Hello, I have a question about comparing anisotropic displacement parameters for a series of 6 mutant and a wt structure with diffraction from 1.2-1.5 Å. The space group and unit cell for the series is the same, and most xtals were obtained by seeding from a hit for one mutant. There are two mols in the ASU which form an NCS dimer and the mutations alter dimer contacts in the xtals, and also alter dimer Kd measured by AUC. However, some of the mutants do not measurably dimerize in solution, but still form dimers in the xtal lattice.
When I study the individual anisotropic displacement parameters (derived from decomposition of the TLS tensors using TLSANL) of the structural elements making up the dimer interface, the magnitude and anisotropy of the displacements are increased for the complexes that form weaker dimers or dont dimerize at all in solution. I interpret this as a reflection of the weakened or non-existent interaction between monomers observed in solution for these complexes. But the question is how valid is it really to compare across-crystals? The total anisotropic displacement parameter U(tot) = U(cryst) + U(int) + U(atom) +U(TLS) so presumably cross-crystal differences are being accounted for by the single anisotropic parameter applied to the unit cell in Ucryst which would suggest that drawing such conclusions across crystals may be reasonable. Any insights or thoughts would be greatly appreciated. Thanks very much, Charu
