Diffusion of hydrophobin proteins in solution and interactions with a graphite surface

In the simulations, HFBI exists in solution as a mixture of monomers in equilibrium with different types of oligomers. The oligomerization state depends on the conformation of HFBI. When a Highly Ordered Pyrolytic Graphite (HOPG) layer is present in the simulated system, HFBI tends to interact with the HOPG layer through a hydrophobic patch on the protein.From the simulations of HFBI solutions, we identify a tetrameric encounter complex stabilized by non-polar interactions between the aliphatic residues in the hydrophobic patch on HFBI. After the formation of the encounter complex, a local structural rearrangement at the protein interfaces is required to obtain the tetrameric arrangement seen in HFBI crystals. Simulations performed with the graphite surface show that, due to a combination of a geometric hindrance and the interaction of the aliphatic sidechains with the graphite layer, HFBI proteins tend to accumulate close to the hydrophobic surface.Hydrophobins are small (7-15 kDa) proteins produced by filamentous fungi [1]. They perform a range of biological roles including coating of spores and surface adhesion [2,3]. Except for Botrytis cinerea, where their function is unknown [4], hydrophobins lower the surface tension of water so that fungal hyphae can penetrate the air-water interface and grow outside aqueous media [5]. To carry out these functions, they rely on unique surface/interface binding properties [1,3,6-8]. Besides their peculiar surface properties, which make them the most powerful surface-active proteins known [3], they also display unusual behaviour in solution as they form different kinds of oligomers, depending on the conditions and on the hydrophobin type [9,10]. Hydrophobins have been divided into two classes, class I and class II, based on the hydropathy profile of the amino-acid sequence [1]. This classification is also consistent with other properties. In particular, class I hydrophobins are more resistant to dissociation using solvents and