Hydrophobins are surface active proteins produced by filamentous fungi. They have a role in fungal growth as structural components and in the interaction of fungi with their environment. They have, for example, been found to be important for aerial growth, and for the attachment of fungi to solid supports. Hydrophobins also render fungal structures, such as spores, hydrophobic. The biophysical properties of the isolated proteins are remarkable, such as strong adhesion, high surface activity and the formation of various self-assembled structures. The first high resolution three dimensional structure of a hydrophobin, HFBII from Trichoderma reesei, was recently solved. In this review, the properties of hydrophobins are analyzed in light of these new data. Various application possibilities are also discussed.

Hydrophobins are proteins specific to filamentous fungi. Hydrophobins have several important roles in fungal physiology, for example, adhesion, formation of protective surface coatings, and the reduction of the surface tension of water, which allows growth of aerial structures. Hydrophobins show remarkable biophysical properties, for example, they are the most powerful surface-active proteins known. To this point the molecular basis of the function of this group of proteins has been largely unknown. We have now determined the crystal structure of the hydrophobin HFBII from Trichoderma reesei at 1.0 Å resolution. HFBII has a novel, compact single domain structure containing one ␣-helix and four antiparallel ␤-strands that completely envelop two disulfide bridges. The protein surface is mainly hydrophilic, but two ␤-hairpin loops contain several conserved aliphatic side chains that form a flat hydrophobic patch that makes the molecule amphiphilic. The amphiphilicity of the HFBII molecule is expected to be a source for surface activity, and we suggest that the behavior of this surfactant is greatly enhanced by the selfassembly that is favored by the combination of size and rigidity. This mechanism of function is supported by atomic force micrographs that show highly ordered arrays of HFBII at the air water interface. The data presented show that much of the current views on structure function relations in hydrophobins must be re-evaluated.

The cellulase and hemicellulase genes of the filamentous fungus Trichoderma reesei have been shown to be under carbon catabolite repression mediated by the regulatory gene cre1. In this study, strains were constructed in which the cre1 gene was either completely removed or replaced by a truncated mutant variant, cre1-1, found previously in the Rut-C30 mutant strain with enhanced enzyme production capability. The T. reesei transformants with either deletion or truncation of cre1 had clearly altered colony morphology compared with the parental strains, forming smaller colonies and fewer aerial hyphae and spores. Liquid cultures in a medium with glucose as a carbon source showed that the transformants were derepressed in cellulase and hemicellulase production. Interestingly, they also produced significantly elevated levels of these hydrolytic enzymes in fermentations carried out in a medium inducing the hydrolase genes. This suggests that cre1 acts as a modulator of cellulase and hemicellulase gene expression under both noninducing and inducing conditions. There was no phenotypic difference between the ⌬cre1 and cre1-1 mutant strains in any of the experiments done, indicating that the cre1-1 gene is practically a null allele. The results of this work indicate that cre1 is a valid target gene in strain engineering for improved enzyme production in T. reesei.The filamentous fungus Trichoderma reesei (Hypocrea jecorina) produces large amounts of extracellular enzymes. The majority of the secreted proteins are various plant polymerdegrading enzymes; the most abundant of these enzymes are the cellobiohydrolases and endoglucanases that act synergistically to break down cellulose. This fungus has been used as a production host for various industrial enzymes, including products tailored for textile, feed, food, and pulp and paper applications (6, 10). It has been reported that protein production levels in the industrial T. reesei process exceed 100 g/liter (7).The major cellulase and hemicellulase genes are regulated in a coordinate manner by the carbon source available (2, 9, 14). Cellulose and other plant materials and other substances (for example, lactose) induce the expression of cellulase and hemicellulase genes, while glucose acts as a repressing carbon source. Several genes coding for regulators of cellulase and hemicellulase expression have been isolated. These include CREI mediating carbon catabolite repression, the repressor ACEI, the activator ACEII, the CCAAT binding complex Hap2/3/5 (reviewed in references 2, 17, and 27) and the activator XYRI (29). The CREI protein has sequence similarity with other fungal proteins mediating glucose repression, such as Aspergillus nidulans CREA (8) and Saccharomyces cerevisiae MIG1 and RGR1 (22). In T. reesei, glucose repression has been shown to occur upon binding of CREI to specific sequences in the cbh1 promoter (13). A mutant cre1 gene (cre1-1) encoding a truncated form of CREI has been isolated from the hypercellulolytic T. reesei strain Rut-C30, which is capable of cel...

Fungal infection of barley and malt, particularly by strains of the genus Fusarium, is known to be a direct cause of beer gushing. We have shown previously that small fungal proteins, hydrophobins, isolated from strains of the genera Fusarium, Nigrospora and Trichoderma act as gushing factors in beer. A hydrophobin concentration as low as 0.003 ppm was sufficient to induce gushing. The gushing-inducing abilities of the isolated hydrophobins varied probably due to their structural differences. The hydrophobins did not affect beer foam stability. A correlation was observed between the hydrophobin level analyzed by the hydrophobin ELISA developed and the gushing potential of malt. The risk of gushing was found to increase with hydrophobin concentrations above 250 µg/g malt. The levels of hydrophobin and the Fusarium mycotoxin deoxynivalenol (DON) in malts were not correlated which indicated that the formation of those two fungal metabolites may not be linked. Furthermore, we did not observe a correlation between the DON content and the gushing potential of the malt studied. Our observations suggest that the accuracy of predicting gushing could be improved by measuring the amount of the actual gushing factors, hydrophobins, in barley or malt.