Presenting Author Howard Hughes Medical Institute; Cornell University
All radical-SAM enzymes require [4Fe-4S] clusters for activity. It is well known the [4Fe-4S] cluster is very air sensitive and requires strict anaerobic conditions to reconstitute activity in vitro. However, aerobic species that live under oxygen do use radical SAM enzymes. How such enzymes function in vivo in the presence of oxygen is an interesting question. My lab works on the yeast diphthamide biosynthetic noncanonical radical-SAM enzyme Dph1-Dph2. Consistent with the known oxygen sensitivity, we found that in vitro the [4Fe-4S] cluster in Dph1-Dph2 is easily degraded into a [3Fe-4S] cluster. Remarkably, a small iron-containing protein Dph3 can donate one Fe atom to convert the [3Fe-4S] cluster in Dph1-Dph2 to a functional [4Fe-4S] cluster during the radical-SAM enzyme catalytic cycle. We believe this is a general strategy to solve the oxygen sensitivity problem and Dph3-like proteins may exist to keep other radical-SAM enzymes functional in aerobic environments.
