The students in Catherine Drennan’s chemistry classes are silent with attention when she says the word “energy.” They listen more
intensely when she couples energy with the environment and pollution. For example, she tells them, it might be possible to use obscure chemical processes of microorganisms to simultaneously scrub carbon dioxide from coal smokestacks and produce fuel from the CO2 waste product of energy production.
“When I began working on environmentally relevant enzymes about 12 years ago, it was a bizarre little thing,” says Drennan, a professor of chemistry at MIT who is, uniquely, both a Howard Hughes Medical Institute Investigator and a Howard Hughes Medical Institute Professor recognized for outstanding undergraduate education. She was attracted to this combination of chemistry and biology because of the intriguing chemistry that some microbial enzymes carry out, including those that contribute to the global carbon cycle.
Many organisms produce enzymes with metal atoms stashed away in their centers — metallocenters. But some microorganisms produce unusual enzymes with nickel centers and uncommon enzymes containing vitamin B12 (which has a cobalt metallocenter). Such enzymes can use the nickel or the cobalt of B12 to form bonds with carbon, which effectively sequesters carbon dioxide out of the environment and converts it into fuel for growth.
Drennan has long asked herself if such microbes could help mitigate CO2 emissions from energy production and consumption. Could we grow organisms that do more of their natural catalytic activity? This interest made her a natural fit for the MIT Energy Initiative (MITEI). Partly because of MITEI, Drennan’s work is morphing from extremely basic to more applied research.
Now, she envisions a two-microbe system that removes carbon dioxide from the environment and converts it into energy. One nickel-centered bacterium, Moorella thermoacetica, would “eat” CO2 and make acetate, a common carbon energy source for cells. A second bacterium eats acetate and makes electrons. “We could grow the acetate-eating microbes on electrodes to produce electricity from CO2,” she says.
Drennan, whose work is supported by MITEI’s Energy Research Seed Fund Program via funds from the Singapore-MIT Alliance, is working with other MITEI researchers interested in applying these and similar ideas to energy problems. What do her colleagues need to know about these enzymes to go forward? Do smokestack emissions contain components that inhibit these enzymes? Can we increase the types of molecules these enzymes will accept? “There are so many smart people working on different aspects of these problems that the field is progressing faster than I anticipated.”
Drennan uses structural techniques like x-ray crystallography to also study other environmentally relevant enzymes. For example, the process of making many pharmaceuticals involves halogenation, which adds chloride or bromide to a natural product and produces toxic byproducts. Likewise, an enzyme used in the 13-step organic synthesis of the vitamin biotin produces harmful waste products. “We want to use enzymes to replace the unfriendly organic chemistry and produce less waste.”
In addition to research, Drennan loves training the next generation of scientists who want to use chemistry to solve energy and environmental problems. “They will have new technologies and will be able to answer questions we can’t today” especially, she adds, if MIT alumni lend their expertise in science, engineering, economics, and business to the field.