Structural highlights
Disease
HBA_HUMAN Defects in HBA1 may be a cause of Heinz body anemias (HEIBAN) [MIM:140700. This is a form of non-spherocytic hemolytic anemia of Dacie type 1. After splenectomy, which has little benefit, basophilic inclusions called Heinz bodies are demonstrable in the erythrocytes. Before splenectomy, diffuse or punctate basophilia may be evident. Most of these cases are probably instances of hemoglobinopathy. The hemoglobin demonstrates heat lability. Heinz bodies are observed also with the Ivemark syndrome (asplenia with cardiovascular anomalies) and with glutathione peroxidase deficiency.[1] Defects in HBA1 are the cause of alpha-thalassemia (A-THAL) [MIM:604131. The thalassemias are the most common monogenic diseases and occur mostly in Mediterranean and Southeast Asian populations. The hallmark of alpha-thalassemia is an imbalance in globin-chain production in the adult HbA molecule. The level of alpha chain production can range from none to very nearly normal levels. Deletion of both copies of each of the two alpha-globin genes causes alpha(0)-thalassemia, also known as homozygous alpha thalassemia. Due to the complete absence of alpha chains, the predominant fetal hemoglobin is a tetramer of gamma-chains (Bart hemoglobin) that has essentially no oxygen carrying capacity. This causes oxygen starvation in the fetal tissues leading to prenatal lethality or early neonatal death. The loss of three alpha genes results in high levels of a tetramer of four beta chains (hemoglobin H), causing a severe and life-threatening anemia known as hemoglobin H disease. Untreated, most patients die in childhood or early adolescence. The loss of two alpha genes results in mild alpha-thalassemia, also known as heterozygous alpha-thalassemia. Affected individuals have small red cells and a mild anemia (microcytosis). If three of the four alpha-globin genes are functional, individuals are completely asymptomatic. Some rare forms of alpha-thalassemia are due to point mutations (non-deletional alpha-thalassemia). The thalassemic phenotype is due to unstable globin alpha chains that are rapidly catabolized prior to formation of the alpha-beta heterotetramers. Note=Alpha(0)-thalassemia is associated with non-immune hydrops fetalis, a generalized edema of the fetus with fluid accumulation in the body cavities due to non-immune causes. Non-immune hydrops fetalis is not a diagnosis in itself but a symptom, a feature of many genetic disorders, and the end-stage of a wide variety of disorders. Defects in HBA1 are the cause of hemoglobin H disease (HBH) [MIM:613978. HBH is a form of alpha-thalassemia due to the loss of three alpha genes. This results in high levels of a tetramer of four beta chains (hemoglobin H), causing a severe and life-threatening anemia. Untreated, most patients die in childhood or early adolescence.[2]
Function
HBA_HUMAN Involved in oxygen transport from the lung to the various peripheral tissues.
Publication Abstract from PubMed
Staphylococcus aureus causes life-threatening disease in humans. The S. aureus surface protein iron-regulated surface determinant H (IsdH) binds to mammalian hemoglobin (Hb) and extracts heme as a source of iron, which is an essential nutrient for the bacteria. However, the process of heme transfer from Hb is poorly understood. We have determined the structure of IsdH bound to human Hb by x-ray crystallography at 4.2 A resolution, revealing the structural basis for heme transfer. One IsdH molecule is bound to each alpha and beta Hb subunit, suggesting that the receptor acquires iron from both chains by a similar mechanism. Remarkably, two near iron transporter (NEAT) domains in IsdH perform very different functions. An N-terminal NEAT domain binds alpha/beta globin through a site distant from the globin heme pocket and, via an intervening structural domain, positions the C-terminal heme-binding NEAT domain perfectly for heme transfer. These data, together with a 2.3 A resolution crystal structure of the isolated N-terminal domain bound to Hb and small-angle x-ray scattering of free IsdH, reveal how multiple domains of IsdH cooperate to strip heme from Hb. Many bacterial pathogens obtain iron from human hemoglobin using proteins that contain multiple NEAT domains and other domains whose functions are poorly understood. Our results suggest that, rather than acting as isolated units, NEAT domains may be integrated into higher order architectures that employ multiple interaction interfaces to efficiently extract heme from host proteins.
Structure of the Hemoglobin-IsdH Complex Reveals the Molecular Basis of Iron Capture by Staphylococcus aureus.,Dickson CF, Kumar KK, Jacques DA, Malmirchegini GR, Spirig T, Mackay JP, Clubb RT, Guss JM, Gell DA J Biol Chem. 2014 Mar 7;289(10):6728-38. doi: 10.1074/jbc.M113.545566. Epub 2014 , Jan 14. PMID:24425866[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Ohba Y, Yamamoto K, Hattori Y, Kawata R, Miyaji T. Hyperunstable hemoglobin Toyama [alpha 2 136(H19)Leu----Arg beta 2]: detection and identification by in vitro biosynthesis with radioactive amino acids. Hemoglobin. 1987;11(6):539-56. PMID:2833478
- ↑ Traeger-Synodinos J, Harteveld CL, Kanavakis E, Giordano PC, Kattamis C, Bernini LF. Hb Aghia Sophia [alpha62(E11)Val-->0 (alpha1)], an "in-frame" deletion causing alpha-thalassemia. Hemoglobin. 1999 Nov;23(4):317-24. PMID:10569720
- ↑ Dickson CF, Kumar KK, Jacques DA, Malmirchegini GR, Spirig T, Mackay JP, Clubb RT, Guss JM, Gell DA. Structure of the Hemoglobin-IsdH Complex Reveals the Molecular Basis of Iron Capture by Staphylococcus aureus. J Biol Chem. 2014 Mar 7;289(10):6728-38. doi: 10.1074/jbc.M113.545566. Epub 2014 , Jan 14. PMID:24425866 doi:http://dx.doi.org/10.1074/jbc.M113.545566
