EXPRESSION AND IDENTIFICATION OF A LAMININ-BINDING PROTEIN IN ASPERGILLUS-FUMIGATUS CONIDIA

Adhesion of Aspergillus fumigatus, the causative agent of human asperg illosis, to the extracellular matrix protein laminin has been previous ly demonstrated. This study investigated the expression of laminin rec eptors during swelling of conidia, a step leading to germination and s ubsequent colonization of tissues, Scanning electron microscopy showed that the laminin binding sites were distributed over the external rod let layer of resting conidia. During swelling, the characteristic rodl et layer progressively disintegrated and conidia surrounded by a smoot h cell wall layer appeared. Flow cytometry using fluorescein isothiocy anate-conjugated laminin demonstrated that expression of laminin recep tors at the surface of conidia was swelling dependent. Resting conidia expressed high levels of laminin receptors on their surface. A gradua l decrease of laminin binding was then observed as swelling occurred, reaching a minimum for 4-h-swollen conidia. This correlated with a los s of adherence of swollen conidia to laminin immobilized on microtiter plates. Trypsin pretreatment of conidia reduced laminin binding, Anal ysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ligand blotting with laminin identified in a cell wall extract a major 72-kDa cell wall glycoprotein which binds laminin. Thus, one of the i nitial events in the host colonization may be the recognition of basem ent membrane laminin by this 72-kDa cell wall surface component.