MurA (UDP-N-acetylglucosamine enolpyruvyl transferase) and AroA (EPSP synthase; 5-enolpyruvyl shikimate-3-phosphate synthase) are microbial proteins that are both important antibiotic targets. MurA catalyses the first step in the peptidoglycan pathway, and is inhibited by antibiotic fosfomycin; AroA catalyses the sixth step in the shikimate pathway and is inhibited by glyphosate, the key component of the herbicide Roundup. The enzymes share a similar reaction mechanism, protein fold and exhibit high sequence identity; this leads us to infer that both proteins share a common ancestor. Despite the similarities between the proteins, their inhibitors show narrow specificity (i.e. fosfomycin does not inhibit AroA and glyphosate has no effect upon MurA).

Using Ancestral Sequence Reconstruction (ASR), I plan to retrace the histories of both proteins to a hypothetical common ancestor, able to catalyse both reactions. I have reconstructed the ancestral MurA and AroA proteins from the common ancestor of known Streptococci species (approximately 300 million years ago¹). Both ancestors can rescue their respective E. coli knockout strains and enzyme kinetics have been carried out on the ancestral MurA and that from S. pyogenes.

As I search further back through the pasts of these two enzymes, I hope to recreate a common AroA/MurA ancestral protein and use it to screen for potential broad-spectrum antibiotics.