ferredoxin NADP+ reductase is an enzyme that catalyzes the reduction of NADP+ to NADPH. This enzyme belongs to a family of enzymes called oxidoreductases (link to Wiki) that contain iron-sulfur proteins as electron donors and NAD+ or NADP+ as electron acceptors. FAD, flavin adenine dinucleotide (link to Wiki), is also a cofactor of FNR. The ferredoxin NADP+ reductase participates in a general reaction that proceeds as follows:
2 reduced ferredoxin + NADP+ + H+ 2 oxidized ferredoxin + NADPH
Function
In many facultatively anaerobic bacteria, this protein acts as an oxygen sensor modifying gene expression that adapts the cell to anaerobic growth. The activity of FNR regulates the cells ability to metabolize aerobically or anaerobically so that when oxygen is abundant, FNR is destabilized and converted into an inactive form. The protein is activated when there are low oxygen tensions. This function is known as transcriptional sensor-regulation (link?). The predominant pathway in which this regulation occurs is through binding or oxidation-reduction of oxygen in the iron sulfur center, in which the iron serves as the initiating cofactor that interacts with the oxygen when it is abundant. This is a reversibly constitutive regulation pathway.
In its active form, the protein is dimeric and contains a 4Fe-4S2+ cluster and when inactive, the protein is monomeric and containts a 3Fe-4S2+ cluster.
Although facultative anaerobes prefer to use molecular oxygen as the terminal electron acceptor due the high reduction potential, low oxygen stress is able to induce the bacteria to use FNR instead. The transformation involves other proteins such as the sensor regulator system ArcAB, however these regulators are affected by other intermediates. FNR combines the functions of both a sensor and a regulator.
Disease
Relevance
Structural highlights
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