The Physics of a “Smart” Bio‐Gel:
Direct Force Measurements on Self‐Assembled Neurofilament Hydrogels
Roy Beck, University of California Santa Barbara
Understanding biological systems poses huge theoretical and experimental challenges, attributable to their complexity, dynamics and many different elementary lengths scales involved in their interactions. These interactions scale from specific atomic‐scale covalent bonds through non‐specific long‐ranged electrostatics. The complexity of biological systems is multi‐scaled as well, as even a single cell is composed from many different, very complicated building‐blocks.
In this talk, I will introduce our recent results about neurofilament hydrogel, a very basic component of the neurons’ cytoskeleton. After we purify the three different subunit proteins from bovine spinal‐cord, they self‐assemble to form supra‐macromolecules filaments with a ‘bottlebrush’‐like geometry. When assembled at high density, these neurofilaments form a liquid‐crystalline hydrogels and serve as the matrix for the neuron’s long processes (axons and dendrites). They impart mechanical stability and act as structural scaffolds. Using synchrotron small angle x‐ray scattering under osmotic pressure coupled with various microscopy techniques, we directly measure the interfilament forces responsible for the mechanical properties of neurofilament hydrogels.
We show that the “smart” mechanical properties of neurofilament gels can be tuned by variation of the subunit proteins and osmotic pressure. Such modifications have been recorded for different stages in neuron development and correlated to numerous neurodegenerative iseases. Surprisingly, under certain conditions, such as critical pressure or specific subunit protein ratios, negatively net‐charged and sterically repulsing filaments show attractive interactions. We are able to explain these results via a competition between long‐ and short‐ranged interactions, with a key combination from electrostatic interaction between altering positive and negative charged residues along the neuroflament brushes.
