The steroid carrier protein type 2 like (SCP-2L) domain of the human multifunctional enzyme 2 (MFE-2) has previously been used as a protein scaffold for both regioselective and enantioselective reactions using covalent modification through the introduction of unique cysteine residues . A number of residues in the scaffold's apolar tunnel (V83, A100, Q111) have previously been identified as being amenable to mutation and modification . Their location along the apolar tunnel provides an ideal starting point for the introduction of bipyridine into the protein scaffold to create an active site within a protein pocket. Three different sterol carrier proteins, each containing a unique cysteine at position Q111C, A100C or V83C, were prepared as described previously . Briefly, pEHISTEV plasmids containing the SCP gene inserted after an N-terminal His6 tag with TEV cleavage site were transformed into Rosetta DE3 E. coli cells. His6-tagged proteins were expressed in production broth media and purified by Ni-affinity chromatography with the His6 tag subsequently removed using TEV protease; a further purification step by Ni-affinity chromatography gave the final proteins in good yields (20-70 mgL -1 of media). Bipyridine was introduced into the protein scaffold through bioconjugation of the cysteine residues with 10 equivalents of 5-bromomethyl-2,2'bipyridine 1 in HEPES buffer at pH 8 (Figure ). The optimal conversion was approximately 70-85% modified protein, with minimal secondary modification (<5 % secondary modification; the remaining mass balance is unreacted protein, see Figure and ESIa Fig. ).