DOE User Facilities Help Explain Workings of Key Metabolic Enzyme

Summary

Carbonic anhydrase (CA) converts bicarbonate ion to carbon dioxide and back. It is a key part of the metabolism of humans, animals, plants, and microbes that involves carbon dioxide. Engineered and stabilized forms of CA are being studied for use to capture CO₂ from flue gas at coal-fired power plants and as part of algal biofuel production. Three recent publications improve our understanding of how CA works using the unique capabilities of DOE’s National Synchrotron Light Source (NSLS) and Los Alamos Neutron Science Center (LANSCE). X-ray crystallography at the NSLS was used to show how human CA recognizes molecules to which it might bind. These data support the authors’ hypothesis from thermodynamic considerations that “the shape of the water in the (HA) binding cavity may be as important as the shape of the cavity.” The second study, used neutron diffraction of human CA at LANSCE to show that the catalytic site CA changes when the pH of the water around it decreases from 10.0 to 7.8. This observation, the first of its kind, enabled the authors to define more clearly the proton transfer that occurs when CA catalyzes the carbon dioxide—bicarbonate conversion. These studies will help scientists re-engineering CA designs for CO₂ capture, biofuel production, and other applications.

The NSLS studies were carried out by scientists at Brookhaven’s Macromolecular Crystallography Research Resource jointly with scientists from Harvard University, while the LANSCE experiments were carried out by scientists at Los Alamos’ Protein Crystallography Station in collaboration with scientists from the University of Florida.

References

Snyder, P.W., et al. 2011. “Mechanism of the Hydrophobic Effect in the Biomolecular Recognition of Arylsulfonamides by Carbonic Anhydrase,” Proceedings of the National Academy of Sciences (USA), DOI: 10.1073/pnas.1114107108.

[Discussed in Ball, P. 2011. “Biophysics: More Than a Bystander,” Nature 478, 467-68. (DOI:10.1038/478467a)]

Mecinovic, J., et al. 2011. “Fluoroalkyl and Alkyl Chains Have Similar Hydrophobicities in Binding to the ‘Hydrophobic Wall’ of Carbonic Anhydrase,” Journal of the American Chemical Society 133, 14017. DOI: 10.1021/ja2045293.

Fisher, Z., et al. 2011 “Neutron Structure of Human Carbonic Anhydrase II: A Hydrogen-Bonded Water Network “Switch” Is Observed Between pH 7.8 and 10.0,” Biochemistry 50, 9421-23. DOI: 10.1021/bi201487b.