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Chaperone Machineries in RuBisCO Biogenesis and Metabolic Repair

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Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is not only the most abundant protein in nature but also one with a remarkably high chaperone requirement for its biogenesis and metabolic maintenance.

Although by the mid-1990s it was clear that the chaperonin system is required for the folding of the large subunit of RuBisCO, the enzyme could not be reconstituted in vitro. In 2007, the structure and mechanism of action of the first specific assembly chaperone of RuBisCO, the protein RbcX, was reported. More recently, analysis of the protein Raf1 showed that this protein, like RbcX, is also involved in the assembly of RuBisCO. Interestingly, the mechanisms by which RbcX and Raf1 assist RuBisCO assembly differ substantially.

To become catalytically active, the newly-assembled RuBisCO must first be carbamylated by a non-substrate CO2 molecule at the active-site lysine and bind a Mg2+ ion as cofactor. Premature binding of the substrate ribulose-1,5-biphosphate (RuBP) results in an inactive complex. Inactivation of RuBisCO also occurs during its multistep catalytic reaction, due to the production of ‘misfire’ products such as XuBP or PDBP . Reactivation is catalyzed by a AAA + (ATPases Associated with various cellular Activities) protein called RuBisCO activase (Rca). More recently, the discovery of the phosphatase XuBPase, which hydrolyzes the inhibitory sugar phosphate XuBP, demonstrated the importance of a functional cooperation of Rca with specific phosphatases in maintaining RuBisCO activity during photosynthesis.

This talk is part of the What's on in Plant Sciences series.

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