Assessing Low Redox Stability of Myoglobin Relative to Rapid Hemin Loss from Hemoglobin

Bovine myoglobin (Mb) auto‐oxidized 11‐fold faster at pH 5.7 compared to bovine hemoglobin (Hb). Replacement of Ser(F7) in bovine Mb with positively charged or large apolar residues decreased auto‐oxidation rates (2‐ to 4‐fold) in comparison with wild‐type Mb (P < 0.05). However, the same substitutions increased hemin loss rate (15‐ to 28‐fold), indicating that hydrogen bonding between Ser(F7) and the heme‐7‐propionate is critical for stabilizing protoporphyrin in the globin. The anchoring of Ser(F7) to the heme‐7‐propionate in the proximal pocket of Mb is suggested to expose the distal pocket to solvent molecules that accelerate auto‐oxidation. The rate of hemin loss from metHb at pH 5.7 was 68‐fold faster compared to metMb. The ability of Ser(F7) and His(FG3) in Mb to form stabilizing contacts with the heme‐7‐propionate maintains hemin within the globin whereas Leu(F7) and Leu(FG3) of Hb cannot form stabilizing contacts which results in low hemin affinity. MetHb promoted lipid oxidation more effectively in washed muscle at pH 5.7 compared to metMb (P < 0.05). The greater ability of bovine metHb to promote lipid oxidation is likely due to its enhanced rate of hemin dissociation compared to bovine metMb.     

Enhancing the stability of microsomal cytochrome b5: a rational approach informed by comparative studies with the outer mitochondrial membrane isoform

The outer mitochondrial membrane isoform of mammalian cytochrome b5 (OM b5) is much less prone to lose heme than the microsomal isoform (Mc b5), with a conserved difference at position 71 (leucine versus serine) playing a major role. We replaced Ser71 in Mc b5 with Leu, with the prediction that it would retard heme loss by diminishing polypeptide expansion accompanying rupture of the histidine to iron bonds. The strategy was partially successful in that it slowed dissociation of heme from its less stable orientation in bMc b5 (B). Heme dissociation from orientation A was accelerated to a similar extent, however, apparently owing to increased binding pocket dynamic mobility related to steric strain. A second mutation (L32I) guided by results of previous comparative studies of Mc and OM b5s diminished the steric strain, but much greater relief was achieved by replacing heme with iron deuteroporphyrin IX (FeDPIX). Indeed, the stability of the Mc(S71L) b5 FeDPIX complex is similar to that of the FeDPIX complex of OM b5. The results suggest that maximizing heme binding pocket compactness in the apo state is a useful general strategy for increasing the stability of engineered or designed proteins.     

Erythrocytes: Central Actors in Multiple Scenes of Atherosclerosis

The development and progression of atherosclerosis (ATH) involves lipid accumulation, oxidative stress and both vascular and blood cell dysfunction. Erythrocytes, the main circulating cells in the body, exert determinant roles in the gas transport between tissues. Erythrocytes have long been considered as simple bystanders in cardiovascular diseases, including ATH. This review highlights recent knowledge concerning the role of erythrocytes being more than just passive gas carriers, as potent contributors to atherosclerotic plaque progression. Erythrocyte physiology and ATH pathology is first described. Then, a specific chapter delineates the numerous links between erythrocytes and atherogenesis. In particular, we discuss the impact of extravasated erythrocytes in plaque iron homeostasis with potential pathological consequences. Hyperglycaemia is recognised as a significant aggravating contributor to the development of ATH. Then, a special focus is made on glycoxidative modifications of erythrocytes and their role in ATH. This chapter includes recent data proposing glycoxidised erythrocytes as putative contributors to enhanced atherothrombosis in diabetic patients.     

Bismuth Sulfide Nanorods with Retractable Zinc Protoporphyrin Molecules for Suppressing Innate Antioxidant Defense System and Strengthening Phototherapeutic Effects

Bismuth (Bi)‐based nanomaterials (NMs) are widely used for computed tomography (CT) imaging guided photothermal therapy, however, the photodynamic property is hardly exhibited by these NMs due to the fast electron–hole recombination within their narrow bandgap. Herein, a sophisticated nanosystem is designed to endow bismuth sulfide (Bi₂S₃) nanorods (NRs) with potent photodynamic property. Zinc protoporphyrin IX (ZP) is linked to Bi₂S₃ NRs through a thermoresponsive polymer to form BPZP nanosystems. The stretching ZP could prebind to the active site of heme oxygenase‐1 overexpressed in cancer cells, suppressing the cellular antioxidant defense capability. Upon NIR laser irradiation, the heat released from Bi₂S₃ NRs could retract the polymer and drive ZP to the proximity of Bi₂S₃ NRs, facilitating an efficient electron–hole separation in ZP and Bi₂S₃ NRs, and leading to reactive oxygen species generation. In vitro and in vivo studies demonstrate the promising photodynamic property of BPZP, together with their photothermal and CT imaging performance.     

Immune Modulation by Inhibitors of the HO System

The heme oxygenase (HO) system involves three isoforms of this enzyme, HO-1, HO-2, and HO-3. The three of them display the same catalytic activity, oxidating the heme group to produce biliverdin, ferrous iron, and carbon monoxide (CO). HO-1 is the isoform most widely studied in proinflammatory diseases because treatments that overexpress this enzyme promote the generation of anti-inflammatory products. However, neonatal jaundice (hyperbilirubinemia) derived from HO overexpression led to the development of inhibitors, such as those based on metaloproto- and meso-porphyrins inhibitors with competitive activity. Further, non-competitive inhibitors have also been identified, such as synthetic and natural imidazole-dioxolane-based, small synthetic molecules, inhibitors of the enzyme regulation pathway, and genetic engineering using iRNA or CRISPR cas9. Despite most of the applications of the HO inhibitors being related to metabolic diseases, the beneficial effects of these molecules in immune-mediated diseases have also emerged. Different medical implications, including cancer, Alzheimer´s disease, and infections, are discussed in this article and as to how the selective inhibition of HO isoforms may contribute to the treatment of these ailments.     

Structural Insights into the Interaction of Heme with Protein Tyrosine Kinase JAK2**

Janus kinase 2 (JAK2) is the most important signal-transducing tyrosine kinase in erythropoietic precursor cells. Its malfunction drives several myeloproliferative disorders. Heme is a small metal-ion-carrying molecule that is incorporated into hemoglobin in erythroid precursor cells to transport oxygen. In addition, heme is a signaling molecule and regulator of various biochemical processes. Here, we show that heme exposure leads to hyperphosphorylation of JAK2 in a myeloid cancer cell line. Two peptides identified in JAK2 are heme-regulatory motifs and show low-micromolar affinities for heme. These peptides map to the kinase domain of JAK2, which is essential for downstream signaling. We suggest these motifs to be the interaction sites of heme with JAK2, which drive the heme-induced hyperphosphorylation. The results presented herein could facilitate the development of heme-related pharmacological tools to combat myeloproliferative disorders.