Interplay between liquid crystalline and isotropic gels in self-assembled neurofilament networks.
Neurofilaments (NFs) are a major constituent of nerve cell axons that assemble from three subunit proteins of low (NF-L), medium (NF-M), and high (NF-H) molecular weight into a 10 nm diameter rod with radiating sidearms to form a bottle-brush-like structure. Here, we reassemble NFs in vitro from varying weight ratios of the subunit proteins, purified from bovine spinal cord, to form homopolymers of NF-L or filaments composed of NF-L and NF-M (NF-LM), NF-L and NF-H (NF-LH), or all three subunits (NF-LMH). At high protein concentrations, NFs align to form a nematic liquid crystalline gel with a well-defined spacing determined with synchrotron small angle x-ray scattering. Near physiological conditions (86 mM monovalent salt and pH 6.8), NF-LM networks with a high NF-M grafting density favor nematic ordering whereas filaments composed of NF-LH transition to an isotropic gel at low protein concentrations as a function of increasing mole fraction of NF-H subunits. The interfilament distance decreases with NF-M grafting density, opposite the trend seen with NF-LH networks. This suggests a competition between the more attractive NF-M sidearms, forming a compact aligned nematic gel, and the repulsive NF-H sidearms, favoring a more expansive isotropic gel, at 86 mM monovalent salt. These interactions are highly salt dependent and the nematic gel phase is stabilized with increasing monovalent salt.
Jones
Jayna B
JB
Materials Department, University of California, Santa Barbara, California 93106, USA.
Safinya
Cyrus R
CR
D016880:Anisotropy; D005782:Gels / Q000737:chemistry*; D050866:Liquid Crystals / Q000737:chemistry*; D046912:Multiprotein Complexes / Q000737:chemistry; D016900:Neurofilament Proteins / Q000737:chemistry*; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
D005782:Gels; D046912:Multiprotein Complexes; D016900:Neurofilament Proteins