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Cytoglobin

Mammalian protein found in Homo sapiens

Summary

Mammalian protein found in Homo sapiens

Cytoglobin is the protein product of CYGB, a human and mammalian gene.

Cytoglobin is a globin molecule ubiquitously expressed in all tissues and most notably utilized in marine mammals. It was discovered in 2001 in hepatic stellate cells during liver fibrosis. Thus, it was originally called "stellate cell activated protein" or STAP. It received its current name in 2002. It is thought to help in the distribution and storage of oxygen as well as protect against hypoxia by scavenging reactive oxygen species . The predicted function of cytoglobin is the facilitation of oxygen among tissues that don't express myoglobin.

Function

Cytoglobin is a ubiquitously expressed hexacoordinate hemoglobin that may facilitate diffusion of oxygen through tissues, scavenge nitric oxide or reactive oxygen species, or serve a protective function during oxidative stress.

Structure

Cytoglobin has 30-40% sequence homology with myoglobin, and has a similar oxygen binding affinity. One of the major differences is the presence of a 20 amino acids extension at both the n and c terminus.

Cytoglobin is a hexacoordinate heme protein. The heme iron in coordinated with histidine residues on both sides, HisF8 and HisE7. The HisE7 is considered to be an "endogenous ligand." In order for oxygen or another gaseous ligand to bind, the HisE7 must dissociate from the iron, making the binding kinetics relatively slow.

Diagram of how the heme group in cytoglobin interacts with the surrounding amino acids of the globin protein. Normally, the iron is coordinated with histidine residues on both sides. The HisE7 must be dissociated in order for oxygen to bind.

In an oxidizing environment, a disulfide bond between Cys38 and Cys83 of the protein forms and causes a conformational change to move HisE7 out of the way, allowing oxygen to bind. Thus, oxygen binding is dependent on the redox state of the tissue.

Applications

CYGB expression can be used as a specific marker with which hepatic stellate cells can be distinguished from portal myofibroblasts in the damaged human liver.

References

(Jul 2001). "Characterization of a stellate cell activation-associated protein (STAP) with peroxidase activity found in rat hepatic stellate cells". The Journal of Biological Chemistry.
(December 2002). "Neuroglobin and cytoglobin: Fresh blood for the vertebrate globin family". EMBO Reports.
(Apr 2002). "Cytoglobin: a novel globin type ubiquitously expressed in vertebrate tissues". Molecular Biology and Evolution.
(20 December 2007). "Why Diving Marine Mammals Resist Brain Damage from Low Oxygen". ScienceDaily.
"Entrez Gene: CYGB cytoglobin".
(May 2002). "A ubiquitously expressed human hexacoordinate hemoglobin". The Journal of Biological Chemistry.
(2022-04-01). "The role of globins in cardiovascular physiology". Physiological Reviews.
(2005-01-01). "Neuroglobin and cytoglobin in search of their role in the vertebrate globin family". Journal of Inorganic Biochemistry.
(Feb 2014). "Cytoglobin is expressed in hepatic stellate cells, but not in myofibroblasts, in normal and fibrotic human liver". Laboratory Investigation.

Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

hemoproteins

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