Research reveals Mechanism underlying CO2 Biosequestration

Cyanobacteria have evolved an environmental-adaptation CO2 concentrating mechanism (CCM), which improves photosynthetic performance especially under limited CO2 concentration. Cyanobacterial CCM is composed of a unique microcompartment called carboxysome, where Rubisco is present, and five distinct transport systems for Ci (HCO3- and CO2) uptake. Among them, BicA, SbtA and BCT1 are three significant HCO3- transporters. SbtA and BicA are sodium-dependent HCO3- transporters with high and medium affinity, respectively. A research team led by Dr. Peng Zhang from CAS Center for Excellence in Molecular Plant Sciences (CEMPS) aimed to study the mechanism of bicarbonate transporters in CCM, and reported the structure and transport mechanism of BicA in a previous study (Nat Plants, 2019).

In the current study, Dr. Peng Zhang’s group continued the research by determining the three-dimensional structure of the SbtA-SbtB complex in both the presence and absence of HCO3- and/or AMP. Analysis of the inward-facing state of the SbtA structure reveals the HCO3-/Na+ binding site, providing evidence for the functional unit as a trimer. Structural comparison suggests that SbtA adopts an elevator mechanism for bicarbonate transport. Structural-based functional analysis reveals that the allosteric inhibition of SbtA by SbtB occurs mainly through the T-loop of SbtB, and the latter binds both the core domain and the scaffold domain of SbtA and locks it in an inward-facing state. The conformation of T-loop can be adjusted by the AMP and/or cAMP molecules that are indicators of the cell energy state.

The research article entitled “Molecular mechanism underlying transport and allosteric inhibition of bicarbonate transporter SbtA” has been published online in the prestigious international journal PNAS on May 24, 2021.

The transport and regulatory mechanism revealed by this study is important to understand the inorganic carbon uptake systems in CCM, which can be further used to improve photosynthesis efficiency in plants and boost the biosequestration of carbon dioxide.

This work was supported by National Key R&D Program of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences, and the Shanghai Science and Technology Commission.


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Dr. Peng Zhang, Professor
National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Chinese Academic of Sciences
Tel: +86-21-54924219