Crystallization and preliminary X-ray diffraction studies of Leu55Pro variant transthyretin

The amyloidogenic Leu55Pro variant of transthyretin has been expressed, purified and crystallized in space group C2. The cell constants are a = 149.99, b = 78.74, c = 98.95 A, beta = 100.5 degrees and the crystals diffract to 2.7 A resolution. There are eight monomers in the asymmetric unit giving a V(M) = 2.6 A(3) Da(-1) and 53% solvent content. In the wild-type protein, the crystals are orthorhombic with two monomers in the asymmetric unit. The wild-type protein is a tetramer composed of four identical subunits [Blake, Geisow, Oatley, Rerat & Rerat (1978). J. Mol. Biol. 121, 339-356.] and a molecular-replacement solution for the Leu55Pro variant was obtained using one monomer of the wild-type protein as a model. Rigid-body refinement of the eight monomers in the asymmetric unit and subsequent refinement using molecular dynamics were performed with X-PLOR, leading to a current R factor of 20.3% for all the data. The crystallographic packing of the molecules is different from the one presented by the wild-type protein, opening new perspectives for understanding how this protein aggregates to form amyloid fibrils.