Non-equilibrium nature of two-dimensional isotropic and nematic coexistence

Transcription

1 Non-equilibrium nature of two-dimensional isotropic and nematic coexistence in amyloid fibrils at liquid interfaces Supplementary Information Sophia Jordens 1, Lucio Isa 2, Ivan Usov 1, and Raffaele Mezzenga 1 * 1 ETH Zurich, Laboratory of Food & Soft Materials, Schmelzbergstrasse 9, 8092 Zurich, Switzerland 2 ETH Zurich, Laboratory for Surface Science & Technology, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland *raffaele.mezzenga@hest.ethz.ch

2 Supplementary Figure S1. AFM (a) height and (b) phase images of the air-water interfacial fibril layer at adsorption time t = 10 min with initial bulk concentration c init = 0.001% w/w. The slightly uneven structure of the background is due to the presence of non-fibrillar material. Both scale bars corresponds to 500 nm.

3 Supplementary Figure S2. Large scale AFM image of the air-water interfacial fibril layer at adsorption time t = 30 min with initial bulk concentration c init = 0.005% w/w. The scale bar represents 1 μm.

4 <x 2 >, <y 2 >, <x 2 + y 2 > [ m 2 ] E time [s] Supplementary Figure S3. Mean square displacement x 2 + y 2 versus time for tracer particles at the MCT-aqueous c init = 0.001% w/w fibril solution interface after 6 minutes adsorption time. The total msd (filled squares) was decomposed into the component in the main direction (x, open triangles) and the transverse direction of tracer motion (y, open circles). The fit with slope ± indicates twodimensional diffusive motion.

5 Supplementary Figure S4. Mean square displacement x 2 + y 2 vs time for tracer particles at an MCTaqueous fibril suspension interface with initial bulk concentration c init = 0.005% w/w after 8 (black), 24 (dark grey), and 37 minutes (light grey) adsorption time. Representative traces are shown for short (top) and long (bottom) times, with both scale bars corresponding to 200 nm. The straight line with slope 1 indicates two-dimensional diffusive motion.

6 Supplementary Note 1 Passive probe particle tracking. At low interfacial densities, equivalent to short t and / or low c init, the interface is purely viscous (tracers move diffusively, mean square displacement (msd) x 2 + y 2 ~ t, see Supplementary Fig. S3) and all tracers exhibit isotropic motion ( x 2 = y 2 ). In this regime, the in-plane interface structure can reach equilibrium and tracers are able to sample an isotropic environment. The msds of tracer particles as a function of time change from diffusive to sub-diffusive as fibrils adsorb at the interface from the bulk and the interfacial fibril density increases. Initially, tracers at the interface undergo Brownian motion in 2D. At later stages of the experiment (~ 20 minutes in the case of adsorption from c init = 0.005% w/w), some tracers develop highly anisotropic motion, while others become caged in the fibril network around them, see Supplementary Figure S4. The overall msd becomes sub-diffusive and is indicative of viscoelasticity the interface jams. As discussed in Isa et al. 8, this anisotropic motion is an indication of fibrillar alignment in 2D whereas isotropic sub-diffusive motion is a result of these particular tracers sampling interfacial areas with randomly oriented fibrils. It is noteworthy that, when starting from rather low c init, tracer anisotropy occurs before the interface becomes viscoelastic 8. The information on local structural properties of the interface, hidden in the overall msd(t) plot, can be extracted by creating a map of the degree of individual tracer motion anisotropy, as shown in Figure 1a of the main manuscript. If the rate of formation of nematic islands is low, i.e. by adsorption from low concentration fibril solutions, tracer particles are more likely to be dragged along with the advancing front of aligned regions to minimize distortion 45, outlining the contour of nematic domains. Tracers can, on the other hand, remain trapped inside nematic domains if these are formed at sufficiently high rates from high bulk fibril concentrations as shown by Isa et al. 8. Supplementary Note 2 Peptide layer. We consistently observed the presence of a layer of non-fibrillar material putatively peptides at the interface (Supplementary Fig. S3). The virtually constant height of this film shows that the interfacial structure is not disrupted by the transfer. Neither longer dialysis, additional filtration, nor any other techniques used were able to prevent the formation of this layer. There are two possible explanations for this phenomenon. Either β-lactoglobulin fibrils immediately partially disassemble upon adsorption to an interface, or, the fibrils are at thermodynamic equilibrium with peptides, which are their

7 46, 47 constituent building blocks. This has been proposed in a few reports for Aβ and SH3 domain fibrils but not yet for β-lactoglobulin. Supplementary References 45. West, J. L. et al. Drag on particles in a nematic suspension by a moving nematic-isotropic interface. Phys. Rev. E 66, (2002). 46. O Nuallain, B., Shivaprasad, S., Kheterpal, I., Wetzel, R. Thermodynamics of Aβ(1-40) amyloid fibril elongation. Biochemistry 44, (2005). 47. Carulla, N. et al. Molecular recycling within amyloid fibrils. Nature 436, (2005).