Directed evolution of artificial repeat proteins as habit modifiers for the morphosynthesis of (111)-terminated gold nanocrystals

Anisotropic Gold Nanomaterial Synthesis Using Peptide Facet Specificity and Timed Intervention

Thin metal particles with two-dimensional (2D) symmetry are attractive for multiple applications but are difficult to synthesize in a reproducible manner. Although molecules that selectively adsorb to facets have been used to control nanoparticle shape, there is still limited research into the temporal control of growth processes to control these structural outcomes. Moreover, much of the current research into the growth of thin 2D particles lacks mechanistic details. In this work, we study why the substitution of isoleucine for methionine in a gold-binding peptide (Z2, RMRMKMK) results in an increase in gold nanoparticle anisotropy. Nanoplatelet growth in the presence of Z2M246I (RIRIKIK) is characterized using in situ small-angle X-ray scattering (SAXS) and UV-vis spectroscopy. Fitting time-resolved SAXS profiles reveal that 10 nm-thick particles with 2D symmetry are formed within the first few minutes of the reaction. Next, through a combination of electron diffraction and molecular dynamics simulations, we show that substitution of methionine for isoleucine increases the (111) facet selectivity in Z2M246I, and we conclude that this is key to the growth of nanoplatelets. However, the potential application of nanoplatelets formed using Z2M246I is limited due to their uncontrolled lateral growth, aggregation, and rapid sedimentation. Therefore, we use a liquid-handling robot to perform temporally controlled synthesis and dynamic intervention through the addition of Z2 to nanoplatelets grown in the presence of Z2M246I at different times. UV-vis spectroscopy, dynamic light scattering, and electron microscopy show that dynamic intervention results in control over the mean size and stability of plate-like particles. Finally, we use in situ UV-vis spectroscopy to study plate-like particle growth at different times of intervention. Our results demonstrate that both the selectivity and magnitude of binding free energy toward lattices are important for controlling nanoparticle growth pathways.

Macromolecular interactions in vitro, comparing classical and novel approaches

Biophysical quantification of protein interactions is central to unveil the molecular mechanisms of cellular processes. Researchers can choose from a wide panel of biophysical methods that quantify molecular interactions in different ways, including both classical and more novel techniques. We report the outcome of an ARBRE-MOBIEU training school held in June 2019 in Gif-sur-Yvette, France ( https://mosbio.sciencesconf.org/ ). Twenty European students benefited from a week's training with theoretical and practical sessions in six complementary approaches: (1) analytical ultracentrifugation with or without a fluorescence detector system (AUC-FDS), (2) isothermal titration calorimetry (ITC), (3) size exclusion chromatography coupled to multi-angle light scattering (SEC-MALS), (4) bio-layer interferometry (BLI), (5) microscale thermophoresis (MST) and, (6) switchSENSE. They implemented all these methods on two examples of macromolecular interactions with nanomolar affinity: first, a protein-protein interaction between an artificial alphaRep binder, and its target protein, also an alphaRep; second, a protein-DNA interaction between a DNA repair complex, Ku70/Ku80 (hereafter called Ku), and its cognate DNA ligand. We report the approaches used to analyze the two systems under study and thereby showcase application of each of the six techniques. The workshop provided students with improved understanding of the advantages and limitations of different methods, enabling future choices concerning approaches that are most relevant or informative for specific kinds of sample and interaction.