About Neuroglobin/ NGB:
Neuroglobin is a molecule, typically found in mammals, which is closely related to haemoglobin in red blood cells, and myoglobin found in muscle cells. Neuroglobin is a respiratory protein which helps to deliver oxygen to nerve cells in the brain and the nervous system. It is a cell-specific oxygen delivery mechanism that evolved to cater to the specific needs of nerve cells.
The precise way neuroglobin (NGB) works remains unclear to researchers. Currently, there are several hypotheses for the role of this protein in the body. One idea is that the function of neuroglobin is to supply oxygen to the retina - widely considered a part of the brain which extends outward from the frontal cortex to the back of the eye. Neuroglobin, therefore, could be seen as a specialised oxygen delivery vehicle for this sensitive tissue.
Another theory is that neuroglobin is a free radical scavenger. Its role is to collect reactive oxygen species in its proximity, preventing them from harming cellular capacity for reading the genome and expressing the epigenome.
Neuroglobin expression is confined to cells in the central and peripheral nervous system, as well as specific hormone-producing tissues. Expression of the protein is highest in the retina, with many times the concentrations found compared to elsewhere in the bodies of vertebrates. Neuroglobin is not believed to have the same evolutionary ancestry as the related cytoglobin. Researchers believe that cytoglobin shared a common ancestor with myoglobin, while neuroglobin had its roots in invertebrate nerve globins.
The precise role that neuroglobin play remains unclear, as discussed. But they may have evolved out of a need to find ways to protect the body from hypoxic or ischaemic insult. Animals could quite easily find themselves underwater for long periods or experience blockages in their arteries, preventing oxygenated blood from reaching the brain and other peripheral tissues. Neuroglobins may have helped in these circumstances by transporting oxygen across the blood-brain barrier even when blood levels were running low.
Although preserving oxygen status is the leading accepted role of neuroglobin, it may not be the only. It’s possible that its role extends beyond neuronal oxygen homeostasis and into other areas. Its concentration in the retina remains to be explained.
Neuroglobina and cytoglobin are both relatively recent additions to the family of respiratory proteins currently known to science. These respiratory proteins contain heme, a structure which binds to oxygen and delivers this vital, life-giving chemical to cells.
Neuroglobins appears to be similar in structure to the better-studied myoglobin. However, neuroglobins have better resilience to heat shock, able to withstand extreme increases in temperature that myoglobin cannot. Small voids or pockets within the chemical structure of neuroglobin may convey this resistance, giving it its strength.
Neuroglobin’s hexacoordinate structure is similar to cytochrome c, a chemical which reduces nitrite to NO when it goes through a transition to pentacoordinate. The most common structural feature of all the globins, including neuroglobin, is a histidine side chain binding to the sixth coordination site of the heme component all these proteins carry.