Abstract
Class I hydrophobins function in fungal growth and development by self-assembling at hydrophobic-hydrophilic interfaces into amyloid-like fibrils. SC3 of the mushroom-forming fungus Schizophyllum commune is the best studied class I hydrophobin. This protein spontaneously adopts the amyloid state at the water-air interface. In contrast, SC3 is arrested in an intermediate conformation at the interface between water and a hydrophobic solid such as polytetrafluoroethylene (PTFE; Teflon). This finding prompted us to study conditions that promote assembly of SC3 into amyloid fibrils. Here, we show that SC3 adopts the amyloid state at the water-PTFE interface at high concentration (300 microg ml(-1)) and prolonged incubation (16 h). Moreover, we show that amyloid formation at both the water-air and water-PTFE interfaces is promoted by the cell wall components schizophyllan (beta(1-3),beta(1-6)-glucan) and beta(1-3)-glucan. Hydrophobin concentration and cell wall polysaccharides thus contribute to the role of SC3 in formation of aerial hyphae and in hyphal attachment.
Highlights
Hydrophobins share eight conserved cysteine residues, but otherwise their sequences are diverse (4)
X-ray diffraction of rodlets of EAS showed reflections at 4.8 Å and 10 –12 Å (19), which are indicative for amyloid fibrils
Foam that had formed during electrobubbling in the presence or absence of 1 mg mlϪ1 schizophyllan was freeze-dried, after which 100 l of water was added to 200 g of the freeze-dried material
Summary
Hydrophobins share eight conserved cysteine residues, but otherwise their sequences are diverse (4). SC3 of Schizophyllum commune is the best characterized class I hydrophobin It self-assembles at interfaces between water and air, water and oil, and water and hydrophobic solids (6 – 8). Like other amyloid fibrils (16), rodlets of the hydrophobins SC3 of S. commune and EAS of Neurospora crassa increase fluorescence of thioflavin T and bind Congo red (14, 17, 18). SC3 does not spontaneously self-assemble into amyloid fibrils at an interface between water and a hydrophobic solid. Transition to the -sheet state is observed only by heating the sample in the presence of detergent (11, 12). These observations prompted us to study conditions that promote assembly of SC3 into amyloid fibrils. We show that amyloid formation of SC3 is promoted by increasing its concentration or by the presence of cell wall polysaccharides
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