Globin

Not to be confused with globulin or globular protein.

Globin family
the Structure of deoxyhemoglobin Rothschild 37 beta Trp----Arg: a mutation that creates an intersubunit chloride-binding site.
Identifiers
Symbol	Globin
Pfam	PF00042
Pfam clan	CL0090
InterPro	IPR000971
PROSITE	PS01033
SCOP	1hba
SUPERFAMILY	1hba
CDD	cd01067
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Bac_globin
crystal structure of "truncated" hemoglobin n (hbn) from mycobacterium tuberculosis, soaked with xe atoms
Identifiers
Symbol	Bac_globin
Pfam	PF01152
Pfam clan	CL0090
InterPro	IPR001486
PROSITE	PDOC00933
SCOP	1dlw
SUPERFAMILY	1dlw
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

The globins are a family of globular proteins, which are thought to share a common ancestor. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members of this family include myoglobin and hemoglobin, which both bind the heme (also haem) prosthetic group. Both of these proteins are reversible oxygen binders.

Globins are haem-containing proteins involved in binding and/or transporting oxygen. They belong to a very large and well studied family that is widely distributed in many organisms.

Types

Globins evolved from a common ancestor and can be divided into three groups: single-domain globins, and two types of chimeric globins, flavohaemoglobins and globin-coupled sensors. Bacteria have all three types of globins, while archaea lack flavohaemoglobins, and eukaryotes lack globin-coupled sensors. Several functionally different haemoglobins can coexist in the same species.

Eight globins are known to occur in vertebrates: androglobin, cytoglobin, globin E, globin X, globin Y, haemoglobin, myoglobin and neuroglobin.

Subfamilies

• Leghaemoglobin IPR001032
• Myoglobin IPR002335
• Erythrocruorin IPR002336
• Haemoglobin, beta IPR002337
• Haemoglobin, alpha IPR002338
• Myoglobin, trematode type IPR011406
• Globin, nematode IPR012085
• Globin, lamprey/hagfish type IPR013314
• Globin, annelid-type IPR013316
• Haemoglobin, extracellular IPR014610

Examples

Human genes encoding globin proteins include:

• CYGB
• HBA1, HBA2, HBB, HBD, HBE1, HBG1, HBG2, HBM, HBQ1, HBZ, MB

The globins include:

• Haemoglobin (Hb)

• Myoglobin (Mb)

• Neuroglobin: a myoglobin-like haemprotein expressed in vertebrate brain and retina, where it is involved in neuroprotection from damage due to hypoxia or ischemia. Neuroglobin belongs to a branch of the globin family that diverged early in evolution.

• Cytoglobin: an oxygen sensor expressed in multiple tissues. Related to neuroglobin.

• Erythrocruorin: highly cooperative extracellular respiratory proteins found in annelids and arthropods that are assembled from as many as 180 subunit into hexagonal bilayers.

• Leghaemoglobin (legHb or symbiotic Hb): occurs in the root nodules of leguminous plants, where it facilitates the diffusion of oxygen to symbiotic bacteriods in order to promote nitrogen fixation.

• Non-symbiotic haemoglobin (NsHb): occurs in non-leguminous plants, and can be over-expressed in stressed plants .

• Flavohaemoglobins (FHb): chimeric, with an N-terminal globin domain and a C-terminal ferredoxin reductase-like NAD/FAD-binding domain. FHb provides protection against nitric oxide via its C-terminal domain, which transfers electrons to haem in the globin.

• Globin E: a globin responsible for storing and delivering oxygen to the retina in birds

• Globin-coupled sensors: chimeric, with an N-terminal myoglobin-like domain and a C-terminal domain that resembles the cytoplasmic signalling domain of bacterial chemoreceptors. They bind oxygen, and act to initiate an aerotactic response or regulate gene expression.

• Protoglobin: a single domain globin found in archaea that is related to the N-terminal domain of globin-coupled sensors.

• Truncated 2/2 globin: lack the first helix, giving them a 2-over-2 instead of the canonical 3-over-3 alpha-helical sandwich fold. Can be divided into three main groups (I, II and II) based on structural features.

• HbN (or GlbN): a truncated haemoglobin-like protein that binds oxygen cooperatively with a very high affinity and a slow dissociation rate, which may exclude it from oxygen transport. It appears to be involved in bacterial nitric oxide detoxification and in nitrosative stress.

• Cyanoglobin (or GlbN): a truncated haemoprotein found in cyanobacteria that has high oxygen affinity, and which appears to serve as part of a terminal oxidase, rather than as a respiratory pigment.

• HbO (or GlbO): a truncated haemoglobin-like protein with a lower oxygen affinity than HbN. HbO associates with the bacterial cell membrane, where it significantly increases oxygen uptake over membranes lacking this protein. HbO appears to interact with a terminal oxidase, and could participate in an oxygen/electron-transfer process that facilitates oxygen transfer during aerobic metabolism.

• Glb3: a nuclear-encoded truncated haemoglobin from plants that appears more closely related to HbO than HbN. Glb3 from Arabidopsis thaliana (Mouse-ear cress) exhibits an unusual concentration-independent binding of oxygen and carbon dioxide.

See also

• C-rich stability element
• Globin fold
• globular protein
• hemoglobin
• Heme
• Myoglobin
• Binding Of Heme

References

This article incorporates text from the public domain Pfam and InterPro IPR001486