Surface-water Interface Induces Conformational Changes Critical for Protein Adsorption: Implications for Monolayer Formation of EAS Hydrophobin.

Kamron Ley,Matthew Penna,Dave Winkler,Andrew Christofferson,Shane Maclaughlin,Irene Yarovsky

doi:10.3389/fmolb.2015.00064

Abstract

The class I hydrophobin EAS is part of a family of small, amphiphilic fungal proteins best known for their ability to self-assemble into stable monolayers that modify the hydrophobicity of a surface to facilitate further microbial growth. These proteins have attracted increasing attention for industrial and biomedical applications, with the aim of designing surfaces that have the potential to maintain their clean state by resisting non-specific protein binding. To gain a better understanding of this process, we have employed all-atom molecular dynamics to study initial stages of the spontaneous adsorption of monomeric EAS hydrophobin on fully hydroxylated silica, a commonly used industrial and biomedical substrate. Particular interest has been paid to the Cys3-Cys4 loop, which has been shown to exhibit disruptive behavior in solution, and the Cys7-Cys8 loop, which is believed to be involved in the aggregation of EAS hydrophobin at interfaces. Specific and water mediated interactions with the surface were also analyzed. We have identified two possible binding motifs, one which allows unfolding of the Cys7-Cys8 loop due to the surfactant-like behavior of the Cys3-Cys4 loop, and another which has limited unfolding due to the Cys3-Cys4 loop remaining disordered in solution. We have also identified intermittent interactions with water which mediate the protein adsorption to the surface, as well as longer lasting interactions which control the diffusion of water around the adsorption site. These results have shown that EAS behaves in a similar way at the air-water and surface-water interfaces, and have also highlighted the need for hydrophilic ligand functionalization of the silica surface in order to prevent the adsorption of EAS hydrophobin.

Highlights

Microbial adhesion plays a pivotal role in contamination and degradation in a variety of areas, ranging from biomedical (Campoccia et al, 2013; Desrousseaux et al, 2013; Harding and Reynolds, 2014) to surface coating (Díaz et al, 2007; Hasan et al, 2013) and marine (Flemming, 2011; Kamino, 2013) applications
Our analyses will primarily focus on the systems that adsorbed at the surface-water interface, with particular emphasis on the behavior of the Cys3-Cys4 loop, Cys7-Cys8 loop and the role of interfacial water in the adsorption of EAS hydrophobin
In this work we have shown two possible binding motifs for EAS hydrophobin at a hydrated silica surface during the early spontaneous adsorption events identified by molecular dynamics (MD) simulations with atomic-level resolution

Summary

Introduction

Microbial adhesion plays a pivotal role in contamination and degradation in a variety of areas, ranging from biomedical (Campoccia et al, 2013; Desrousseaux et al, 2013; Harding and Reynolds, 2014) to surface coating (Díaz et al, 2007; Hasan et al, 2013) and marine (Flemming, 2011; Kamino, 2013) applications. The technologies to remove biofilms are improving considerably, there are significant limitations in reactive treatments due to the small length scales where biofilms are problematic Examples of this are evident in marine environments, where 25–50 μm biofilms on a ship hull increase hydrodynamic drag by 8–22% respectively (Townsin, 2003; Schultz et al, 2011), as well as health industries, where it is estimated that 20% of fatalities world-wide are due to infectious diseases, of which 80% are associated with biofilm formation (Prentice et al, 2004). Nanostructured surfaces with alternating hydrophobic/hydrophilic characteristics have recently been shown to be able to either promote or inhibit protein adsorption (Hung et al, 2011), the phenomenon can potentially be exploited to design surfaces resistant to biofouling

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