Structure of the MAT(α2)4(βV2)2 complex. (a) Crystallographic structure of the MAT(α2)4(βV2)2 complex. Two MATα2 monomers with visible gating loops are coloured in slate whereas the other two MATα2 monomers are coloured in red. MATβV2 is coloured in green with the first visible residues at its N-terminal in orange. The reaction product (SAMe) is represented by spheres. (b) SAXS of the MAT(α2)4(βV2)2 complex, the experimental spectrum (blue) is shown with a simulated fit (red) obtained from the crystal structure (qmax = 0.3 Å−1) (χ2 = 3.2). The radius of gyration, Rg = 50.1 ± 0.05 Å, was estimated from the low-angle scattering region by a Guinier plot. The distance distribution function, P(r), with maximum linear dimension Dmax = 187 Å. We interpret the higher χ2 value as arising in part from the flexibility of the interaction and the missing residues at the N-terminus of both MATβ subunits in the crystal structure. This is supported when SAXS data of the MATα2βV1Δ16 mutant (slightly better quality data, data not shown) are used with the model from the crystal structure (χ2 = 1.7). (c) The ab initio shape reconstruction of MAT(α2)4(βV2)2 by DAMMIN using P1 symmetry, showing a good agreement between the predicted molecular shape (light green mesh) and the crystal structure (Rg = 50.7) (cartoon), after alignment by SUPCOMB (Kozin & Svergun, 2001) (NSD = 0.93).