Fishing for Proteins with Magnetic Cellulosic Nanocrystals

摘要

A key to proteomics exploitation is magnetic separation of target proteins in a sea of others. The process is similar to fishing, where the target protein is like a specific type offish. An antigen, covalently linked on a magnetic nanocrystal, is "the bait and hook"; the fishing line is simulated by an applied magnetic field. By selective binding the target protein can be caught, isolated and released from the nanocrystal support once the interaction of antigen-antibody is neutralized. Microcrystalline cellulose (MCC) is responsive to functionalization, as required to tether the desirable bioactive ligand. Chitin nanocrystals with some free surface amino groups are also as suitable as nanocrystal support. To render MCC magnetic, ferrous iron is adsorbed and converted to ferrous hydroxide, which is then oxidized with KNOj to form superparamagnetic magnetite. From the magnetization curves, the particle size distribution and magnetite content of ferrites in the polysaccharide matrix can be derived. A trial fishing experiment to isolate a target protein used a magnetized MCC platform to which Protein A, a specific ligand of Immunoglobulin G, IgG, was attached. The resulting magnetic platform, captured the target IgG which was magnetically separated from the supernatant. IgG was isolated by screening the non-bonded interactions between IgG and its specific ligand.