Site-Specific, Covalent Attachment of Proteins to a Solid Surface

Immobilized and site-specifically labeled proteins are becoming invaluable tools in proteomics. Here, we describe a strategy to attach a desired protein to a solid surface in a covalent, site-specific manner. This approach employs an enzymatic posttranslational modification method to site-specifically label a target protein with an azide; an alternative substrate for protein farnesyl transferase containing an azide group was developed for this purpose. A bio-orthogonal Cu(I)-catalyzed cycloaddition reaction is then used to covalently attach the protein to agarose beads bearing an alkyne functional group. We demonstrate that both the azide incorporation and the capture steps can be performed on either a purified protein target or on a protein present within a complex mixture. This approach involves the use of a four-residue tag which is significantly smaller than most other tags reported to date and results in covalent immobilization of the target protein. Hence it should have significant applicability in protein science.