Understanding the retinal basis of vision across species

The vertebrate retina first evolved some 500 million years ago in ancestral marine chordates. Since then, the eyes of different species have been tuned to best support their unique visuoecological lifestyles. Visual specializations in eye designs, large-scale inhomogeneities across the retinal surface and local circuit motifs mean that all species' retinas are unique. Computational theories, such as the efficient coding hypothesis, have come a long way towards an explanation of the basic features of retinal organization and function; however, they cannot explain the full extent of retinal diversity within and across species. To build a truly general understanding of vertebrate vision and the retina's computational purpose, it is therefore important to more quantitatively relate different species' retinal functions to their specific natural environments and behavioural requirements. Ultimately, the goal of such efforts should be to build up to a more general theory of vision

Impact of heme to protein linkages in peroxidases on redox chemistry and catalysis

The mammalian peroxidases participate in host defence against infection, hormone synthesis and pathogenesis. The most striking feature of these heme enzymes is the existence of two covalent ester bonds between the prosthetic group and the protein in the functional, mature proteins. Myeloperoxidase is unique in having an additional vinyl-sulfonium bond. The impact of heme distortion and asymmetry on the spectral and enzymatic properties is discussed as is the role of the MPO-typical electron withdrawing sulfonium ion linkage in raising the reduction potential of its redox intermediatesand maintaining a rigid solvent network at the distal heme cavity

Intracellular catalase/peroxidase from the phytopathogenic rice blast fungus Magnaporthe grisea: expression analysis and biochemical characterization of the recombinant protein

Phytopathogenic fungi such as the rice blast fungus Magnaporthegrisea are unique in having two catalase/peroxidase (KatG)paralogues located either intracellularly (KatG1) or extracellularly(KatG2). The coding genes have recently been shownto derive from a lateral gene transfer from a (proteo)bacterialgenome followed by gene duplication and diversification. Here wedemonstrate thatKatG1 is expressed constitutively in M. grisea. Itis the first eukaryotic catalase/peroxidase to be expressed heterologouslyin Escherichia coli in high amounts, with high purity andwith almost 100% haem occupancy. Recombinant MagKatG1is an acidic, mainly homodimeric, oxidoreductase with a predominantfive-co-ordinated high-spin haem b. At 25◦C andpH 7.0, the E0 (standard reduction potential) of the Fe(III)/Fe(II)couple was found to be −186+−10 mV. It bound cyanidemonophasically with an apparent bimolecular rate constant of(9.0+−0.4)×105 M−1 · s−1 at pH 7.0 and at 25◦C and with aKd value of 1.5 μM. Its predominantly catalase activity wascharacterized by a pH optimum at 6.0 and kcat and Km valuesof 7010 s−1 and 4.8 mM respectively. In addition, it acts as aversatile peroxidase with a pH optimum in the range 5.0–5.5using both one-electron [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) o-dianisidine, pyrogallol or guaiacol] andtwo-electron (Br−, I− or ethanol) donors. Structure–functionrelationships are discussed with respect to data reported forprokaryotic KatGs, as is the physiological role of MagKatG1.Phylogenetic analysis suggests that (intracellular) MagKatG1 canbe regarded as a typical representative for catalase/peroxidase ofboth phytopathogenic and saprotrophic fungi

Redox thermodynamics of lactoperoxidase and eosinophil peroxidase

Eosinophil peroxidase (EPO) and lactoperoxidase (LPO) are important constituents of the innate immunesystem of mammals. These heme enzymes belong to the peroxidase-cyclooxygenase superfamily and catalyzethe oxidation of thiocyanate, bromide and nitrite to hypothiocyanate, hypobromous acid and nitrogendioxide that are toxic for invading pathogens. In order to gain a better understanding of the observeddifferences in substrate specificity and oxidation capacity in relation to heme and protein structure, acomprehensive spectro-electrochemical investigation was performed. The reduction potential (E0) ofthe Fe(III)/Fe(II) couple of EPO and LPO was determined to be 126 mV and 176 mV, respectively(25 C, pH 7.0). Variable temperature experiments show that EPO and LPO feature different reductionthermodynamics. In particular, reduction of ferric EPO is enthalpically and entropically disfavored,whereas in LPO the entropic term, which selectively stabilizes the oxidized form, prevails on the enthalpicterm that favors reduction of Fe(III). The data are discussed with respect to the architecture of theheme cavity and the substrate channel. Comparison with published data for myeloperoxidase demonstratesthe effect of heme to protein linkages and heme distortion on the redox chemistry of mammalianperoxidases and in consequence on the enzymatic properties of these physiologically importantoxidoreductases

Redox thermodynamics of the Fe3+/Fe2+ couple in wild type and mutated heme peroxidases

The thermodynamics of the one-electron reduction of the ferricheme in wild-type and mutated heme Synechocystis catalaseperoxidase and human myeloperoxidase were determined through spectro-electrochemical experiments. The data are interpreted in terms of ligand binding features, electrostatic effects and solvation properties of the heme environment

Influence of the Covalent Heme 12Protein Bonds on the RedoxThermodynamics of Human Myeloperoxidase

Myeloperoxidase (MPO) is the most abundant neutrophil enzyme and catalyzes predominantly the twoelectron oxidation of ubiquitous chloride to generate the potent bleaching hypochlorous acid, thus contributing to pathogen killing as well as inflammatory diseases. Its catalytic properties are closely related with unique posttranslational modifications of its prosthetic group. In MPO, modified heme b is covalently bound to the protein via two ester linkages and one sulfonium ion linkage with a strong impact on its(electronic) structure and biophysical and chemical properties.Here, the thermodynamics of the one-electron reduction of the ferric heme in wild-type recombinant MPO and variants withdisrupted heme 12protein bonds (M243V, E242Q, and D94V) have been investigated by thin-layer spectroelectrochemistry. Itturns out that neither the oligomeric structure nor the N-terminal extension in recombinant MPO modifies the peculiar positivereduction potential (E\ub0\u2032 = 0.001 V at 25 \ub0C and pH 7.0) or the enthalpy or entropy of the Fe(III) to Fe(II) reduction. Bycontrast, upon disruption of the MPO 12typical sulfonium ion linkage, the reduction potential is significantly lower ( 120.182 V).The M243V mutant has an enthalpically stabilized ferric state, whereas its ferrous form is entropically favored because of the loss of rigidity of the distal H-bonding network. Exchange of an adjacent ester bond (E242Q) induced similar but less pronouncedeffects (E\ub0\u2032 = 120.094 V), whereas in the D94V variant (E\ub0\u2032 = 120.060 V), formation of the ferrous state is entropically disfavored.These findings are discussed with respect to the chlorination and bromination activity of the wild-type protein and the mutants

Disruption of the H-bond network in the main access channel of catalase–peroxidasemodulates enthalpy and entropy of Fe(III) reduction

Catalase–peroxidases are the only heme peroxidases with substantial hydrogen peroxide dismutation 28activity. In order to understand the role of the redox chemistry in their bifunctional activity, catalatically- 29active and inactive mutant proteins have been probed in spectroelectrochemical experiments. In detail, wild- 30type KatG from Synechocystis has been compared with variants with (i) disrupted KatG-typical adduct 31(Trp122-Tyr249-Met275), (ii) mutation of the catalytic distal His123-Arg119 pair, and (iii) altered 32accessibility to the heme cavity (Asp152, Ser335) and modified charge at the substrate channel entrance 33(Glu253). A valuable insight into the mechanism of reduction potential (E°′) modulation in KatG has been 34obtained from the parameterization of the corresponding enthalpic and entropic components, determined 35from the analysis of the temperature dependence of E°′. Moreover, model structures of ferric and ferrous 36Synechocystis KatG have been computed and used as reference to analyze and discuss the experimental data. 37The results, discussed by reference to published resonance Raman data on the strength of the proximal iron- 38imidazole bond and catalytic properties, demonstrate that E°′ of the Fe(III)/Fe(II) couple is not strongly 39correlated with the bifunctional activity. Besides the importance of an intact Trp-Tyr-Met adduct, it is the 40architecture of the long and constricted main channel that distinguishes KatGs from monofunctional 41peroxidases. An ordered matrix of oriented water dipoles is important for H2O2 oxidation. Its disruption 42results in modification of enthalpic and entropic contributions to E°′ that reflect reduction-induced changes 43in polarity, electrostatics, continuity and accessibility of solvent to the metal center as well as alterations in 44solvent reorganization

INTERNET, GUERRA Y PAZ EN COLOMBIA: CONFLICTO, NARRATIVAS E IDENTIDADES

El texto presenta una síntesis del componente tecnológico de la investigación interinstitucional “Internet, guerra y paz en Colombia”. Para tal fin, se hace un seguimiento a las nociones de innovación tecnológica, su uso y la construcción de la paz. En primer lugar, se reconstruye la discusión en torno a Internet en tanto objeto de estudio; posteriormente, se hace énfasis en el uso como apropiación comunicativa del medio y, finalmente, se realizan algunas anotaciones en términos de la transformación de los espacios comunicativos públicos en relación con el conflicto armado