Intermolecular reorganisation of single-component condensates during ageing promotes multiphase architectures.

Intracellular proteins can undergo phase separation to form liquid-like biomolecular condensates with a multitude of functional roles. Liquid condensates can, however, further age and progressively rigidify. In addition to single-phase systems, multiphase condensates are increasingly identified commonly within multi-component systems, where the different molecular components present sufficient physicochemical diversity to sustain separate phases. Here, we develop a multiscale modeling approach that predicts conditions under which multiphase architectures can arise also within single-component protein condensates. Such single-component condensates are initially homogeneous but become heterogeneous over time due to the gradual enhancement of interprotein interactions. We find that such enhancement could originate, for instance, from intermolecular disorder-to-order transitions within low-complexity aromatic-rich kinked segments in the prion-like domain of FUS. Our model reveals that as increasing numbers of molecules undergo a disorder-to-order transition over time, single-component protein condensates convert into either gel-core/liquid-shell or liquid-core/gel-shell multiphase structures, depending on the relative surface tension of the liquid and gel phases. Despite being formed by proteins that are chemically-identical, the different liquid and gel phases present diverse surface tensions due to their fundamentally different molecular organization. Our study highlights the regulatory role of prion-like domains in tuning condensate behavior and, more generally, suggests a new route by which multilayered compartments or hierarchically organized condensate structures can emerge.

Possible Role of Non-Stationarity of Magnetohydrodynamic Turbulence in Understanding of Geomagnetic Excursions

The natural simplifying assumptions often put forward in the theoretical investigations of the magnetohydrodynamic turbulence are that the turbulent flow is statistically isotropic, homogeneous and stationary. Of course, the natural turbulence in the planetary interiors, such as the liquid core of the Earth is neither, which has important consequences for the dynamics of the planetary magnetic fields generated via the hydromagnetic dynamo mechanism operating in the interiors of the planets. Here we concentrate on the relaxation of the assumption of statistical stationarity of the turbulent flow and study the effect of turbulent wave fields in the Earth’s core, which induces non-stationarity, on the turbulent resistivity in the non-reflectionally symmetric flow and the geodynamo effect. It is shown that the electromotive force, including the so-called α-effect and the turbulent magnetic diffusivity η¯, induced by non-stationary turbulence, evolves slowly in time. However, the turbulent α¯ coefficient, responsible for the dynamo action and η¯ evolve differently in time, thus creating periods of enhanced and suppressed turbulent diffusion and dynamo action somewhat independently. In particular, periods of enhanced α¯ may coincide with periods of suppressed diffusion, leading to a stable and strong field period. On the other hand, it is shown that when enhanced diffusion occurs simultaneously with suppression of the α-effect, this leads to a sharp drop in the intensity of the large-scale field, corresponding to a geomagnetic excursion.