PR65, the HEAT-repeat scaffold of phosphatase PP2A, is an elastic connector that links force and catalysis.
PR65 is the two-layered (alpha-alpha solenoid) HEAT-repeat (Huntingtin, elongation factor 3, a subunit of protein phosphatase 2A, PI3 kinase target of rapamycin 1) scaffold of protein phosphatase PP2A. Molecular dynamics simulations predict that, at forces expected in living systems, PR65 undergoes (visco-)elastic deformations in response to pulling/pushing on its ends. At lower forces, smooth global flexural and torsional changes occur via even redistribution of stress along the hydrophobic core of the molecule. At intermediate forces, helix-helix separation along one layer ("fracturing") leads to global relaxation plus loss of contact in the other layer to unstack the affected units. Fracture sites are determined by unusual sequences in contiguous interhelix turns. Normal mode analysis of the heterotrimeric PP2A enzyme reveals that its ambient conformational fluctuations are dominated by elastic deformations of PR65, which introduce a mechanical linkage between the separately bound regulatory and catalytic subunits. PR65-dominated fluctuations of PP2A have the effect of opening and closing the enzyme's substrate binding/catalysis interface, as well as altering the positions of certain catalytic residues. These results suggest that substrate binding/catalysis are sensitive to mechanical force. Force could be imposed from the outside (e.g., in PP2A's response to spindle tension) or arise spontaneously (e.g., in PP2A's interaction with unstructured proteins such as Tau, a microtubule-associated Alzheimer's-implicated protein). The presented example supports the view that conformation and function of protein complexes can be modulated by mechanical energy inputs, as well as by chemical energy inputs from ligand binding. Given that helical-repeat proteins are involved in many cellular processes, the findings also encourage the view that mechanical forces may be of widespread importance.
Grinthal
Alison
A
Departments of Molecular and Cellular Biology, and Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
Adamovic
Ivana
I
Weiner
Beth
B
Karplus
Martin
M
Kleckner
Nancy
N
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002384:Catalysis; D018360:Crystallography, X-Ray; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D054648:Protein Phosphatase 2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013314:Stress, Mechanical; D013379:Substrate Specificity; D013816:Thermodynamics
C432785:PPP2R1B protein, human; D054648:Protein Phosphatase 2