Recent structural studies have revealed two fundamentally different architectures for natural chorismate mutase enzymes. The monofunctional chorismate mutase from Bacillus subtilis (BsCM) is a symmetric homotrimer, packed as a pseudo-α/β-barrel, with three identical active sites formed at the interface of adjacent subunits. In contrast, the broadly distributed AroQ mutases, which include the allosterically regulated Saccharomyces cerevisiae enzyme and the chorismate mutase domain of the bifunctional Escherichia coli chorismate mutase-prephenate dehydratase, are all-helix proteins with active sites embedded within four-helix bundle units.