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Metalloproteins under radical stress: an help from Raman spectroscopy
No full textRadical stress affecting proteins is a matter of interest in life sciences. Because of its enhanced gene expression in organisms exposed to reactive oxygen species and related processes such as inflammation, tumours or apoptosis, metallothioneins (MTs), low molecular weight metalloproteins (6-7 kDa), characterized by a high content in Cys and high heavy metal binding capacity, are of upmost importance in this field. Some of these MTs have shown to have the capacity to release sulfur-centered radicals capable of damaging lipids in a biomimetic model of the cell membrane when attacked by radical reductive [1,2].
Overall, the general structural properties that characterize all MTs are the formation of metal-thiolate clusters involving terminal and bridging cysteinyl thiolate groups. Recently, it has been shown that also exogenous ligands such as inorganic ions (i.e. sulfide or chloride ions) can participate in the coordination sphere of metals in MTs.
Some Zn-complexed MTs, representative of different MT families, enclosing plant MTs, have been analysed by Raman Spectroscopy [3]. Raman spectroscopy has resulted to be very useful in shedding light on the secondary structures eventually present in MTs and the ligands involved in metal coordination. The oxidation state of Cys residues and their participation in the metal chelation can be clearly defined (Figure 1), as well as the eventual involvement of His residues.
Some MTs were undergone to free radical stress and the protein degradation due to radical exposure was evaluated by Raman spectroscopy [1,2]. In fact, Raman spectrum can provide valuable information on both amino acid side chains (i.e. S-S, Tyr, Trp, Cys-Metal) and conformational changes (as example Figure 1). Experiments were carried out in both aqueous solutions and vesicle suspensions. Free radical generation, mimicking an endogenous radical stress, was obtained by gamma-irradiation of aqueous solutions. By changing the appropriate conditions of irradiation, a selection of the reacting radical species was carried out.
Protein structure and amino acid content resulted to play an important role in blocking the ready access of free radicals both to the sulfur-containing residues and the active site, so strongly affect both the radio-sensitivity of proteins. Thus, Raman can be an useful tool for providing information on the favourite sites of the radical attack and radical-induced modification in protein folding.
In conclusion, Raman spectroscopy, in coupling with analytical techniques, can be one of a very promising experimental strategies in the research on new hints on MTs.
References
[1] Torreggiani A, Chatgilialoglu C., Ferreri C, Melchiorre M., Atrian S, Capdevila M J Proteomics 92, 204 (2013)
[2] Torreggiani A, Domènech J, Orihuela R, Ferreri C, Atrian S, Capdevila M, Chatgilialoglu C. Chem Eur J 15 6015 (2009
The influence of solid-state molecular organization on the reaction paths of thiyl radicals
No full textElectron paramagnetic resonance (EPR) spectroscopy has been
employed to investigate the effect of solid-state molecular organization on the reaction of thiyl radicals with thiols. In an irradiated C18H37SH/thiourea clathrate, the conversion of thiyl to perthiyl radicals is substantial, due to the head-to-head arrangement of the reactants within the channels and the suppression of other possible competing reactions due to hindrance by the clathrate walls. The perthiyl radical was identified using EPR analysis of its molecular dynamics within the clathrate channels. Irradiated polyethylene film containing 30% C18H37SH afforded a negligible conversion of thiyl to perthiyl radicals because of the random distribution of reactants. These results suggest that in the absence of favorable structure-control effects, the reaction between RSC and RSH is unimportant with respect to other competing reactions.
Perthiyl radicals are also the major product in the vacuum
solid-state radiolysis of lysozyme. A proposal of the mechanism
involved in all cases is based on the equilibrium RSC+
RSHÐRSSC(H)R, followed by the irreversible conversion of the sulfuranyl radical to the perthiyl radical. As the equilibrium is
strongly shifted to the left, the intermediate sulfuranyl radicals
were not detected, but the lack of other competing reactions for
the thiyl radicals caused the formation of perthiyl radicals to
become the major path in the clathrate and in solid lysozyme radiolysis
Arachidonate Geometrical Isomers Generated by Thiyl Radicals: the Relationship with Trans Lipids Detected in Biological Samples.
No full text
Cis-trans isomerization of monounsaturated fatty acid residues in phospholipids by thiyl radicals
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cis-trans isomerization of polyunsaturated fatty acid residues in phospholipids catalysed by thiyl radicals
No full textArachidonate Geometrical Isomers Generated by Thiyl Radicals: the Relationship with Trans Lipids Detected in Biological Samples.
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