De novo design of symmetric ferredoxins that shuttle electrons in vivo

Significance Early life is thought to have evolved from simple building blocks that were propagated through gene duplication events. A classic example is the small soluble iron-sulfur containing protein, bacterial ferredoxin, which is an asymmetric dimer, an essential component of many extant electron transfer chains and has ancient origins. To probe the theoretical gene duplication origins of bacterial ferredoxins, we designed a series of synthetic symmetric constructs. All designs bound two iron-sulfur clusters and were able to support electron transfer between a pair of oxidoreductases in vivo inEscherichia coli . Our results strongly suggest that simple, symmetric ancestral proteins probably evolved early in Earth’s history and can be engineered to facilitate functional electron transfer in synthetic metabolic pathways.