Novel purification system for 6xHis-tagged proteins by magnetic affinity separation

We have developed a novel nickel–silica matrix for the generation of magnetic beads for metal-ion affinity chromatography. In contrast to magnetic Ni–NTA agarose beads, the novel particle type (SiMAC) consists of a magnetic core and a nickel–silica composite matrix with the nickel ions tightly integrated in the silica. This results in a much higher number of chelating groups compared with Ni–NTA agarose beads. With the SiMAC beads, greatly improved purification of histidine-tagged proteins from crude bacterial extracts was achieved. The yield was at least twice as high as with conventional materials, the method is faster, since the coupling step is omitted and there is no need for handling toxic Ni2+ salts.