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

Ley K, Christofferson A, Penna M, Winkler D, Maclaughlin S, Yarovsky I - Front Mol Biosci (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Health Innovations Research Institute and School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University Melbourne, VIC, Australia.

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.

No MeSH data available.


Average number of contacts with the surface for EAS over the last 10 ns of simulation in binding motif (A) 1 and (B) 2. Colors are matched to the residue-surface distance plots in Figure 2 and represent different simulation runs. Heavy atoms of a given residue are considered in contact with the surface if they fall within 4.5 Å of any surface atom.
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Figure 3: Average number of contacts with the surface for EAS over the last 10 ns of simulation in binding motif (A) 1 and (B) 2. Colors are matched to the residue-surface distance plots in Figure 2 and represent different simulation runs. Heavy atoms of a given residue are considered in contact with the surface if they fall within 4.5 Å of any surface atom.

Mentions: To date there have been several studies by Walsh and colleagues on how the spacing of hydroxyl groups on silica surfaces effects the behavior of interfacial water, and how that influences the binding of hydrophobic and hydrophilic molecules and peptides (Notman and Walsh, 2009; Oren et al., 2010). Importantly, these works highlighted that larger spacing of hydroxyl groups on the surface would result in areas void of water. Free energy calculations have shown that it was energetically favorable for small hydrophobic moieties like methane to penetrate into these voids, where they would then be shielded by the surface interfacial water. This phenomenon was further explored on amorphous silica models with atomistic roughness, similar to those used in this study, by Schneider and Ciacchi (2012). In this study it was noted that these hydrophobic voids were present in larger volume due to surface cavities, which allowed penetration of hydrophobic side chains. On peptides which had alternating hydrophilic and hydrophobic residues, similar to those on EAS hydrophobin, it was noticed that adsorption was significantly enhanced as the hydropathicity of the interfacial water and voids could be matched, as well as allowing increased electrostatic interactions with the surface. In our simulations of EAS with the atomistically rough amorphous silica surface, we do indeed notice this phenomenon occurring. The average number of contacts for residues in contact with the surface during the last 20 ns of simulations for both binding motifs is presented in Figure 3.


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

Ley K, Christofferson A, Penna M, Winkler D, Maclaughlin S, Yarovsky I - Front Mol Biosci (2015)

Average number of contacts with the surface for EAS over the last 10 ns of simulation in binding motif (A) 1 and (B) 2. Colors are matched to the residue-surface distance plots in Figure 2 and represent different simulation runs. Heavy atoms of a given residue are considered in contact with the surface if they fall within 4.5 Å of any surface atom.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4644811&req=5

Figure 3: Average number of contacts with the surface for EAS over the last 10 ns of simulation in binding motif (A) 1 and (B) 2. Colors are matched to the residue-surface distance plots in Figure 2 and represent different simulation runs. Heavy atoms of a given residue are considered in contact with the surface if they fall within 4.5 Å of any surface atom.
Mentions: To date there have been several studies by Walsh and colleagues on how the spacing of hydroxyl groups on silica surfaces effects the behavior of interfacial water, and how that influences the binding of hydrophobic and hydrophilic molecules and peptides (Notman and Walsh, 2009; Oren et al., 2010). Importantly, these works highlighted that larger spacing of hydroxyl groups on the surface would result in areas void of water. Free energy calculations have shown that it was energetically favorable for small hydrophobic moieties like methane to penetrate into these voids, where they would then be shielded by the surface interfacial water. This phenomenon was further explored on amorphous silica models with atomistic roughness, similar to those used in this study, by Schneider and Ciacchi (2012). In this study it was noted that these hydrophobic voids were present in larger volume due to surface cavities, which allowed penetration of hydrophobic side chains. On peptides which had alternating hydrophilic and hydrophobic residues, similar to those on EAS hydrophobin, it was noticed that adsorption was significantly enhanced as the hydropathicity of the interfacial water and voids could be matched, as well as allowing increased electrostatic interactions with the surface. In our simulations of EAS with the atomistically rough amorphous silica surface, we do indeed notice this phenomenon occurring. The average number of contacts for residues in contact with the surface during the last 20 ns of simulations for both binding motifs is presented in Figure 3.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Health Innovations Research Institute and School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University Melbourne, VIC, Australia.

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.

No MeSH data available.