title: The impact of solubility and electrostatics on fibril formation by the H3 and H4 histones.
abstract: The goal of this study was to examine fibril formation by the heterodimeric eukaryotic histones (H2A-H2B and H3-H4) and homodimeric archaeal histones (hMfB and hPyA1). The histone fold dimerization motif is an obligatorily domain-swapped structure comprised of two fused helix:β-loop:helix motifs. Domain swapping has been proposed as a mechanism for the evolution of protein oligomers as well as a means to form precursors in the formation of amyloid-like fibrils. Despite sharing a common fold, the eukaryotic histones of the core nucleosome and archaeal histones fold by kinetic mechanisms of differing complexity with transient population of partially folded monomeric and/or dimeric species. No relationship was apparent between fibrillation propensity and equilibrium stability or population of kinetic intermediates. Only H3 and H4, as isolated monomers and as a heterodimer, readily formed fibrils at room temperature, and this propensity correlates with the significantly lower solubility of these polypeptides. The fibrils were characterized by ThT fluorescence, FTIR, and far-UV CD spectroscopies and electron microscopy. The helical histone fold comprises the protease-resistant core of the fibrils, with little or no protease protection of the poorly structured N-terminal tails. The highly charged tails inhibit fibrillation through electrostatic repulsion. Kinetic studies indicate that H3 and H4 form a co-fibril, with simultaneous incorporation of both histones. The potential impact of H3 and H4 fibrillation on the cytotoxicity of extracellular histones and α-synuclein-mediated neurotoxicity and fibrillation is considered.
authors.affiliation: School of Molecular Biosciences, Washington State University, Pullman, Washington 99164-7520, USA.
authors.forename: Traci B
authors.initials: TB
authors.lastname: Topping
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Gloss
mesh_terms: D000682:Amyloid / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism*; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D017510:Protein Folding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012995:Solubility; D055672:Static Electricity; D014982:Xenopus laevis
chemical_list: D000682:Amyloid; D019843:Archaeal Proteins; D006657:Histones