Flavodoxin: A platform for characterizing the electronic structure and magnetic properties of the neutral semiquinone state in flavoproteins (Review Article)

Flavodoxins are a type of flavoproteins that function as charge (electron) carriers in several metabolic processes of bacteria, cyanobacteria, and green algae. While their physiological functions may seem modest within the flavoprotein family, which includes enzymes in various metabolic pathways, DNA repair, and magnetoreception, they have played a crucial role in elucidating the electronic structure and magnetic properties of the neutral semiquinone state in flavoproteins. This is due to the ease of preparing the semiquinone (paramagnetic) state in high yield, as well as to the possibility of preparing and characterizing flavodoxin mutants or flavodoxins that include a modified flavin active center, as isotopically labelled isoalloxazine rings or different flavin analogs. This minireview describes insights into the electronic structure and magnetic properties of Anabaena flavodoxin, mainly obtained through electron paramagnetic resonance techniques. These results are compared with those obtained from other flavoproteins, and their relevance is analyzed to better understand flavoproteins in general, both to elucidate their different mechanisms and to inform the design of novel bioinspired materials.