A Supramolecular Host-Guest Carrier System for Growth Factors Employing VHH Fragments

A supramolecular strategy is presented for the assembly of growth factors employing His(6)-tagged single-domain antibodies (VHH). A combination of orthogonal supramolecular interactions of beta-cyclodextrin (beta CD)adamantyl (Ad) hostguest and N-nitrilotriacetic acid (NTA)histidine (His) interactions was employed to generate reversible and homogeneous layers of growth factors. A single-domain antibody VHH fragment was identified to bind to the human bone morphogenetic protein-6 (hBMP6) growth factor and could be recombinantly expressed in E. coli. The VHH fragment was equipped with a C-terminal hexahistidine (His(6)) tether to facilitate the assembly on beta CD surfaces using a linker that contains an Ad group to bind to the beta CD receptors and an NTA moiety to interact with the His(6)-tag upon cocomplexation of Ni2+ ions. After exploring the thermodynamic and kinetic stability of the VHH assemblies on beta CD surfaces using a variety of experimental techniques including microcontact printing (mu CP), surface plasmon resonance (SPR), microscale thermophoresis (MST), and theoretical models for determining the thermodynamic behavior of the system, hBMP6 was assembled onto the VHH-functionalized surfaces. After analyzing the immobilized hBMP6 using immunostaining, the biological activity of hBMP6 was demonstrated in cell differentiation experiments. Early osteogenic differentiation was analyzed in terms of alkaline phosphatase (ALP) activity of KS483-4C3 mouse progenitor cells, and the results indicated that the reversibly immobilized growth factors were functionally delivered to the cells. In conclusion, the supramolecular strategy used here offers the necessary affinity, reversibility, and temporal control to promote biological function of the growth factors that were delivered by this strategy.