Understanding the mechanistic details of how proteins recognize, manipulate and modify other molecules requires detailed knowledge of their structures. In Professor Kimber's lab, x-ray crystallography is used as the primary tool to probe the molecular architecture of biological objects; the resul...
Understanding the mechanistic details of how proteins recognize, manipulate and modify other molecules requires detailed knowledge of their structures. In Professor Kimber's lab, x-ray crystallography is used as the primary tool to probe the molecular architecture of biological objects; the resulting detailed, three-dimensional models provide the context for interpreting established research findings and generating concrete functional hypothesis. These are then tested using further biochemical experiments to tease out the critical structure-function relationships.
At present, Professor Kimber's lab is primarily focused on elucidating the structural organization of the carboxysome. Carboxysomes are large (up to 200 nm), icosahedral bodies found in the cytoplasm of cyanobacteria that catalyse the critical reaction that incorporates atmospheric CO2 into nascent sugars. Carboxysomes are made exclusively of protein, with a thin shell which is built from a handful of small proteins by tiling thousands of copies into continusous triangular sheets.
The interior core is stuffed primarily with the CO2 fixing enzyme, RuBisCO, but also contains several other proteins that mediate a complex network of interactions necessary to structure and organize the body. The carboxysome appears to promote efficient carbon fixation by using its shell to confine CO2 near RuBisCO so that it is fixed, rather than escaping by diffusing through the cellular membranes. Most models of their functioning therefore imply that the shell traps CO2 but allows bicarbonate and other metabolites to pass – i.e. it effectively functions as a selectively permeable, but purely protein, membrane.
Above and beyond this effect, the supermolecular organization of this complex possibly results in the emergence of new functional properties that further promote the efficiency of this critical biochemical process. His laboratory is using crystallography to solve the structures of individual carboxysome components, while in parallel using a variety of techniques to investigate their higher order organization. Ultimately they aim to understand the structural basis of the carboxysome’s unique properties.