Fumarate reductase: Structural and mechanistic insights from the catalytic reduction of 2-methylfumarate

The soluble fumarate reductase (FR) from Shewanella frigidimarina can catalyse the reduction of 2-methylfumarate with a kcat of 9.0 s−1 and a KM of 32 μM. This produces the chiral molecule 2-methylsuccinate. Here, we present the structure of FR to a resolution of 1.5 Å with 2-methylfumarate bound at the active site. The mode of binding of 2-methylfumarate allows us to predict the stereochemistry of the product as (S)-2-methylsuccinate. To test this prediction we have analysed the product stereochemistry by circular dichroism spectroscopy and confirmed the production of (S)-2-methylsuccinate.