INTERACTION BETWEEN ASPERGILLUS-FUMIGATUS AND BASEMENT-MEMBRANE LAMININ - BINDING AND SUBSTRATE DEGRADATION

Aspergillus fumigatus, the causative agent of human aspergillosis, bin ds to and degrades basement membrane laminin. Using immunoelectron mic roscopy, laminin binding appeared to be associated with the cell wall expansions of resting conidia, and progressively extended to the outer electron dense layer of the conidial wall during the germination proc ess. Labeling of thin sections revealed numerous binding sites in the cytoplasm, whereas the inner cell wall and the plasma membrane were no t labeled. Attachment of A fumigatus conidia on microtiter plates coat ed with laminin and its fragments P1 and E8 was also investigated. Con idia cells showed good adhesion to wells coated with laminin. As indic ated by inhibition experiments, the interaction was specific and fragm ent P 1 represented the major binding site on the laminin molecule. In addition, since A fumigatus produced an extracellular serine protease , we determined the susceptibility of laminin to this enzyme. We demon strated that a crude protease extract was capable to degrade laminin i n solution as well as in tissue sections. The laminin cleavage product s were detected by sodium dodecyl sulfate-polyacrylamide gel electroph oresis. All the three chains were extensively degraded within 1 h. Tre atment of the crude protease extract with the enzyme inhibitors, pheny lmethylsulfonyl-fluoride and chymostatin, blocked the degradation of l aminin, indicating a chymotrypsin-like serine protease activity. Immun ofluorescence microscopy of cryostat sections of mouse and rat kidneys treated with the protease extract showed widespread loss of laminin e pitopes from basement membranes. Enzyme treatment also removed immunor eactivity from lungs as observed after immunoperoxidase performed on p araffin sections. Binding and proteolytic degradation of laminin may t ogether facilitate initial interaction of A fumigatus with the host ti ssues.