Structural changes and molecular interactions of hydrophobin SC3 in solution and on a hydrophobic surface

Abstract

The hydrophobin SC3 belongs to a class of small proteins functioning in the growth and development of fungi. Its unique amphipathic property and remarkable surface activity make it interesting not only for biological studies but also for medical and industrial applications. Biophysical studies have revealed that SC3 possesses at least three distinct conformations, named "soluble-state SC3" for the protein in solution, and "␣-helical-state SC3" and "␤-sheet-state SC3" for the different states of the protein associated at a hydrophobic-water interface. The present fluorescence study shows that the microenvironment of the dansyl-labeled N terminus of soluble-state SC3 is relatively hydrophobic, whereas it is hydrophilic for ␣-helical-state and ␤-sheet-state SC3. Fluorescence collisional quenching indicates that the N terminus of soluble-state SC3 is more solvent-accessible than those of ␣-helical-state and ␤-sheet-state SC3, with Stern-Volmer constants for acrylamide of 4.63, 0.02, and 0.2 M −1 for the different states, respectively. Fluorescence resonance energy transfer measurements show that soluble-state SC3 tends to associate in solution but dissociates in TFA. Fluorescence energy transfer was eliminated by conversion of soluble-state SC3 to ␣-helical-state SC3 on a hydrophobic surface, indicating a spatial separation of the molecules in this state. By inducing the ␤-sheet state, structural changes were observed, both by CD and by fluorescence, that could be fit to two exponentials with lifetimes of about 10 min and 4 h. Molecules in the ␤-sheet state also underwent a slow change in spatial proximity on the hydrophobic surface, as revealed by the reappearance of fluorescence resonance energy transfer in time.Keywords: Hydrophobin; circular dichroism spectroscopy; fluorescence collisional quenching; fluorescence resonance energy transfer Hydrophobins are a class of small proteins that play an important role in fungal growth and development, for example, the formation of aerial hyphae and the attachment of hyphae to hydrophobic surfaces (Wösten et al. , 1994avan Wetter et al. 1996van Wetter et al. , 2000. These proteins are remarkable in that they self-assemble into an amphipathic membrane at hydrophobic-hydrophilic interfaces. This makes them interesting not only from a biological point of view, but also for medical and industrial applications (Wessels 1997;Scholtmeijer et al. 2001). Two different types of hydrophobins, class I and class II, have been distinguished based on the differences in their hydropathy patterns and biophysical properties (Wessels 1994).SC3, secreted by Schizophyllum commune, is the best characterized class I hydrophobin. It contains eight cysteine Reprint requests to: G.T. Robillard, BioMaDe Technology Foundation, Nijenborgh 4, 9747 AG Groningen, The Netherlands; e-mail: Robillard@ biomade.nl; fax: 031-50-3634321.Abbreviations: CD, circular dichroism spectroscopy; ATR-FTIR, attenuated total reflection-Fourier transform infrared spectroscopy; TFA, trifluoroacetic acid; FRET, fluor...

The relation between solution association and surface activity of the hydrophobin HFBI from Trichoderma reesei

“…The extent to which solution association affects surface activity is not well understood. There is a large conformational change associated with SC3 surface self-assembly [24,30], that is absent in the class II hydrophobin HFBI [31], making it difficult to compare the two classes.…”

“…2) [22][23][24][25]. HFBI associates in solution into tetramers which have been proposed to be formed mainly by the driving force of hydrophobic interactions between the hydrophobic patches [23].…”

Applications of hydrophobins: current state and perspectives

“…Monomers or dimers normally represent the water-soluble forms of class I hydrophobins (Mackay et al 2001;Wang et al 2002Wang et al , 2004bMorris et al 2013). However, the Vmh2 hydrophobin (Pleurotus ostreatus) is only soluble in complexes with glycans (Armenante et al 2010).…”

Assembly of the Fungal SC3 Hydrophobin into Functional Amyloid Fibrils Depends on Its Concentration and Is Promoted by Cell Wall Polysaccharides

“…The water-soluble form of SC3 is oligomeric (10) and rich in ␤-sheet (11). Upon assembly at the water-air interface, SC3 proceeds via an intermediate form that has increased ␣-helical structure (␣-helical state) to a stable end form that has increased ␤-sheet structure (␤-sheet state) (11)(12)(13).…”