Fig. 2. Molecular organization of the yeast NPC. Total amino acid (aa) volume fraction (A and D), volume fraction of hydrophobic segments (B and E), and electrostatic potential (C and F) for the native and homogeneous model sequences (Fig. 1). The plots show that homogenizing the amino acid sequence affects the electrostatic potential but not the density of amino acids or the density of hydrophobic amino acids.

The flow behavior of polymeric liquids can be traced back to the complex conformational dynamics of polymer molecules in shear flow, which poses a major challenge to theory and experiment alike due to the inherently large number of degrees of freedom. Here we directly determine the configurational dynamics of individual actin filaments with varying lengths in a well defined shear geometry by combining microscopy, microfluidics, and a semiautomated moving stage. This allows the identification of the microscopic mechanisms and the derivation of an analytical model for the dynamics of individual filaments based on the balance of drag, bending, and stochastic forces.

The properties of polymer layers end-grafted to the inner surface of nanopores connected to solvent reservoirs are studied theoretically as a function of solvent quality and pore geometry. Our systematic study reveals that nanoconfinement is affected by both pore radius and length and that the conformations of the polymer chains strongly depend on their grafting position along the nanopore and on the quality of the solvent. In poor solvent, polymer chains can collapse to the walls, form a compact plug in the pore, or self-assemble into domains of different shape due to microphase separation. The morphology of these domains (aggregates on pore walls or stacked micelles along the pore axis) is mainly determined by the relationship between chain length and pore radius. In other cases the number of aggregates depends on pore length. The presence of reservoirs decreases confinement at pore edges due to the changes in available volume and introduces new organization strategies not available for infinite nanochannels. In good solvent conditions, chains grafted at the pore entrances stretch out of the pore, relieving the internal osmotic pressure and increasing the entropy of the polymers. Our study also addresses the experimentally relevant case of end-grafted chains on the outer walls of the membrane surrounding the nanopore. The effect of these polymer chains on the organization within the nanopore depends on solvent quality. For good solvents the outer chains increase the confinement of the chains at the entrance of the pore; however, the effect does not result in new structures. For poor solvents the presence of the outer polymer layer may lead to changes in the morphology of the microphase-separated domains. Our results show the complex interplay between the different interactions in a confined environment and the need to develop theoretical and experimental tools for their study.

A unified Flory-type theory of dendron brushes, dendrimers, dendronized polymers, and forests yields scaling rules, state diagrams and information on the collapse transition. The theory also describes the corresponding brushes of linear chains: stars, bottle brushes, and planar brushes. It thus permits a detailed discussion of various tuning parameters and their effects for the different brush types. The discussion addresses the effects of solvent quality, grafting density, the persistence length, and branching functionality. The theory is formulated for the case of "identical monomers" assuming that spacer monomers, junctions, and ends are identical in shape and interactions.

Honeybee Apis mellifera swarms form clusters made solely of bees attached to each other, forming pendant structures on tree branches (1). These clusters can be hundreds of times the size of a single organism. How these structures are stably maintained under the influence of static gravity and dynamic stimuli (e.g. wind) is unknown. To address this, we created pendant conical clusters attached to a board that was shaken with varying amplitude, frequency and total duration. Our observations show that horizontally shaken clusters spread out to form wider, flatter cones, i.e. the cluster adapts to the dynamic loading conditions, but in a reversible manner -when the loading is removed, the cluster recovers its original shape, slowly. Measuring the response of a cluster to a sharp pendular excitation before and after it adapted shows that the flattened cones deform less and relax faster than the elongated ones, i.e. they are more stable mechanically. We use particle-based simulations of a passive assemblage to suggest a behavioral hypothesis that individual bees respond to local variations in strain. This behavioral response improves the collective stability of the cluster as a whole at the expense of increasing the average mechanical burden experienced by the individual. Simulations using this rule explain our observations of adaptation to horizontal shaking. The simulations also suggest that vertical shaking will not lead to significant differential strains and thus no adaptation. To test this, we shake the cluster vertically and find that indeed there is no response to this stimulus. Altogether, our results show how an active, functional super-organism structure can respond adaptively to dynamic mechanical loading by changing its morphology to achieve better load sharing.

Several biological mechanisms involve proteins or proteinaceous components that are intrinsically disordered. A case in point pertains to the nuclear pore complex (NPC), which regulates molecular transport between the nucleus and the cytoplasm. NPC functionality is dependent on unfolded domains rich in Phe-Gly (FG) repeats (i.e., FG-domains) that collectively act to promote or hinder cargo translocation. To a large extent, our understanding of FG-domain behavior is limited to in vitro investigations given the difficulty to resolve them directly in the NPC. Nevertheless, recent findings indicate a collective convergence towards rationalizing FG-domain function. This review aims to glean further insight into this fascinating problem by taking an objective look at the boundary conditions and contextual details underpinning FG-domain behavior in the NPC. Here, we treat the FG-domains as being commensurate with polymeric chains to address ambiguities such as for instance, how FG-domains tethered to the central channel of the NPC would behave differently as compared with their free-floating counterparts in solution. By bringing such fundamental questions to the fore, this review seeks to illuminate the importance of how such parameters can hold influence over the structure-function relation of intrinsically disordered proteins in the NPC and beyond.

During mating season, males of synchronous firefly species flash in unison within swarms of thousands of individuals. These strongly correlated collective displays have inspired numerous mathematical models to explain how global synchronous patterns emerge from local interactions. Yet, experimental data to validate these models remain sparse. To address this gap, we develop a method for three-dimensional tracking of firefly flashes, using a stereoscopic set-up of 360-degree cameras. We apply this method to record flashing displays of the North American synchronous species Photinus carolinus in its natural habitat as well as within controlled environments, and obtain the three-dimensional reconstruction of flash occurrences in the swarm. Our results show that even a small number of interacting males synchronize their flashes; however, periodic flash bursts only occur in groups larger than 15 males. Moreover, flash occurrences are correlated over several metres, indicating long-range interactions. While this suggests emergent collective behaviour and cooperation, we identify distinct individual trajectories that hint at additional competitive mechanisms. These reveal possible behavioural differentiation with early flashers being more mobile and flashing longer than late followers. Our experimental technique is inexpensive and easily implemented. It is extensible to tracking light communication in various firefly species and flight trajectories in other insect swarms.

We use molecular dynamics simulations in 2D to study multi-component systems in the limiting case where all the particles are different (APD). The particles are assumed to interact via Lennard-Jones potentials, with identical size parameters but their pair interaction parameters are generated at random from a uniform or from a peaked distribution. We analyze both the global and the local properties of these systems at temperatures above the freezing transition and find that APD fluids relax into a non-random state characterized by clustering of particles according to the values of their pair interaction parameters (particle-identity ordering).