GENETIC AND BIOCHEMICAL-CHARACTERIZATION OF THE TRICHODERMA-REESEI HYDROPHOBIN HFBI

The hfbI gene of the filamentous fungus Trichoderma reesei, previously cloned as a gene which was abundantly expressed when the fungus was g rown on glucose-containing medium, was shown to encode a novel fungal hydrophobin. The encoded 97-amino-acid protein is cysteine-rich and ha s a typical signal sequence for secretion. Signal-sequence cleavage an d putative proteolytic processing results in the mature HFBI protein o f 75 amino acids. Antibodies raised against the HFBI protein expressed in Escherichia coli detected the T. reesei HFBI protein in the fungal cell wall and in the culture medium of submerged glucose-containing c ultures. The identity of HFBI was verified by N-terminal and peptide s equencing of proteins purified both from the cell wall and culture med ium. In the cell wall most of the HFBI formed SDS-insoluble complexes that could be extracted with trifluoroacetic acid. Bubbling or freezin g of the culture medium caused HFBI to form aggregates that coprecipit ated with a yellow pigment produced by the fungus.