Engineered protein A for the orientational control of immobilized proteins

This work describes the genetic engineering and characterization of a histidine-tagged fragment of protein A. The histidine tag results in the site-selective immobilization of the protein A receptor and the preservation of its high ligand affinity when immobilized on solid supports. The fragment was expressed at high yield in E. coli and purified to homogeneity. When selectively immobilized to histidine binding matrices, the protein A fragment exhibits high affinity for soluble IgG. We further demonstrate from adsorption isotherms that the receptor exhibits a homogeneous, high affinity population at densities where steric crowding between large ligands does not affect the apparent receptor affinity. This engineered receptor is appropriate for a range of applications including sensor design or those using immobilized Fc-tagged proteins.