Flavodoxin, conserved site, protein family

Flavodoxins (Fld) are small, soluble electron-transfer proteins. Flavodoxins contain flavin mononucleotide as prosthetic group. The structure of flavodoxin is characterized by a five-stranded parallel beta sheet, surrounded by five alpha helices. They have been isolated from prokaryotes, cyanobacteria, and some eukaryotic algae.

== Background == Originally found in cyanobacteria and clostridia, flavodoxins were discovered over 50 years ago. These proteins evolved from an anaerobic environment, due to selective pressures. Ferredoxin, another redox protein, was the only protein able to be used in this manner. However, when oxygen became present in the environment, iron became limited. Ferredoxin is iron-dependant as well as oxidant-sensitive. Under these limited iron conditions, ferredoxin was no longer preferred. Flavodoxin on the other hand is the opposite of these traits, as it is oxidant-resistant and has iron-free isofunctional counterparts. Therefore, for some time flavodoxin was the primary redox protein. Now however, when ferredoxin and flavodoxin are present in the same genome, ferredoxin is still used but under low iron conditions, flavodoxin is induced.