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Protein HGFI from the edible mushroom Grifola frondosa is a novel 8 kDa class I hydrophobin that forms rodlets in compressed monolayers

Lei Yu^1,2,

Géza R. Szilvay^2,

¹ College of Life Sciences, Nankai University, No. 94 Weijin Road, Tianjin 300071, PR China
² VTT Biotechnology, Technical Research Centre of Finland, PO Box 1000, FI-02044 VTT, Finland
³ University of Joensuu, Department of Chemistry, PO Box 111, FI-80101 Joensuu, Finland

Correspondence
Mingqiang Qiao
mingqiangqiao{at}yahoo.com.cn
Markus B. Linder
Markus.linder{at}vtt.fi

Hydrophobins are a group of low-molecular-mass, cysteine-rich proteins that have unusual biophysical properties. They are highly surface-active and can self-assemble at hydrophobic–hydrophilic interfaces, forming surface layers that are able to reverse the hydropathy of surfaces. Here we describe a novel hydrophobin from the edible mushroom Grifola frondosa, which was named HGFI and belongs to class I. The hydrophobin gene was identified during sequencing of random clones from a cDNA library, and the corresponding protein was isolated as a hot SDS-insoluble aggregate from the cell wall. The purified HGFI was found to have 83 amino acids. The protein sequence deduced from the cDNA sequence had 107 amino acids, from which a 24 aa signal sequence had been cleaved off in the mature protein. This signal sequence was 5 aa longer than had been predicted on the basis of signal peptide analysis of the cDNA. Rodlet mosaic structures were imaged using atomic force microscopy (AFM) on mica surfaces after drying-down HGFI solutions. Using Langmuir films we were also able to take images of both the hydrophobic and hydrophilic sides of films formed at the air–water interface. No distinct structure was observed in films compressed once, but in films compressed several times rodlet structures could be seen. Most rodlets were aligned in the same direction, indicating that formation of rodlets may be promoted during compression of the monolayer.

Present address: Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, PR China.

Present address: Columbia University, 500 W 120th Street, NY 10027, USA.

The GenBank/EMBL/DDBJ accession number for the genomic hgf1 sequence of Grifola frondosa is EF486307.