Preliminary structural characterization of a methyltransferase involved in rhodoquinone biosynthesis

The primary process of energy production for most eukaryotes involves oxidative respiration via the electron transport chain (ETC). In the ETC, electrons are moved by the electron carrier ubiquinone through membrane‐bound protein complexes that pump protons across the mitochondrial membrane, which creates a proton chemical gradient. This gradient is used to produce adenosine triphosphate, which is the primary source of energy in the cell. Oxygen is the final electron acceptor of the ETC for aerobic organisms, but for organisms that live in low‐oxygen environments, other strategies are required for the ETC to function. One strategy used by many species of bacteria and protists is to produce rhodoquinone, which is a derivative of ubiquinone. Rhodoquinone allows the ETC to function in the absence of oxygen by allowing it to use fumarate as the final electron acceptor. RQ is synthesized by the enzyme RquA, which likely uses ubiquinone as a substrate. Our goal is to structurally characterize RquA to better understand its mechanism of catalysis. We used E. coli to overexpress RquA derived from Pygsuia biforma and Rhodospirillum rubrum with a variety of fusion tags and found that RquA expresses to a high level but is located in inclusion bodies. We have developed refolding procedures to isolate RquA and are now characterizing its structure as well as the substrates required for RQ production. Support or Funding Information This research is funded by the New Frontiers in Research Fund ‐ Exploration Stream