Abstract
The crystal structure of NADP-dependent apo-glyceraldehyde-3-phosphate dehydrogenase (apo-GAPDH) from Synechococcus PCC 7942 is reported. The crystal structure was solved by molecular replacement and refined to an R of 21.7% and R(free) of 27.5% at 2.9 angstroms resolution. The structural features of apo-GAPDH are as follows. The S-loop has an extremely flexible conformation and the sulfate ion is only taken into the classical P(i) site. A structural comparison with holo-GAPDHs indicated that the S-loop fixation is essential in the discrimination of NADP and NAD molecules.