The SC3 Hydrophobin Self-Assembles into a Membrane with Distinct Mass Transfer Properties

Abstract

Hydrophobins are a class of small proteins that fulfill a wide spectrum of functions in fungal growth and development. They do so by self-assembling into an amphipathic membrane at hydrophilic-hydrophobic interfaces. The SC3 hydrophobin of Schizophyllum commune is the best-studied hydrophobin. It assembles at the air-water interface into a membrane consisting of functional amyloid fibrils that are called rodlets. Here we examine the dynamics of SC3 assembly at an oil-water and air-water interface and the permeability characteristics of the assembled layer. Hydrophobin assembled at an oil-water interface is a dynamic system capable of emulsifying oil. It accepts soluble-state SC3 oligomers from water in a unidirectional process and sloughs off SC3 vesicles back into the water phase enclosing a portion of the oil phase in their hydrophobic interior. The assembled layer is impermeable to solutes >200 Da from either the water phase or the oil phase; however, due to the emulsification process, oil and the hydrophobic marker molecules in the oil phase can be transferred into the water phase, thus giving the impression that the assembled layer is permeable to the marker molecules. By contrast, the layer assembled at an air-water interface is permeable to water vapor from either the hydrophobic or hydrophilic side.

Crystal Structures of Hydrophobin HFBII in the Presence of Detergent Implicate the Formation of Fibrils and Monolayer Films

“…4f), indicating that the amphiphilic dimer might be a building block for the interfacial structures. The porous structure of the assembled hydrophobin layer, as suggested here, would also agree very well with the finding that the layers are permeable for small molecules (29).…”

“…the detergent, in order to form. For class I hydrophobin SC3, the formation of both 10-and 3-nm-thick layers has been reported (29,30), indicating multi-and monolayer, respectively. The formation of the layer is said to be concentrationdependent, and it has been found for SC3 that a featureless film is formed first and that after overnight incubation the 10-nm film with rodlet patterning forms (25).…”

Fungal and mushroom hydrophobins: A review

“…Another unique property of hydrophobins is their tendency to form very stable foams due to the high surface elasticity of membranes (Wang et al, 2005). The foaming tendency may be stronger for class II hydrophobins than for class I. Foams and bubble stability of HFBII was found stable for at least 4 months, and even up to several years in some cases at relatively low concentration of 0.1 wt% .…”

Organic-inorganic Interfaces for a New Generation of Hybrid Biosensors

“…Class I HFBs at low concentration are in monomeric form, while at higher concentrations they are mainly in a dimeric form (Wang, X et al, 2002;Wang, X et al, 2004). Self-assembly proceeds through the formation of an intermediate form, the -helical state (De Vocht, M.L et al, 2005, Wang, X et al, 2005. Upon transfer to the -sheet state, the content of -sheet structures increases.…”

“…However, during this transition the proteins forms nanometric wide fibrils, which are known as rodlets. SE measurements have shown that the film is about 3 nm thick (Wang, X et al, 2005). This and the fact that the diameter of the -barrel of the protein is approximately 2.5 nm suggest that the rodlets could be formed by a molecular monolayer (Kwan, A.H.Y et al, 2006).…”