Complex energy landscape of a giant repeat protein

Structure. 2013 Nov 5;21(11):1954-65. doi: 10.1016/j.str.2013.08.028. Epub 2013 Oct 10.


Here, we reveal a remarkable complexity in the unfolding of giant HEAT-repeat protein PR65/A, a molecular adaptor for the heterotrimeric PP2A phosphatases. The repeat array ruptures at multiple sites, leading to intermediate states with noncontiguous folded subdomains. There is a dominant sequence of unfolding, which reflects a nonuniform stability distribution across the repeat array and can be rationalized by theoretical models accounting for heterogeneous contact density in the folded structure. Unfolding of certain intermediates is, however, competitive, leading to parallel unfolding pathways. The low-stability, central repeats sample unfolded conformations under physiological conditions, suggesting how folding directs function: certain regions present rigid motifs for molecular recognition, whereas others have the flexibility with which to broaden the search area, as in the fly-casting mechanism. Partial unfolding of PR65/A also impacts catalysis by altering the proximity of bound catalytic subunit and substrate. Thus, the repeat array orchestrates the assembly and activity of PP2A.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Catalytic Domain
  • Humans
  • Kinetics
  • Molecular Dynamics Simulation
  • Protein Binding
  • Protein Denaturation
  • Protein Phosphatase 2 / chemistry*
  • Protein Phosphatase 2 / genetics
  • Protein Refolding
  • Protein Stability
  • Protein Structure, Secondary
  • Thermodynamics


  • PPP2R1A protein, human
  • Protein Phosphatase 2