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Negative stain EM Map of the AAA protein CbbX, a red-type Rubisco activase from R. sphaeroides
Structural highlights
FunctionCBBX_CERSP ATPase involved in the activation of red-type RuBisCo (ribulose-1,5-bisphosphate carboxylase/oxygenase), which tends to form inactive complexes with its substrate ribulose 1,5-bisphosphate (RuBP) (PubMed:27872295, PubMed:22048315). Catalyzes the release of RuBP from inhibited RuBisCo in an ATP-dependent manner (PubMed:27872295, PubMed:22048315). Activation of RuBisCO involves the ATP-dependent carboxylation of the epsilon-amino group of lysine leading to a carbamate structure (PubMed:27872295, PubMed:22048315).[1] [2] Publication Abstract from PubMedRibulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyses the fixation of atmospheric CO(2) in photosynthesis, but tends to form inactive complexes with its substrate ribulose 1,5-bisphosphate (RuBP). In plants, Rubisco is reactivated by the AAA(+) (ATPases associated with various cellular activities) protein Rubisco activase (Rca), but no such protein is known for the Rubisco of red algae. Here we identify the protein CbbX as an activase of red-type Rubisco. The 3.0-A crystal structure of unassembled CbbX from Rhodobacter sphaeroides revealed an AAA(+) protein architecture. Electron microscopy and biochemical analysis showed that ATP and RuBP must bind to convert CbbX into functionally active, hexameric rings. The CbbX ATPase is strongly stimulated by RuBP and Rubisco. Mutational analysis suggests that CbbX functions by transiently pulling the carboxy-terminal peptide of the Rubisco large subunit into the hexamer pore, resulting in the release of the inhibitory RuBP. Understanding Rubisco activation may facilitate efforts to improve CO(2) uptake and biomass production by photosynthetic organisms. Structure and function of the AAA+ protein CbbX, a red-type Rubisco activase.,Mueller-Cajar O, Stotz M, Wendler P, Hartl FU, Bracher A, Hayer-Hartl M Nature. 2011 Nov 2;479(7372):194-9. doi: 10.1038/nature10568. PMID:22048315[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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