Fig. 3.

Conformation of α-catenin by itself and as part of the ^dA^hB^hE complex. (A) SEC-SAXS data of the α-catenin monomer alone in solution (black dots). Data are taken from ref. 38. SANS data of the ^dA^hB^hE complex, c = 3.7 mg/mL, in 42% D₂O (red squares) at the contrast-matching point of ^hB^hE, which only reveals the conformation of ^dα-catenin in the complex. Red lines are fits to the experimental scattering data for generating P(r). SI Appendix, Fig. S4 A and B shows Guinier plots and Kratky plots. (B) P(r) of the α-catenin monomer in solution (black) and of ^dα-catenin in the ^dA^hB^hE complex (red) generated from the scattering data in A. (C) The 3D shapes of the α-catenin monomer generated from SEC-SAXS data using the program DAMMIF/DAMMIN (73). (D) The 3D shape of ^dα-catenin within the ^dA^hB^hE complex generated from contrast-matching SANS data in 42% D₂O using the program Gasbor (68). Docked into the 3D shapes are the α-catenin structures in solution and in the ^dA^hB^hE complex, which were generated by Monte Carlo simulations using the program SASSIE (43). (E and F) R_g distribution (E) and D_max distribution (F) from EOM analysis (41, 42) of the SAXS and SANS data of the α-catenin monomer in solution (black) and of ^dα-catenin as a part of the ^dA^hB^hE complex (red). For the α-catenin monomer, R_flex = 75.3% (pool 84.5%) and R_σ = 0.68. For ^dα-catenin within the ^dA^hB^hE complex, R_flex = 72.9%, Pool 85.4%, and R_σ = 0.62. These values suggest that α-catenin is a flexible molecule. (G) Flexible structural models of ^dα-catenin in the ^dA^hB^hE complex obtained from Monte Carlo simulations show that the M domain and the ABD can adopt multiple configurations. The simulations were performed using the SANS data of ^dA^hB^hE in 42% D₂O buffer as constraints. SI Appendix, Fig. S4 C and D shows quality of fit.