Tertiary and quarternary structure of GdPDC. A) A cartoon representation of GdPDC structure monomer (left) and dimer (right) showing the PYR–domain in red, PP-domain in blue and the R-domain in green. ThDP and Mg2+ are shown as space fill models. B) 2Fo-Fc electron density map (blue, contoured at 2.0 σ) for ThDP. The lack of electron density for the C2 position of the thiazole ring may indicate the loss of this atom.