Flavodoxins are electron transfer proteins which contain one FMN molecule as the redox active component. The article reviews the structures of flavodoxins from bacteria and algae determined at high resolution and their functional implications. Each flavodoxin has a core of five parallel β-strands surrounded by α-helices. Although the FMN binds to similar position in the protein to each other, the environment of the isoalloxazine ring of FMN differs. It appears that there are various modes of structural changes associated with conversion of the redox states. The relationship between the environment of the isoalloxazine ring and the potential for the oxidized/semiquinone couple is discussed.
