1ej7
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CRYSTAL STRUCTURE OF UNACTIVATED TOBACCO RUBISCO WITH BOUND PHOSPHATE IONS
OverviewOverview
d-Ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) catalyses the, central CO(2)-fixing reaction of photosynthesis in a complex, multiple-step process. Several structures of rubisco complexed with, substrate analogues, inhibitors and products have been determined by X-ray, crystallography. The structures fall into two well-defined and distinct, states. The active site is either "open" or "closed". The timing and, mechanism of the transition between these two states have been uncertain., We solved the crystal structure of unactivated (metal-free) rubisco from, tobacco with only inorganic phosphate bound and conclude that phosphate, binding per se does not trigger closure, as it does in the similarly, structured enzyme, triosephosphate isomerase. Comparison of all available, rubisco structures suggests that, instead, the distance between the, terminal phosphates (P1 and P2) of the bisphosphate ligand is the trigger:, if that distance is less than 9.1 A, then the active site closes; if it is, greater than 9.4 A then the enzyme remains open. Shortening of the, inter-phosphate distance results from the ligand binding in a more curved, conformation when O atoms of the ligand's sugar backbone interact either, with the metal, if it is present, or with charged groups in the, metal-binding site, if the metal is absent. This shortening brings the P1, phosphate into hydrogen bonding contact with Thr65. Thr65 exists in two, discrete states related by a rotation of the backbone psi torsion angle., This rotation is coupled to domain rotation and hence to active site, closure. Rotation of the side-chain of Thr65 also affects the C-terminal, strand of large subunit which packs against Loop 6 after closure. The, position of the C-terminal strand in the closed state is stabilised by, multiple polar interactions with a distinctive highly-charged latch site, involving the side-chain of Asp473. In the open state, this latch site may, be occupied instead by phosphorylated anions.
About this StructureAbout this Structure
1EJ7 is a Protein complex structure of sequences from Nicotiana tabacum with PO4 as ligand. Active as Ribulose-bisphosphate carboxylase, with EC number 4.1.1.39 Full crystallographic information is available from OCA.
ReferenceReference
The transition between the open and closed states of rubisco is triggered by the inter-phosphate distance of the bound bisphosphate., Duff AP, Andrews TJ, Curmi PM, J Mol Biol. 2000 May 19;298(5):903-16. PMID:10801357
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