Proteins are important actors within a cell, therefore, necessary for all lives on earth. Proteins are responsible for building our bodies, transmitting signals and play a key role in the human immune system. In addition, proteins are important in the production of a number of products especially in the dairy, bakery, and meat industries. Protein deposition and aggregation, which a common phenomenon can result in challenging issues in the industry. In the dairy industry, for instance, protein fouling in heat exchangers can lead to significant energy loss, high operational cost, and even serious food safety problems.
Studies on the structure of proteins have shown that changing the pH, ion strength with additional Ca2+ or S2- ion, surface chemistry with varying forms of polymers under varying fluid conditions, for instance, impinging jet flow as well as turbulent flow, would affect the process of adsorption. Experimental analyses have also demonstrated that acidic amino acid residues possess strong affinity to the surface and can provide a contribution to adsorption.
Considering that, it is challenging to get localized and dynamic experimental data, whether the protein deposit results from discrete unfold protein or even the segregated mixture is not clear. The fundamental understanding of the protein adsorption mechanisms is incomplete.
In the past years, researchers have embarked on computer simulations. They have focused on molecular simulations of protein adsorption and have identified interaction potentials between different parts in the peptide and the surface. Unfortunately, most of these studies have focused on the lockdown phase, while only a few can be identified for the phases before locking down, that ought to be critical for understating the key factors that lead to protein diffusion towards the surface.
Researchers from Soochow University (China), Prof. Xiao Dong Chen, Prof. Jie Xiao, and Ms. Ruosang Qiu (currently a PhD student at Monash University, Australia), developed simulation models as well as quantitative analysis models that could answer the scientific questions in the analysis of peptide adsorption on a water interacting uncharged solid surface. This study resorted to a unique mesoscale modelling method. Their work is published in journal, Colloids and Surfaces A: Physicochemical and Engineering Aspects.
The authors developed a new coarse-grained model that coupled the MARTINI force field and Lattice Monte Carlo Bond Fluctuation model to simulate peptide adsorption onto strongly water interacting uncharged surfaces. By resorting to this model, they then proposed a new mechanism for the biased diffusion phenomena: the net attractive forces that pull beads initially situated beyond the reach of the substrate surface interaction towards the surface, are LJ forces initiated by the water layers. The forces could become one order of magnitude larger than electrostatic forces.
The coarse-grained lattice model has inherent limitations such as implicit bond interactions and restricted bead locations. However, the developed model could predict successfully the biased diffusion phenomenon while quantitative analyses on force partitioning could support the mechanism highlighted in the current study.
The mesoscale coarse-grained model developed in their study will be expected to be a useful tool in the future to investigate protein adsorption beyond the case where only one short peptide is considered. It will be especially useful for the in-depth fundamental understanding of protein fouling, and help identify effective anti-fouling strategies for the dairy industry.
Ruosang Qiu, Jie Xiao, Xiao Dong Chen. Further understanding of the biased diffusion for peptide adsorption on uncharged solid surfaces that strongly interact with water molecules. Colloids and Surfaces A: Physicochemical. Eng. Aspects, volume 518 (2017), pages 197–207.
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