In search of new insights into nitrogenase

Kathryn Fixen received a five-year NSF CAREER Award to investigate how to get an enzyme that catalyzes nitrogen fixation to work on plants.
January 18, 2024
Kathryn Fixen

Kathryn Fixen, an assistant professor in the Department of Plant and Microbial Biology, recently received a $1M National Science Foundation (NSF) CAREER Award to support her lab’s efforts to find promising pathways toward the long-sought-after goal to introduce nitrogenase — the enzyme responsible for nitrogen fixation — directly into plants. She shared a bit of background about her research and the reason she’s pursuing this line of inquiry.

How does this award fit into the work happening in your lab?
One of the things that my lab is really focused on is nitrogen fixation, which is how bacteria take nitrogen gas out of the atmosphere and essentially turn it into fertilizer. The NSF award will support my lab’s efforts to better understand how we can connect nitrogenase, an enzyme involved in nitrogen fixation, to a plant's metabolism. 

What appeals to you about this particular research question?
People have wanted to engineer nitrogen fixation  into plants for decades as a way to reduce the need to use an industrial process known as the Haber-Bosch process to make or fertilizer. The process requires lots of energy in the form of fossil fuels. So even though it's been incredibly useful in improving crop production and expanding our population worldwide, the goal is to find ways to get away from using the process. Once people figured out which enzyme is involved in nitrogen fixation in the 1960s, the assumption was that we would quickly find a way to put it into plants and get them to start fixing their own nitrogen. That has yet to happen because, as it turns out, it’s incredibly challenging. 

What are the particular challenges involved?
Nitrogenase is really sensitive to oxygen. It's a really complex enzyme. Recently, there’s been progress toward showing that you can actually get plants to make at least components of this enzyme that are functional. This particular enzyme requires a lot of energy, and it needs a lot of electrons to carry out its chemistry. Bacteria have proteins that form a sort of wire to this enzyme to deliver these electrons. Plants do have some of the same proteins, so then the next question is, once we get it into plants, can it work?

How will you go about identifying promising directions for this work?
We are going to use bacteria as a chassis to evolve these plant proteins to work better with nitrogenase. Because it's so difficult to make nitrogenase in a plant, we're trying it out in bacteria using new genome engineering tools as well as directed evolution first.

— Stephanie Xenos