title: Exploring the stability limits of actin and its suprastructures.
abstract: Actin is the main component of the microfilament system in eukaryotic cells and can be found in distinct morphological states. Global (G)-actin is able to assemble into highly organized, supramolecular cellular structures known as filamentous (F)-actin and bundled (B)-actin. To evaluate the structure and stability of G-, F-, and B-actin over a wide range of temperatures and pressures, we used Fourier transform infrared spectroscopy in combination with differential scanning and pressure perturbation calorimetry, small-angle x-ray scattering, laser confocal scanning microscopy, and transmission electron microscopy. Our analysis was designed to provide new (to our knowledge) insights into the stabilizing forces of actin self-assembly and to reveal the stability of the actin polymorphs, including in conditions encountered in extreme environments. In addition, we sought to explain the limited pressure stability of actin self-assembly observed in vivo. G-actin is not only the least temperature-stable but also the least pressure-stable actin species. Under abyssal conditions, where temperatures as low as 1-4°C and pressures up to 1 kbar are reached, G-actin is hardly stable. However, the supramolecular assemblies of actin are stable enough to withstand the extreme conditions usually encountered on Earth. Beyond ∼3-4 kbar, filamentous structures disassemble, and beyond ∼4 kbar, complete dissociation of F-actin structures is observed. Between ∼1 and 2 kbar, some disordering of actin assemblies commences, in agreement with in vivo observations. The limited pressure stability of the monomeric building block seems to be responsible for the suppression of actin assembly in the kbar pressure range.
authors.affiliation: Physical Chemistry I-Biophysical Chemistry, Department of Chemistry and Chemical Biology, TU Dortmund University, Dortmund, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Rosin
authors.affiliation: Physical Chemistry I-Biophysical Chemistry, Department of Chemistry and Chemical Biology, TU Dortmund University, Dortmund, Germany.
authors.forename: Mirko
authors.initials: M
authors.lastname: Erlkamp
authors.affiliation: Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
authors.forename: Julian von der
authors.initials: JV
authors.lastname: Ecken
authors.affiliation: Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Raunser
authors.affiliation: Physical Chemistry I-Biophysical Chemistry, Department of Chemistry and Chemical Biology, TU Dortmund University, Dortmund, Germany. Electronic address: roland.winter@tu-dortmund.de.
authors.forename: Roland
authors.initials: R
authors.lastname: Winter
mesh_terms: D000199:Actins / Q000737:chemistry*; D000595:Amino Acid Sequence; D008969:Molecular Sequence Data; D011489:Protein Denaturation; D055550:Protein Stability; D044366:Transition Temperature
chemical_list: D000199:Actins