?
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, alpha-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 alpha-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 alpha-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.
Tiralongo
Joe
J
Institute for Glycomics, Gold Coast Campus, Griffith University, QLD 4222, Australia.
Wohlschlager
Therese
T
Institute for Glycomics, Gold Coast Campus, Griffith University, QLD 4222, Australia.
Tiralongo
Evelin
E
School of Pharmacy, Gold Coast Campus, Griffith University, QLD 4222, Australia.
Kiefel
Milton J
MJ
Institute for Glycomics, Gold Coast Campus, Griffith University, QLD 4222, Australia.
D001228:Aspergillosis / Q000378:metabolism / Q000382:microbiology*; D001232:Aspergillus fumigatus / Q000187:drug effects* / Q000502:physiology; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D024141:Collagen Type IV / Q000378:metabolism*; D004271:DNA, Fungal / Q000032:analysis / Q000235:genetics; D005340:Fibrinogen / Q000378:metabolism*; D005965:Glucuronates / Q000494:pharmacology; D006023:Glycoproteins / Q000494:pharmacology; D054884:Host-Pathogen Interactions; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008172:Lung Diseases, Fungal / Q000378:metabolism / Q000382:microbiology*; D012689:Sequence Homology, Nucleic Acid; D012794:Sialic Acids / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D013172:Spores, Fungal / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*
D024141:Collagen Type IV; D004271:DNA, Fungal; D005965:Glucuronates; D006023:Glycoproteins; D012794:Sialic Acids; D005340:Fibrinogen