Cyanidioschyzon merolae ferredoxin: A high resolution crystal structure analysis and its thermal stability

Cyanidioschyzon merolae (Cm) is a single-cell red alga that grows under moderately thermophilic (40–50 °C), acidic (pH 1–3) conditions. We purified a Cm ferredoxin (Fd) that was characterized as a plant-type [2Fe–2S] Fd by physicochemical techniques. X-ray crystallography revealed that the overall three-dimensional structure of CmFd was highly similar to, but slightly different from, the [2Fe–2S] Fd from Spinacia oleracea, whose growth temperature is 15–20 °C. Therefore, slight structural differences, including non-covalent-bond number and amino acid sequence, may underlie the differential thermostabilities of the plant-type Fds.