An Unusual Hydrophobic Core Confers Extreme Flexibility to HEAT Repeat Proteins

Christian Kappel, Ulrich Zachariae, Nicole Doelker, Helmut Grubmueller

Research output: Contribution to journalArticlepeer-review

Abstract

Alpha-solenoid proteins are suggested to constitute highly flexible macromolecules, whose structural variability and large surface area is instrumental in many important protein-protein binding processes. By equilibrium and nonequilibrium molecular dynamics simulations, we show that importin-beta, an archetypical a-solenoid, displays unprecedentedly large and fully reversible elasticity. Our stretching molecular dynamics simulations reveal full elasticity over up to twofold end-to-end extensions compared to its bound state. Despite the absence of any long-range intramolecular contacts, the protein can return to its equilibrium structure to within 3 angstrom backbone RMSD after the release of mechanical stress. We find that this extreme degree of flexibility is based on an unusually flexible hydrophobic core that differs substantially from that of structurally similar but more rigid globular proteins. In that respect, the core of importin-beta resembles molten globules. The elastic behavior is dominated by nonpolar interactions between HEAT repeats, combined with conformational entropic effects. Our results suggest that alpha-solenoid structures such as importin-beta may bridge the molecular gap between completely structured and intrinsically disordered proteins.

Original languageEnglish
Pages (from-to)1596-1603
Number of pages8
JournalBiophysical Journal
Volume99
Issue number5
DOIs
Publication statusPublished - 8 Sep 2010

Keywords

  • MOLECULAR-DYNAMICS SIMULATIONS
  • PARTICLE MESH EWALD
  • IMPORTIN-BETA
  • SINGLE-MOLECULE
  • MOLTEN GLOBULE
  • POTENTIAL FUNCTIONS
  • FORCE SPECTROSCOPY
  • ELASTIC PROPERTIES
  • STRUCTURAL BASIS
  • ROP PROTEIN

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