English: The assembled heterotrimer of protein phosphatase 2A. The regulatory subunit A, consisting of 15 HEAT repeats, is shown in rainbow color with the N-terminus in blue at bottom and the C-terminus in red at top. (Compare File:Alpha solenoid pp2a 2iae with single repeat center.png.) The regulatory subunit B, consisting of irregular pseudo-HEAT repeats, is shown in light blue. The catalytic subunit C is shown in tan. (All from PDB ID 2IAE.) Superposed is the unbound form of the regulatory subunit A in gray (from PDB ID 1B3U), illustrating the flexibility of this alpha solenoid protein. Conformational changes in HEAT repeat 11 result in flexing the C-terminal end of the protein to accommodate binding of the catalytic subunit.

PDB 2IAE: Cho US, Xu W. Crystal structure of a protein phosphatase 2A heterotrimeric holoenzyme. (2007). Nature 445, 53-57. DOI 10.1038/nature05351

PDB 1B3U:

Groves MR, Hanlon N, Turowski P, Hemmings BA, Barford D. The structure of the protein phosphatase 2A PR65/A subunit reveals the conformation of its 15 tandemly repeated HEAT motifs. Cell. 1999 Jan 8;96(1):99-110. DOI 10.1016/S0092-8674(00)80963-0