New Chemical Strategy for Conversion of CO2 to Biomass

acetone carboxylase
Upon nucleotide binding, acetone carboxylase undergoes conformational shifts, opening an internal solvent channel. (a) Ligand-free structure showing a substrate channel (grey) linking the nucleotide binding site to the outside solvent and allowing adenosine triphosphate (ATP) cofactor and carbon dioxide (CO2) substrate to enter. Access to the manganese (Mn) active site is closed by an α-helix in the path. (b) The adenosine monophosphate (AMP)–bound structure shows an opening of an internal channel (grey) linking the nucleotide binding site to the Mn active site. The blocking helix becomes a disordered loop when AMP is bound. [From Mus, F., et al. “Structural Basis for the Mechanism of ATP-Dependent Acetone Carboxylation.” Nat. Sci. Rep. 7, Article 7234 (2017). DOI:10.1038/s41598-017-06973-8. Reused under a Creative Commons license (CC by 4.0, https://creativecommons.org/licenses/by/4.0/).]
A research team has uncovered a new mechanism for enzyme-mediated carbon dioxide (CO2) capture and conversion. They have revealed new and unique elements of carboxylation chemistry (CC) that could be used in catalytic strategies for converting CO2 into chemical feedstock or biomass. The crystal structure of acetone carboxylase (AC; enzyme involved in biodegradation by bacteria) was solved using X-ray crystallographic data. The inactive, unbound (apo) structure shows a substrate channel blocked off from the manganese (Mn) active site where CO2 conversion takes place. An adenosine monophosphate (AMP)–bound structure contains large conformational changes that open the channel to the active site. Highly reactive intermediates in the channel are protected from outside solvent as they are transported to the Mn active site for CO2 conversion. Stepwise mechanisms of carboxylation reactions differ in essential ways with respect to co-substrate, co-factor, and metal requirements. Knowledge of these mechanisms provides the basis for an increased fundamental understanding of CC, contributing to future strategies for CO2 capture and conversion to biomass. These in turn may mitigate the effects of increasing concentrations of CO2 on the global climate.

Mus, F., et al. “Structural Basis for the Mechanism of ATP-Dependent Acetone Carboxylation.” Nat. Sci. Rep. 7, Article 7234 (2017). [DOI:10.1038/s41598-017-06973-8].

Instruments and Facilities Used: X-ray crystallographic data from the Stanford Synchrotron Lightsource (SSLS) at SLAC National Accelerator Laboratory (SLAC). Structural data from macromolecular crystallography were measured on SSLS beamline 12-2; Advanced Photon Source (APS) at Argonne National Laboratory (ANL); and the Diamond Light Source, Oxfordshire, United Kingdom.