Scientists from the University of Liverpool and Newcastle University have taken an important step toward understanding how bacterial organelles come together. In their case, they are interested in getting design inspiration from a structure called the carboxysome. This fundamental biological study uncovers the inner workings of these organelles to further elucidate their involvement in carbon capture pathways. It could open the door to ambitious new bioengineering and climate-positive solutions.
The carboxysome has an important function in carbon fixation, as it contains high concentrations of the enzyme carbonic anhydrase. This enzyme is especially remarkable, having produced a unique hexameric structure, six joined individual pieces. Until now, scientists thought that encapsulation of carbonic anhydrase within the carboxysome would need a special linker protein to mediate that process. This latest study demonstrates that we can trap the enzyme inside the structure through dynamic, non-covalent interactions with divergent shell proteins. This unexpected finding upended previous beliefs about enzyme encapsulation.
To carry out this research, the team used the latest structural biology tools, such as single-particle cryo-electron microscopy. This recently developed technique gave the scientists the ability to capture ultra-high-resolution, almost atomic-level detail of the carbonic anhydrase enzyme, dubbed CsoSCA. The model bacterium used for these studies was Halothiobacillus neapolitanus, which has one of the most efficient carbon-fixing pathways described to date.
An important finding of the study is the interaction between carbonic anhydrase and another critical enzyme, Rubisco, which is essential for carbon dioxide fixation. This interaction further points to a modular “toolkit” design that bacteria use to maximise their carbon-capture machinery. Such mechanistic understandings of the functional dynamics of these catalytic power houses would prove tremendously impactful toward fostering the next generation of sustainable biotechnologies.
To better understand how carbonic anhydrase is recruited and organized within the protein cages, the scientists designed synthetic “mini-shells.” This was a novel art implementation that gave new structural evidence of the enzyme’s encapsulation and organization within the carboxysome.
Professor Luning Liu, Chair of Microbial Bioenergetics and Bioengineering at the University of Liverpool, the study’s leader. He was accompanied by Dr. Jon Marles-Wright, the co-author—and Academic Lead for Electron Microscopy—at Newcastle University. Their collaborative effort led to important findings that were recently published in the Proceedings of the National Academy of Sciences.