Effect of skull morphology on fox snow diving.

Certain fox species plunge-dive into snow to catch prey (e.g., rodents), a hunting mechanism called mousing. Red and arctic foxes can dive into snow at speeds ranging between 2 and 4 m/s. Such mousing behavior is facilitated by a slim, narrow facial structure. Here, we investigate how foxes dive into snow efficiently by studying the role of skull morphology on impact forces it experiences. In this study, we reproduce the mousing behavior in the lab using three-dimensional (3D) printed fox skulls dropped into fresh snow to quantify the dynamic force of impact. Impact force into snow is modeled using hydrodynamic added mass during the initial impact phase. This approach is based on two key facts: the added mass effect in granular media at high Reynolds numbers and the characteristics of snow as a granular medium. Our results show that the curvature of the snout plays a critical role in determining the impact force, with an inverse relationship. A sharper skull leads to a lower average impact force, which allows foxes to dive head-first into the snow with minimal tissue damage.

Effect of pseudorepeat rearrangement on alpha-synuclein misfolding, vesicle binding, and micelle binding.

The pathological and physiological hallmarks of the protein alpha-synuclein (aS) are its misfolding into cytotoxic aggregates and its binding to synaptic vesicles, respectively. Both events are mediated by seven 11-residue amphiphilic pseudorepeats and, most generally, involve a transition from intrinsically unstructured conformations to structured conformations. Based on aS interactions with aggregation-inhibiting small molecules, an aS variant termed shuffled alpha-synuclein (SaS), wherein the first six pseudorepeats had been rearranged, was introduced. Here, the effects of this rearrangement on misfolding, vesicle binding, and micelle binding are examined in reference to aS and beta-synuclein to study the sequence characteristics underlying these processes. Fibrillization correlates with the distinct clustering of residues with high beta-sheet propensities, while vesicle affinities depend on the mode of pseudorepeat interchange and loss. In the presence of micelles, the pseudorepeat region of SaS adopts an essentially continuous helix, whereas aS and beta-synuclein encounter a distinct helix break, indicating that a more homogeneous distribution of surfactant affinities in SaS prevented the formation of an extensive helix break in the micelle-bound state. By demonstrating the importance of the distribution of beta-sheet propensities and by revealing inhomogeneous aS surfactant affinities, the present study provides novel insights into two central themes of synuclein biology.