Magnetic beads are routinely used for separation steps in many downstream processes in biotechnology. Functionalization of magnetic beads that will specifically bind to analytes with high capacity and specificity supported by low unspecific binding is a desired feature in bio-separation, in vitro diagnostics and immune precipitation. A novel approach to functionalize magnetic beads is the usage of recombinant S-layer fusion proteins. Here, rSbpA31-1068ZZ exploiting the fragment crystallisable (Fc) antibody binding region of Protein A was used as a model system. The intrinsic property of S-layer proteins to self-assemble in a crystalline monomolecular array on solid supports is combined with the functionality of the genetically introduced moiety. The highly ordered rSbpA31-1068ZZ S-layer lattice also presents the binding sites for IgG in an oriented, exposed and reproducible way down to the nanometer range. The coating procedure, overall handling properties and the resulting IgG recoveries of various magnetic beads having different diameters ranging from 0.271-1.48 µm and different surface properties (-NH2, -COOH, epoxy groups) were investigated and compared. The rSbpA31-1068ZZ-coated beads could specifically bind and recover IgG in high purity within 30 minutes. No unspecific binding of serum components was observed on the bead surface confirming the expected anti-fouling properties of S-layer-coated solid phases.
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