Abstract
In situ fibrillation of plant proteins in presence of the superparamagnetic iron oxide nanoparticles (NP) promoted formation of a hybrid nanocomposite. The morphology of NP-fibril composite was revealed using ex-situ atomic force microscopy (AFM) in air. The NP-fibrils were associated into extended multi-fibril structures, indicating that the addition of NPs promoted protein association via β-sheet assembly. Real-time movement of NPs attached to fibrils under an external magnetic field was visualized using in-situ AFM in liquid, revealing that composite structures were stable at low pH, and displaying dipolar property of the NPs in the composite at high pH. Changes in magnetic properties of NPs when interacting with protein fibrils were quantitatively mapped using magnetic force microscopy (MFM). The magnetic moment of the NPs in composite was increased by co-existing with protein at low pH, while their dipolar nature was maintained at high pH. Self-assembly of the protein into fibrils is accelerated with increasing NP concentration within an optimal range, which is attributed to a fibrillation-competent conformation of the peptides. The latter was explained by the formation of favorable hydrogen bonds, electrostatic interactions, and efficient surface energy transfer between NPs and proteins.
Highlights
Proteins display a strong propensity to adsorb onto surfaces via electrostatic interactions, coordinative bonds, hydrogen bonds, and hydrophobic interactions
In a recent study on the role of peptide hydrolysis in bovine whey protein β-lactoglobulin fibrillation kinetics, we demonstrated that the balance between protein concentration and hydrolysis rate determined the structure of the amyloid fibrils formed[15]
As confirmed by the Fourier transform infrared (FTIR) results, we could conclude that introduction of NPs significantly increased the formation of β-type secondary structure and self-assembly of the long protein fibrils, which was related to conformational changes
Summary
Proteins display a strong propensity to adsorb onto surfaces via electrostatic interactions, coordinative bonds, hydrogen bonds, and hydrophobic interactions. This study provided insights on the controlled self-assembly of proteins into novel nanomaterials by further understanding the mechanism of nucleation kinetics between protein and NPs. there has been growing interest in the study of amyloid-like fibril assembly within the fields of materials science, owing to advanced functionalities related to their structural polymorphism and specific physicochemical properties[8]. Studies on magnetic responsive composite materials using β-lactoglobulin-based amyloid fibrils and iron oxide NPs (Fe3O4) have provided great promise in design of functional colloidal systems, in which the aggregation behavior, orientational order of the composite were efficiently controlled in a purely noninvasive way by moderate magnetic fields of weak intensity[16,17] Tuning of NP biological functionality can be achieved through controlled surface chemistry by manipulating the surface properties of the NPs at the bioconjugated interface between NP and protein surface[18]. Even though extensive physicochemical characterization of targeting NPs can be addressed in detail, relevant quantitative biological characterization for real time study of the nano-interface is challenging for selecting suitable nanomaterials for further in vitro or in vivo experiments[21]
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