Binding patterns of homo-peptides on bare magnetic nanoparticles: insights into environmental dependence

Magnetic nanoparticles (MNP) are intensively investigated for applications in nanomedicine, catalysis and biotechnology, where their interaction with peptides and proteins plays an important role. However, the characterisation of the interaction of individual amino acids with MNP remains challenging. Here, we classify the affinity of 20 amino acid homo-hexamers to unmodified iron oxide nanoparticles using peptide arrays in a variety of conditions as a basis to identify and rationally design selectively binding peptides. The choice of buffer system is shown to strongly influence the availability of peptide binding sites on the MNP surface. We find that under certain buffer conditions peptides of different charges can bind the MNP and that the relative strength of the interactions can be modulated by changing the buffer. We further present a model for the competition between the buffer and the MNP’s electrostatically binding to the adsorption sites. Thereby, we demonstrate that the charge distribution on the surface can be used to correlate the binding of positively and negatively charged peptides to the MNP. This analysis enables us to engineer the binding of MNP on peptides and contribute to better understand the bio-nano interactions, a step towards the design of affinity tags for advanced biomaterials

Design of Interactions Between Nanomaterials and Proteins: A Highly Affine Peptide Tag to Bare Iron Oxide Nanoparticles for Magnetic Protein Separation

Superparamagnetic nanoparticles have recently gained much attention due to their broad range of applicability including medical in vivo technologies, sensors and as supports for catalysts. As magnetic affinity materials, they can be utilized for the development of new purification strategies for pharmaceuticals and other target molecules from crude lysates. Here, a short peptide tag based on a glutamate sequence is introduced and the adsorption of pure protein as well as protein from crude cell lysate at different conditions is demonstrated. Fused to a model protein this tag can be used to recognize and purify this protein from a fermentation broth by bare iron oxide nanoparticles (BIONs). Binding of up to 0.2 g protein per g nanoparticles can be achieved and recovered easily by switching to a citrate buffered system. For a deeper understanding of the separation process, the aggregation and agglomeration of the nanoparticle protein systems were monitored for binding and elution steps. Furthermore, an upscaling of the process to the liter scale and the separation of a green fluorescent protein (GFP) containing the affinity tag to purities of 70% from E. coli fermentation broth was possible in a one step process by means of high gradient magnetic separation (HGMS)