title: Neurofilament networks: Salt-responsive hydrogels with sidearm-dependent phase behavior.
abstract: BACKGROUND
  Neurofilaments (NFs) - the neuron-specific intermediate filament proteins - are assembled into 10nm wide filaments in a tightly controlled ratio of three different monomer types: NF-Low (NF-L), NF-Medium (NF-M), and NF-High (NF-H). Previous work on reconstituted bovine NF hydrogels has shown the dependence of network properties, including filament alignment and spacing, on the subunit composition.
  
  
  METHODS
  We use polarized optical microscopy and SAXS to explore the full salt-dependent phase behavior of reconstituted bovine NF networks as a function of various binary and ternary subunit ratios.
  
  
  RESULTS
  We observe three salt-induced liquid crystalline phases: the liquid-ordered B(G) and N(G) phases, and the disordered I(G) phase. We note the emergent sidearm roles, particularly that of NF-H in driving the parallel to cross-filament transition, and the counter-role of NF-M in suppressing the I(G) phase.
  
  
  CONCLUSIONS
  In copolymers of NF-LH, NF-H shifts the I(G) to N(G) transition to nearer physiological salt concentrations, as compared to NF-M in copolymers of NF-LM. For ternary mixtures, the role of NF-H is modulated by the ratio of NF-M, where beneath 10wt.% NF-M, NF-H drives the transition to the disordered phase, and above which NF-H increases interfilament spacing.
  
  
  CONCLUSIONS
  Understanding the role of individual subunits in regulating the network structure will enable us to understand the mechanisms that drive the dysfunction of these networks, as observed in diseased conditions.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, United States. Electronic address: joanna.deek@tum.de.
authors.forename: Joanna
authors.initials: J
authors.lastname: Deek
authors.affiliation: Department of Physics, University of California, Santa Barbara, CA 93106, United States; Department of Materials, University of California, Santa Barbara, CA 93106, United States; Department of Molecular, Cellular, & Developmental Biology, University of California, Santa Barbara, CA 93106, United States. Electronic address: pjchung@physics.ucsb.edu.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chung
authors.affiliation: Department of Physics, University of California, Santa Barbara, CA 93106, United States; Department of Materials, University of California, Santa Barbara, CA 93106, United States; Department of Molecular, Cellular, & Developmental Biology, University of California, Santa Barbara, CA 93106, United States. Electronic address: cyrussafinya@ucsb.edu.
authors.forename: Cyrus R
authors.initials: CR
authors.lastname: Safinya
mesh_terms: D000818:Animals; D002021:Buffers; D002417:Cattle; D020100:Hydrogels; D007382:Intermediate Filaments / Q000737:chemistry*; D050866:Liquid Crystals; D008859:Microscopy, Polarization; D016900:Neurofilament Proteins / Q000737:chemistry*; D044367:Phase Transition; D011487:Protein Conformation; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: D002021:Buffers; D020100:Hydrogels; D016900:Neurofilament Proteins
keywords: Hydrogel; Liquid crystal; Network; Neurofilament; Salt-responsive; Sidearm-dependent