A significant population of selected models had a collapsed PR70 C-terminal region, suggestive of a folded region. Combining all the models from the different BilboMD runs and using a MES search to the experimental scattering data identified a group of three structures that gives a Chi free error of 0.92. The best ensemble with relative population percentages were 51% model derived with A subunit from 3dw8.pdb, 14% model derived from 1b37, and 35% from model derived from 4i5l. Notably, there is not a strong Fingolimod difference in the Chi fit between the MES search based on the BilboMD run with 3dw8 and the MES search with the mixed populations. Therefore, to obtain an complementary measure, we used a Volatility Ratio measure. VR is much less sensitive to Rg than Chi free and can be used as an orthogonal measure for how well the model matches the experimental data. The VR Similarity to the experimental data were 0.70 and 0.30 for the 3dw8 BilboMD run and for the mixed population MES, respectively. As 0 is expected for a perfect fit, the VR measure suggests that the MES with the mixed population better agrees with the experimental data. This MES analysis suggests that in the complex between the PR70 subunits, the heat 15 domains are still mobile and that the PR70 is flexible but may be partially folded. In this work we complement the very recent structure of PR70 in the heterotrimeric PP2A complex with a high resolution structure of the free PR70, as well as biochemical and low resolution data describing it’s interactions with the A-subunit in a dimeric complex. The structure of PR70 in the heterotrimer shows small but significant structural differences as compared with free PR70, supporting a degree of induced fit upon binding. Our biophysical studies emphasize a role for calcium in regulating the stability of PR70 and in the interaction to the A-subunit, in agreement with previous studies. Interesting, we show that PR70 and the A-subunit have high affinity to each other, opening for a scenario where this complex can be formed before the C-subunit is recruited to the heterotrimer. This is in contrast to the assembly of heterotrimers containing B- and B’-subunits where the initial formation of the core dimer is necessary. Although we failed in crystallizing the PR70-A-subunit heterodimer we used SAXS to study the complex in solution. Overall, the SAXS data of the A and PR70 subunit complex is consistent with the crystallographic structure of the entire complex including the catalytic domain. However, there are obvious differences, primarily with regard to the A subunit. SAXS data of the A subunit only were consistent with heat domains shifting relative to each other. The flexibility of the A-subunit has general functional relevance, as flexibility will both allow interaction with different Bsubunits and also affect off-rates from any one subunit. Importantly, the B-subunit in the case of PR70 does not significantly reduce the A-subunit flexibility.