Anchoring of histidine-tagged proteins to molecular printboards: self-assembly, thermodynamic modeling, and patterning

In this paper the multivalent binding of hexahistidine (His6)-tagged proteins to beta-cyclodextrin (beta-CD) self-assembled monolayers (SAMs) by using the nickel(II) complex of a hetero-divalent orthogonal adamantyl nitrilotriacetate linker (4) is described. Nonspecific interactions were suppressed by using monovalent adamantyl-hexa(ethylene glycol) derivative 3. With the mono-His6-tagged maltose binding protein (His6-MBP), thermodynamic modeling based on surface plasmon resonance (SPR) titration data showed that the MBP molecules in solution were linked, on average, to Ni.4 in 1:1 stoichiometry. On the surface, however, the majority of His(6)-MBP was complexed to surface-immobilized beta-CDs through three Ni.4 complexes. This difference is explained by the high effective beta-CD concentration at the surface and is a new example of supramolecular interfacial expression. In a similar adsorption scheme, SPR proved that the alpha-proteasome could be attached to beta-CD SAMs in a specific manner. Patterning through microcontact printing of (His6)4-DsRed-fluorescent timer (DsRed-FT), which is a tetrameric, visible autofluorescent protein, was carried out in the presence of Ni.4 Fluorescence measurements showed that the (His6)4-DsRed-FT is bound strongly through Ni.4 to the molecular printboard.