Site-specific covalent labeling of His-tag fused proteins with a reactive Ni(II)-NTA probe

A new method for covalent labeling of a His-tag fused protein with a small reactive probe was developed; this method is based on the complementary interaction between the His-tag and Ni(II)-NTA, which facilitates a nucleophilic reaction between a histidine residue of the tag and the electrophilic tosyl group of the Ni(II)-NTA probe by the proximity effect.