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
The solution structure of human adult carbonmonoxy hemoglobin (HbCO A) was refined using stereospecifically assigned methyl groups and residual dipolar couplings based on our previous nuclear magnetic resonance structure. The tertiary structures of individual chains were found to be very similar to the X-ray structures, while the quaternary structures in solution at low salt concentrations resembled the X-ray R structure more than the R2 structure. On the basis of chemical shift perturbation by inositol hexaphosphate (IHP) titration and docking, we identified five possible IHP binding sites in HbCO A. Amide-water proton exchange experiments demonstrated that alphaThr38 located in the alpha1beta2 interface and several loop regions in both alpha- and beta-chains were dynamic on the subsecond time scale. Side chain methyl dynamics revealed that methyl groups in the alpha1beta2 interface were dynamic, but those in the alpha1beta1 interface were quite rigid on the nanosecond to picosecond and millisecond to microsecond time scales. All the data strongly suggest a dynamic alpha1beta2 interface that allows conformational changes among different forms (like T, R, and R2) easily in solution. Binding of IHP to HbCO A induced small structural and dynamic changes in the alpha1beta2 interface and the regions around the hemes but did not increase the conformational entropy of HbCO A. The binding also caused conformational changes on the millisecond time scale, very likely arising from the relative motion of the alpha1beta1 dimer with respect to the alpha2beta2 dimer. Heterotropic effectors like IHP may change the oxygen affinity of Hb through modulating the relative motion of the two dimers and then further altering the structure of heme binding regions.
Solution structure and dynamics of human hemoglobin in the carbonmonoxy form.,Fan JS, Zheng Y, Choy WY, Simplaceanu V, Ho NT, Ho C, Yang D Biochemistry. 2013 Aug 27;52(34):5809-20. doi: 10.1021/bi4005683. Epub 2013 Aug, 15. PMID:23901897[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
- ↑ Fan JS, Zheng Y, Choy WY, Simplaceanu V, Ho NT, Ho C, Yang D. Solution structure and dynamics of human hemoglobin in the carbonmonoxy form. Biochemistry. 2013 Aug 27;52(34):5809-20. doi: 10.1021/bi4005683. Epub 2013 Aug, 15. PMID:23901897 doi:10.1021/bi4005683
