Structure of photosynthetic glyceraldehyde-3-­phosphate dehydrogenase (isoform A₄) from Arabidopsis thaliana in complex with NAD

The crystal structure of the A₄ isoform of photosynthetic glyceraldehyde-3-­phosphate dehydrogenase (GAPDH) from Arabidopsis thaliana, expressed in recombinant form and complexed with NAD, is reported. The crystals, which were grown in 2.4 M ammonium sulfate and 0.1 M sodium citrate, belonged to space group I222. The asymmetric unit includes ten subunits, i.e. two independent tetramers plus a dimer that generates a third tetramer by a crystallographic symmetry operation. The crystal structure was solved by molecular replacement and refined to an R factor of 23.7% and an R_free factor of 28.9% at 2.6 Å resolution. In the final model, each subunit binds one NAD⁺ molecule and two sulfates, which occupy the P_s and the P_i anion-binding sites. Detailed knowledge of this structure is instrumental for structural investigation of supramolecular complexes of A₄-GAPDH, phosphoribulokinase and CP12, which are involved in the regulation of photosynthesis in the model plant A. thaliana.