3SYL: Crystal structure of the AAA+ protein CbbX, native structure

Ribulose 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.
PDB ID: 3SYLDownload
MMDB ID: 94919
PDB Deposition Date: 2011/7/18
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 3  Å
Source Organism:
Similar Structures:
Biological Unit for 3SYL: dimeric; determined by software (PISA)
Molecular Components in 3SYL
Label Count Molecule
Proteins (2 molecules)
Protein Cbbx
Molecule annotation
Chemicals (6 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB