3nl7 | pdb_00003nl7
Human Hemoglobin A mutant beta H63W carbonmonoxy-form
Structural highlights
DiseaseHBA_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] FunctionHBA_HUMAN Involved in oxygen transport from the lung to the various peripheral tissues. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedHis(E7) to Trp replacements in HbA lead to markedly biphasic bimolecular CO rebinding after laser photolysis. For isolated mutant subunits, the fraction of fast phase increases with increasing [CO], suggesting a competition between binding to an open conformation with an empty E7 channel and relaxation to blocked or closed, slowly reacting states. The rate of conformational relaxation of the open state is ~18,000 s-1 in alpha subunits and ~10-fold faster in beta subunits, ~175,000 s-1. Crystal structures were determined for tetrameric alpha(wt)beta(Trp63) HbCO, alpha(Trp58)beta(wt) deoxyHb, and Trp64 deoxy- and CO-Mb as controls. In Trp63(E7) betaCO, the indole side chain is located in the solvent interface, blocking entry into the E7 channel. Similar blocked Trp64(E7) conformations are observed in the mutant Mb crystal structures. In Trp58(E7) deoxy-alpha subunits, the indole side chain fills both the channel and the distal pocket, forming a completely closed state. The bimolecular rate constant for CO binding, k'CO, to the open conformations of both mutant Hb subunits is ~80-90 uM-1s-1, whereas k'CO for the completely closed states is 1000-fold slower, ~0.08 uM-1s-1. A transient intermediate with k'CO approximately 0.7 uM-1s-1 is observed after photolysis of Trp63(E7) betaCO subunits and indicates that the indole ring blocks the entrance to the E7 channel, as observed in the crystal structures of Trp(E7) deoxyMb and betaCO subunits. Thus, either blocking or completely filling the E7 channel dramatically slows bimolecular binding, providing strong evidence that the E7 channel is the major pathway (>/= 90%) for ligand entry in human hemoglobin. Blocking the gate to ligand entry in human hemoglobin.,Birukou I, Soman J, Olson JS J Biol Chem. 2010 Dec 29. PMID:21193395[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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