Exceptionally stable, redox-active supramolecular protein assemblies with emergent properties

Abstract

The designed assembly of proteins into well-defined supramolecular architectures not only tests our understanding of proteinprotein interactions, but it also provides an opportunity to tailor materials with new physical and chemical properties. Previously, we described that RIDC3, a designed variant of the monomeric electron transfer protein cytochrome cb 562 , could self-assemble through Zn 2+ coordination into uniform 1D nanotubes or 2D arrays with crystalline order. Here we show that these 1D and 2D RIDC3 assemblies display very high chemical stabilities owing to their metal-mediated frameworks, maintaining their structural order in ≥90% (vol/vol) of several polar organic solvents including tetrahydrofuran (THF) and isopropanol (iPrOH). In contrast, the unassembled RIDC3 monomers denature in ∼30% THF and 50% iPrOH, indicating that metal-mediated self-assembly also leads to considerable stabilization of the individual building blocks. The 1D and 2D RIDC3 assemblies are highly thermostable as well, remaining intact at up to ∼70°C and ∼90°C, respectively. The 1D nanotubes cleanly convert into the 2D arrays on heating above 70°C, a rare example of a thermal crystalline-to-crystalline conversion in a biomolecular assembly. Finally, we demonstrate that the Zn-directed RIDC3 assemblies can be used to spatiotemporally control the templated growth of small Pt 0 nanocrystals. This emergent function is enabled by and absolutely dependent on both the supramolecular assembly of RIDC3 molecules (to form a periodically organized structural template) and their innate redox activities (to direct Pt 2+ reduction).protein self-assembly | supramolecular coordination chemistry | nanomaterials | biomaterials | inorganic nanoparticles T he enormous structural and chemical diversity of proteins makes them highly attractive building blocks for functional materials. Supramolecular protein assemblies constitute the major components of cellular machinery, and many of them [e.g., 0D ferritin (1), 1D silicatein filaments (2, 3), 2D S-layers (4)] have also found a number of applications in nano-and biotechnology (2, 4, 5). Such protein assemblies are typically highly ordered, yet they possess dynamic structures that respond to external stimuli (6). Distinctively, protein assemblies are innately functional: the individual building blocks of these assemblies often perform specific chemical functions. For instance, the monomeric components of silicatein filaments or ferritin cages each have catalytic sites that process the precursors (SiO 2 or Fe 2+ ) for the downstream biomineralization processes (1, 3). On self-assembly, these individual components can be significantly stabilized (allowing them to withstand the extracellular environment and perform their functions) (7), and their chemical function takes on an entirely different context within the supramolecular architecture (acting as the template for biomineralization in the cases of silicatein and ferritin). Thus, they display emergent properties, both structurally and functionally.Such a...

Supercharging enables organized assembly of synthetic biomolecules

“…Control SuPrA protomers containing entirely Ceru+32, entirely GFP-17, or an octamer of Ceru+32 juxtaposed with an octamer of GFP-17 were unstable at all NaCl concentrations, consistent with the experimental observations ( Supplementary Fig. 12, 13) Finer-grained structural modeling (i.e., of hydrophobic effects and counterion release) must await specific structural and physical details that should become manifest with further imaging (i.e., cryo-EM) experiments that better determine the precise symmetric arrangement of monomers.While previous studies have shown that it is possible to design synthetic protein oligomers either by modifying extant structures [13][14][15][16] or de novo, [8][9][10][11][12] we now show that it may be possible to induce the formation of novel quaternary structures through the simple expedient of supercharging. In so doing, we demonstrate that precise molecular configurations can be obtained by focusing on the driving forces for assembly (charge:charge interactions) rather than the details of the interface.…”

“…While previous studies have shown that it is possible to design synthetic protein oligomers either by modifying extant structures [13][14][15][16] or de novo, [8][9][10][11][12] we now show that it may be possible to induce the formation of novel quaternary structures through the simple expedient of supercharging. In so doing, we demonstrate that precise molecular configurations can be obtained by focusing on the driving forces for assembly (charge:charge interactions) rather than the details of the interface.…”

“…[1][2][3][4][5][6][7] Repeated, symmetric interactions between molecular building blocks enable the formation of complex, defined, assemblies from a small total number of components as well as dynamic propagation of conformational change. [3][4][5][6][7][8] However, while de novo engineering of artificial symmetrical biomolecular complexes has begun to be explored, [9][10][11][12][13][14][15] these efforts generally rely upon precise design of molecular interfaces. 16,17 In contrast, studies of simple synthetic colloids suggests that higher order structures can be derived based solely on packing and energetic and considerations.…”

Precise protein assembly of array structures

“…Interestingly, the 3D protein arrays eventually formed a single crystal, the atomic structure of which was resolved by X-ray crystallography, presenting solid evidence on the mechanism. Moreover, the 1D protein nanotubes were found to completely convert to the thermodynamically more stable 2D protein arrays after heating, showing the valuable character of stimuli response of protein assemblies 48 . Finally, rhodamine was incorporated at the surface of cb562.…”

Protein nanorings organized by poly(styrene-block-ethylene oxide) self-assembled thin films

“…24 The main challenge facing the field of protein nanotechnology is the ability to control proteinprotein interactions to build up higher order structures, and in particular to order these structures. Previous work on creating protein assemblies has been largely centered around amyloid fibers [25][26][27][28][29] but has recently also involved native protein structures [30][31][32] with ring shaped proteins emerging as a commonly used self-assembling feature. [33][34][35][36][37] Recent work has established methods to post functionalize assembled structures, 38,39 an important step towards applications based on protein nanostructures.…”