5vmm
From Proteopedia
Staphylococcus aureus IsdB bound to human hemoglobin
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. Publication Abstract from PubMedIsdB is a receptor on the surface of the bacterial pathogen Staphylococcus aureus that extracts heme from hemoglobin (Hb) to enable growth on Hb as a sole iron source. IsdB is critically important both for in vitro growth on Hb and in infection models and is also highly upregulated in blood, serum, and tissue infection models, indicating a key role of this receptor in bacterial virulence. However, structural information for IsdB is limited. We present here a crystal structure of a complex between human Hb and IsdB. In this complex, the alpha; subunits of Hb are refolded with the heme displaced to the interface with IsdB. We also observe that atypical residues of Hb, His58 and His89 of alphaHb, coordinate to the heme iron, which is poised for transfer into the heme-binding pocket of IsdB. Moreover, the porphyrin ring interacts with IsdB residues Tyr440 and Tyr444. Previously, Tyr440 was observed to coordinate heme-iron in an IsdB.heme complex structure. A Y440F/Y444F IsdB variant we produced was defective in heme transfer, yet formed a stable complex with Hb (Kd = 6 +/- 2 muM) in solution with spectroscopic features of the bis-His species observed in the crystal structure. Haptoglobin binds to a distinct site on Hb to inhibit heme transfer to IsdB and growth of S. aureus, and a ternary complex of IsdB.Hb.Hp was observed. We propose a model for IsdB heme transfer from Hb that involves unfolding of Hb and heme-iron ligand exchange. Structure-function analyses reveal key features in Staphylococcus aureus IsdB-associated unfolding of the heme-binding pocket of human hemoglobin.,Bowden CFM, Chan ACK, Li EJW, Arrieta AL, Eltis LD, Murphy MEP J Biol Chem. 2017 Nov 6. pii: jbc.M117.806562. doi: 10.1074/jbc.M117.806562. PMID:29109153[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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