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Degradation of potent Rubisco inhibitor by selective sugar phosphatase

Nature Plants volume 1, Article number: 14002 (2015) | Download Citation


  • An Erratum to this article was published on 14 January 2015


Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyses the conversion of atmospheric carbon dioxide into organic compounds in photosynthetic organisms. Alongside carboxylating the five-carbon sugar ribulose-1,5-bisphosphate (RuBP)1,​2,​3, Rubisco produces a small amount of xylulose-1,5-bisphosphate (XuBP), a potent inhibitor of Rubisco4. The AAA+ protein Rubisco activase removes XuBP from the active site of Rubisco in an ATP-dependent process5,6. However, free XuBP rapidly rebinds to Rubisco, perpetuating its inhibitory effect. Here, we combine biochemical and structural analyses to show that the CbbY protein of the photosynthetic bacterium Rhodobacter sphaeroides and Arabidopsis thaliana is a highly selective XuBP phosphatase. We also show that CbbY converts XuBP to the non-inhibitory compound xylulose-5-phosphate, which is recycled back to RuBP. We solve the crystal structures of CbbY from R. sphaeroides and A. thaliana, and through mutational analysis show that the cap domain of the protein confers the selectivity for XuBP over RuBP. Finally, in vitro experiments with CbbY from R. sphaeroides reveal that CbbY cooperates with Rubisco activase to prevent a detrimental build-up of XuBP at the Rubisco active site. We suggest that CbbY, which is conserved in algae and plants, is an important component of the cellular machinery that has evolved to deal with the shortcomings of the ancient enzyme Rubisco.

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We thank J. Soll (LMU Munich, Germany) for A. thaliana cDNA, J. Andralojc and M. Parry (Rothamsted, England) for the initial XuBP, and the JSBG group at ESRF Grenoble, as well as staff at SLS-X06DA and X10SA Villigen, MPIB Crystallization Facility and MPIB Core Facility for their excellent support.

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Author notes

    • Andreas Bracher
    •  & Anurag Sharma

    These authors contributed equally to this work

    • Amanda Starling-Windhof

    Present address: Chemical Abstracts Service, 2540 Olentangy River Road, Columbus, Ohio 43202, USA


  1. Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany

    • Andreas Bracher
    • , Anurag Sharma
    • , Amanda Starling-Windhof
    • , F. Ulrich Hartl
    •  & Manajit Hayer-Hartl


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A.B. solved the crystal structures and planned and supervised the experiments. A.S. designed and performed the experiments. The initial crystal screening and preliminary phosphatase analysis was performed by A-S.W. The project was initiated by M.H-H. and F.U.H. and M.H-H. planned and supervised the project. All authors analysed the data and the manuscript was written by A.B., F.U.H. and M.H-H.

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The authors declare no competing financial interests.

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Correspondence to Andreas Bracher or Manajit Hayer-Hartl.

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