title: Complex energy landscape of a giant repeat protein.
abstract: 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.
authors.affiliation: MRC Cancer Cell Unit, Hutchison/MRC Research Centre, Hills Road, Cambridge CB2 0XZ, UK; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK.
authors.forename: Maksym
authors.initials: M
authors.lastname: Tsytlonok
authors.forename: Patricio O
authors.initials: PO
authors.lastname: Craig
authors.forename: Elin
authors.initials: E
authors.lastname: Sivertsson
authors.forename: David
authors.initials: D
authors.lastname: Serquera
authors.forename: Sarah
authors.initials: S
authors.lastname: Perrett
authors.forename: Robert B
authors.initials: RB
authors.lastname: Best
authors.forename: Peter G
authors.initials: PG
authors.lastname: Wolynes
authors.forename: Laura S
authors.initials: LS
authors.lastname: Itzhaki
mesh_terms: D019943:Amino Acid Substitution; D020134:Catalytic Domain; D006801:Humans; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D011485:Protein Binding; D011489:Protein Denaturation; D054648:Protein Phosphatase 2 / Q000737:chemistry* / Q000235:genetics; D058849:Protein Refolding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: C517191:PPP2R1A protein, human; D054648:Protein Phosphatase 2