CAREER: Assembly and supramolecular organization of bacterial microcompartments

Many bacteria harbor “microcompartments” to help them use unusual food sources, yet very little is known about how these microcompartments are built from their protein components, or how they work. Because both beneficial and harmful bacteria use microcompartments, understanding their assembly and mechanisms of action could allow us to engineer bacterial strains to combat chemical pollution and carbon dioxide surpluses, or conversely to design antibiotics less likely to promote widespread resistance.

The project combines cryo-electron tomography, mathematical modeling and simulation, and biochemical assays to develop a model of how these large protein assemblies are built, mature, and function. This research is part of an increasing trend toward interdisciplinary science, yet many students struggle to cross traditional scientific divisions. Therefore, the project also includes an education plan focused on developing the necessary skills to analyze and interpret the various types of research data in the molecular life sciences.

Group-based projects with raw data will be developed for a large enrollment Bioanalytical Chemistry class. “Best practices” methods will be published for use by other educators.

The best-studied and simplest microcompartment known is the alpha-carboxysome, which allows ocean bacteria to utilize CO2 to build sugars for metabolism. The carboxysome has a protein shell and contains just two enzymes: carbonic anhydrase that converts ocean bicarbonate to CO2, and Rubisco that removes the carbon from CO2 for downstream metabolism.

Carboxysomes are so stable that they are passed from cell to cell, living far longer than the cell that originally made them. In addition, they are so efficient that cells without them die even if they still have the enzymes in the cytoplasm. How the microcompartment is assembled and the enzyme components organize to become a stable, efficient carbon-fixing machine will be studied.

The lessons learned from this detailed study will then be applied to the characterization of a more complex system, the propanediol-utilization compartment that allows Salmonella to thrive in the mammalian gastrointestinal tract. Taken together, these studies of beneficial and pathogenic microcompartments will both provide new insights into prokaryotic metabolism and create blueprints of powerful machines whose redesign could lead to new technologies or whose disruption could treat mammalian illness.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.