Single-Molecule Study of Peptide Gel Dynamics Reveals States of Prestress

Abstract

De novo peptide surfactant (I 3 K) gels provide an ideal system to study the complex dynamics of lightly crosslinked semiflexible fibers because of their large contour lengths, simple chemistry, and slow dynamics. We used single-molecule fluorescence microscopy to record individual fibers and Fourier decomposition of the fiber dynamics to separate thermal contributions to the persistence length from compressive states of prestress (SPS). Our results show that SPS in the network depend strongly on peptide concentration, buffer, and pH and that the fibril energies in SPS follow a Levy distribution. The presence of SPS in the network imply that collective states of self-stress are also present. Therefore, semiflexible polymer gels need to be considered as complex load-bearing structures and the mean field models for polymer gel elasticity and dynamics often applied to them will not be fully representative of the behavior at the nanoscale. We quantify the impact of cross-links on reptation tube dynamics, which provides a second population of tube fluctuations in addition to those expected for uncross-linked entangled solutions.

Network Organisation and the Dynamics of Tubules in the Endoplasmic Reticulum

“…The blue tubule in Figure 4A has no sustained curvature, as shown by the mean mode amplitudes of zero in Figure 4E. Contact sites between the ER and other cellular structures may facilitate these curved tubule configurations, also known as states of prestress (36,37).…”

“…The Fourier modes of each tubule were then calculated using the spatial co-ordinates determined using the modified version of FiberApp. Several custom Matlab scripts based on previous work (36,37) were written to calculate and analyse the Fourier mode amplitudes.…”

“…In order to study the curvature dynamics of ER tubules, tubule contours were decomposed into Fourier modes (37,49). This led to a more detailed description of individual tubule dynamics.…”

“…(10), the persistence length found was 5.6 ± 0.7 m (n = 83 tubules, mean ± SEM, see Figure 4F). Wavevector values of less than 3 m −1 were not included in the fit, as these modes are suppressed due to the finite separation of cross-linkers (MCS and interactions with microtubules in this model) along the fibre (29,37). The deviation from the expected −2 dependence indicates the presence of active motors and organelles (29).…”

Active Modulation of States of Prestress in Self-Assembled Short Peptide Gels

“…We then applied a naive Bayesian mixture model to identify the population of fibrils under stress in the networks. 17 Thus, the modulation of stresses in the peptide networks provides an excellent opportunity to control the physical properties of these materials. More generally, the use of stresses to precondition biopolymer networks has already been demonstrated to modulate the network load-bearing capabilities on the macroscale, e.g., with collagen.…”