The Redox Couple of the Cytochrome \u3cem\u3ec\u3c/em\u3e Cyanide Complex: The Contribution of Heme Iron Ligation to the Structural Stability, Chemical Reactivity, and Physiological Behavior of Horse Cytochrome \u3cem\u3ec\u3c/em\u3e

Contrary to most heme proteins, ferrous cytochrome c does not bind ligands such as cyanide and CO. In order to quantify this observation, the redox potential of the ferric/ferrous cytochrome c–cyanide redox couple was determined for the first time by cyclic voltammetry. Its E0′ was −240 mV versus SHE, equivalent to −23.2 kJ/mol. The entropy of reaction for the reduction of the cyanide complex was also determined. From a thermodynamic cycle that included this new value for the cyt c cyanide complex E0′, the binding constant of cyanide to the reduced protein was estimated to be 4.7 × 10−3 LM−1 or 13.4 kJ/mol (3.2 kcal/mol), which is 48.1 kJ/mol (11.5 kcal/mol) less favorable than the binding of cyanide to ferricytochrome c. For coordination of cyanide to ferrocytochrome c, the entropy change was earlier experimentally evaluated as 92.4 Jmol−1K−1 (22.1 e.u.) at 25 K, and the enthalpy change for the same net reaction was calculated to be 41.0 kJ/mol (9.8 kcal/mol). By taking these results into account, it was discovered that the major obstacle to cyanide coordination to ferrocytochrome c is enthalpic, due to the greater compactness of the reduced molecule or, alternatively, to a lower rate of conformational fluctuation caused by solvation, electrostatic, and structural factors. The biophysical consequences of the large difference in the stabilities of the closed crevice structures are discussed

Direct Voltammetric Observation of Redox Driven Changes in Axial Coordination and Intramolecular Rearrangement of the Phenylalanine-82-Histidine Variant of Yeast Iso-1-cytochrome c

Direct square-wave and cyclic voltammetric electrochemical examination of the yeast iso-1-cytochrome c Phe82His/Cys102Ser variant revealed the intricacies of redox driven changes in axial coordination, concomitant with intramolecular rearrangement. Electrochemical methods are ideally suited for such a redox study, since they provide a direct and quantitative visualization of specific dynamic events. For the iso-1-cytochrome c Phe82His/Cys102Ser variant, square-wave voltammetry showed that the primary species in the reduced state is the Met80-Fe2+-His18 coordination form, while in the oxidized state the His82-Fe3+-His18 form predominates. The addition or removal of an electron to the appropriate form of this variant serves as a switch to a new molecular form of the cytochrome. Using the 2 × 2 electrochemical mechanism, simulations were done for the cyclic voltammetry experiments at different scan rates. These, in turn, provided relative rate constants for the intramolecular rearrangement/ligand exchange and the equilibrium redox potentials of the participating coordination forms:  kb,AC = 17 s-1 for Met80-Fe3+-His18 → His82-Fe3+-His18 and kf,BD \u3e 10 s-1 for His82-Fe2+-His18 → Met80-Fe2+-His18; E0‘ = 247 mV for Met80-Fe3+/2+-His18 couple, E0‘ = 47 mV for His82-Fe3+/2+-His18 couple, and E0‘ = 176 mV for the cross-reaction couple, His82-Fe3+-His18 + e- → Met80-Fe2+-His18. Thermodynamic parameters, including the entropy of reaction, ΔS0‘Rxn, were determined for the net reduction/rearrangement reaction, His82-Fe3+-His18 + e- → Met80-Fe2+-His18, and compared to those for wild-type cytochrome, Met80-Fe3+-His18 + e- → Met80-Fe2+-His18. For the Phe82His variant mixed redox couple, ΔS0‘Rxn = −80 J/mol·K compared to ΔS0‘Rxn = −52 J/mol·K for the wild-type cyt c couple without rearrangement. Comparison of these entropies indicates that the oxidized His82-Fe3+-His18 form is highly disordered. It is proposed that this high level of disorder facilitates rapid rearrangement to Met80-Fe2+-His18 upon reduction

SCAR is a primary regulator of Arp2/3-dependent morphological events in Drosophila

The Arp2/3 complex and its activators, Scar/WAVE and Wiskott-Aldrich Syndrome protein (WASp), promote actin polymerization in vitro and have been proposed to influence cell shape and motility in vivo. We demonstrate that the Drosophila Scar homologue, SCAR, localizes to actin-rich structures and is required for normal cell morphology in multiple cell types throughout development. In particular, SCAR function is essential for cytoplasmic organization in the blastoderm, axon development in the central nervous system, egg chamber structure during oogenesis, and adult eye morphology. Highly similar developmental requirements are found for subunits of the Arp2/3 complex. In the blastoderm, SCAR and Arp2/3 mutations result in a reduction in the amount of cortical filamentous actin and the disruption of dynamically regulated actin structures. Remarkably, the single Drosophila WASp homologue, Wasp, is largely dispensable for these numerous Arp2/3-dependent functions, whereas SCAR does not contribute to cell fate decisions in which Wasp and Arp2/3 play an essential role. These results identify SCAR as a major component of Arp2/3-dependent cell morphology during Drosophila development and demonstrate that the Arp2/3 complex can govern distinct cell biological events in response to SCAR and Wasp regulation

Looking on the bright side: biased attention and the human serotonin transporter gene

Humans differ in terms of biased attention for emotional stimuli and these biases can confer differential resilience and vulnerability to emotional disorders. Selective processing of positive emotional information, for example, is associated with enhanced sociability and well-being while a bias for negative material is associated with neuroticism and anxiety. A tendency to selectively avoid negative material might also be associated with mental health and well-being. The neurobiological mechanisms underlying these cognitive phenotypes are currently unknown. Here we show for the first time that allelic variation in the promotor region of the serotonin transporter gene (5-HTTLPR) is associated with differential biases for positive and negative affective pictures. Individuals homozygous for the long allele (LL) showed a marked bias to selectively process positive affective material alongside selective avoidance of negative affective material. This potentially protective pattern was absent among individuals carrying the short allele (S or SL). Thus, allelic variation on a common genetic polymorphism was associated with the tendency to selectively process positive or negative information. The current study is important in demonstrating a genotype-related alteration in a well-established processing bias, which is a known risk factor in determining both resilience and vulnerability to emotional disorders

Electrochemistry of nanozeolite-immobilized cytochrome c in aqueous and nonaqueous solutions

peer-reviewedThe electrochemical properties of cytochrome c (cyt c) immobilized on multilayer nanozeolite-modified electrodes have been examined in aqueous and nonaqueous solutions. Layers of Linde type-L zeolites were assembled on indium tin oxide (ITO) glass electrodes followed by the adsorption of cyt c, primarily via electrostatic interactions, onto modified ITO electrodes. The heme protein displayed a quasi-reversible response in aqueous solution with a redox potential of +324 mV (vs NHE), and the surface coverage (Gamma*) increased linearly for the first four layers and then gave a nearly constant value of 200 pmol cm(-2). On immersion of the modified electrodes in 95% (v/v) nonaqueous solutions, the redox potential decreased significantly, a decrease that originated from changes in both the enthalpy and entropy of reduction. On reimmersion of the modified electrode in buffer, the faradic response immediately returned to its original value. These results demonstrate that nanozeolites are potential stable supports for redox proteins and enzymes.ACCEPTEDpeer-reviewe

Characterization of the Clinical and Immunologic Phenotype and Management of 157 Individuals with 56 Distinct Heterozygous NFKB1 Mutations

Background: An increasing number of NFKB1 variants are being identified in patients with heterogeneous immunologic phenotypes. Objective: To characterize the clinical and cellular phenotype as well as the management of patients with heterozygous NFKB1 mutations. Methods: In a worldwide collaborative effort, we evaluated 231 individuals harboring 105 distinct heterozygous NFKB1 variants. To provide evidence for pathogenicity, each variant was assessed in silico; in addition, 32 variants were assessed by functional in vitro testing of nuclear factor of kappa light polypeptide gene enhancer in B cells (NF-κB) signaling. Results: We classified 56 of the 105 distinct NFKB1 variants in 157 individuals from 68 unrelated families as pathogenic. Incomplete clinical penetrance (70%) and age-dependent severity of NFKB1-related phenotypes were observed. The phenotype included hypogammaglobulinemia (88.9%), reduced switched memory B cells (60.3%), and respiratory (83%) and gastrointestinal (28.6%) infections, thus characterizing the disorder as primary immunodeficiency. However, the high frequency of autoimmunity (57.4%), lymphoproliferation (52.4%), noninfectious enteropathy (23.1%), opportunistic infections (15.7%), autoinflammation (29.6%), and malignancy (16.8%) identified NF-κB1-related disease as an inborn error of immunity with immune dysregulation, rather than a mere primary immunodeficiency. Current treatment includes immunoglobulin replacement and immunosuppressive agents. Conclusions: We present a comprehensive clinical overview of the NF-κB1-related phenotype, which includes immunodeficiency, autoimmunity, autoinflammation, and cancer. Because of its multisystem involvement, clinicians from each and every medical discipline need to be made aware of this autosomal-dominant disease. Hematopoietic stem cell transplantation and NF-κB1 pathway-targeted therapeutic strategies should be considered in the future.info:eu-repo/semantics/publishedVersio