Crystal structure of activated tobacco rubisco complexed with the reaction-intermediate analogue 2-carboxy-arabinitol 1,5-bisphosphate.

The crystal structure of activated tobacco rubisco, complexed with the reaction-intermediate analogue 2-carboxy-arabinitol 1,5-bisphosphate (CABP) has been determined by molecular replacement, using the structure of activated spinach rubisco (Knight, S., Andersson, I., & Brändén, C.-I., 1990, J. Mol. Biol. 215, 113-160) as a model. The R-factor after refinement is 21.0% for 57,855 reflections between 9.0 and 2.7 A resolution. The local fourfold axis of the rubisco hexadecamer coincides with a crystallographic twofold axis. The result is that the asymmetric unit of the crystals contains half of the L8S8 complex (molecular mass 280 kDa in the asymmetric unit). The activated form of tobacco rubisco is very similar to the activated form of spinach rubisco. The root mean square difference is 0.4 A for 587 equivalent C alpha atoms. Analysis of mutations between tobacco and spinach rubisco revealed that the vast majority of mutations concerned exposed residues. Only 7 buried residues were found to be mutated versus 54 residues at or near the surface of the protein. The crystal structure suggests that the Cys 247-Cys 247 and Cys 449-Cys 459 pairs are linked via disulfide bridges. This pattern of disulfide links differ from the pattern of disulfide links observed in crystals of unactivated tobacco rubisco (Curmi, P.M.G., et al., 1992, J. Biol. Chem. 267, 16980-16989) and is similar to the pattern observed for activated spinach tobacco.