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Artificial proteins trained as nano-goldsmiths

Artificial proteins selected for their chemical affinity for gold and their specific structural recognition of (111) atomic planes prove to be highly effective in controlling the growth of exclusively (111)-facetted nanocrystals. Strongly bound to the facets, they can be modified to induce colloidal self-assembly or on-surface enzymatic catalysis.

Darwinian evolution explains the emergence of proteins that chaperone the growth and morphogenesis of biominerals (Ex. : enamel, bone, nacre) and dictate their surface properties.
Directed evolution is a combinatorial biochemical tool that mimic Darwinian evolution. Libraries of billions of peptides or antibodies, all distinct from each other and each embedded on a bacteriophage virus are built. When the bacteriophage population is exposed to a target (Ex. a pathologic antigen), directed evolution enables the identification of the few individuals, among several billions, that bind most strongly ("have the highest affinity") to the target. The peptide or antibody responsible for this extremely specific chemical recognition can then be synthesized. Directed evolution has revolutionized analytic and therapeutic biochemistry and has earned F. Arnold, G. Smith and G. Winter the Nobel Prize in Chemistry 2018. Yet, it is almost impossible for a flexible peptide or antibody to distinguish a specific crystalline order.

Directed evolution has been applied, for the first time, by two teams from CEMES (Toulouse) and IB2C (Orsay), to a library of fully folded artificial proteins exposed to the (111) atomic planes of crystalline gold surface.

Artificial repeat proteins are selected by directed evolution for their high chemical affinity for gold and structural selectivity for (111) facets. The proteins chaperone the growth of (111)-terminated nanocrystals and form a functional shell.

The library, built by the team of Philippe Minard, comprises about 2 billions repeat proteins that share a scaffold made of concatenated double alpha helix modules, which endows them with a much more rigid structure than antibodies, but that are distinct from each other by the set of amino acids present on the binding surface. The two teams have isolated, sequenced, and mass produced nine proteins with strong affinity for gold and more specifically for (111) crystal planes. When added to a gold nanoparticle growth solution, these proteins govern the nanocrystal shape (decahedra, icosahedra, plates) and size (50-500 nm) but more importantly the faceting resulting in more than 85% exclusively Au(111)-faceted nanocrystals. Importantly, the protein shell spontaneously assembled on the nanocrystal facets is exploited to drive protein-mediated colloidal self-assembly and on-surface enzymatic catalysis.

These results, that have been published in Nanoscale (Royal Society of Chemistry), offer a generic and designable tool for producing nanocrystals with determined faceting, superior biocompatibility and versatile biofunctionalization towards plasmon-based devices and (bio)molecular sensors.

Reference : Directed evolution of artificial repeat proteins as habit modifiers for the morphosynthesis of (111)-terminated gold nanocrystals
J. Prasad, S. Viollet, K. L. Gurunatha, A. Urvoas, A. C. Fournier, M. Valerio-Lepiniec, C. Marcelot, B. Baris, P. Minard and E. Dujardin
Nanoscale - DOI : 10.1039/C9NR04497C

Contact :
Philippe Minard (I2BC)
Erik Dujardin (CEMES)

par Communication - publié le