Anna Maria Santoro

Structural and kinetic characterization of native laccases from Pleurotus ostreatus, Rigidoporus lignosus, and Trametes trogii.

A comparative study has been performed on five native laccases purified from the three basidiomycete fungi Pleurotus ostreatus, Rigidoporus lignosus, and Trametes trogii to relate their different catalytic capacities to their structural properties. Spectroscopic absorption features and EPR spectra at various pH values of the five enzymes are very similar and typical of the blue oxidases. The analysis of the dependence of kinetic parameters on pH suggested that a histidine residue is involved in the binding of nonphenolic substrates, whereas both a histidine and an acidic residue may be involved in the binding of phenolic compounds. His and an Asp residue are indeed found at the bottom of a cavity which may be regarded as a suitable substrate channel for approaching to type 1 copper in the 3D homology models of the two laccases from Pleuorotus ostreatus (POXC and POXA1b) whose sequences are known.

Protective Effect of Carnosine During Nitrosative Stress in Astroglial Cell Cultures

Formation of nitric oxide by astrocytes has been suggested to contribute, via impairment of mitochondrial function, to the neurodegenerative process. Mitochondria under oxidative stress are thought to play a key role in various neurodegenerative disorders; therefore protection by antioxidants against oxidative stress to mitochondria may prove to be beneficial in delaying the onset or progression of these diseases. Carnosine has been recently proposed to act as antioxidant in vivo. In the present study, we demonstrate its neuroprotective effect in astrocytes exposed to LPS- and INFγ-induced nitrosative stress. Carnosine protected against nitric oxide-induced impairment of mitochondrial function. This effect was associated with decreased formation of oxidatively modified proteins and with decreased up-regulation oxidative stress-responsive genes, such as Hsp32, Hsp70 and mt-SOD. Our results sustain the possibility that carnosine might have anti-ageing effects to brain cells under pathophysiological conditions leading to degenerative damage, such as aging and neurodegenerative disorders.

A re-investigation of copper coordination in the octa-repeats region of the prion protein.

An aqueous solution spectroscopic (Vis and EPR) study of the copper(II) complexes with the Ac-HGGG-NH2 and Ac-PHGGGWGQ-NH2 polypeptides (generically designated as L) suggests square base pyramids ascribable to [Cu(L)H(-2)] complex species, which contain three nitrogen donor atoms, arising from imidazole and peptide groups, in the equatorial plane and for a pseudo-octahedral geometry in the case of [CuLH-3]- and [Cu(L)H-4]2- which have four nitrogen donor atoms in their equatorial plane. The coordination sphere of the copper complex in the [Cu(L)H(-2)] species, which is present at neutral pH values, is completed by two oxygen donor atoms. ESI-MS spectra ascertained that water molecules are not present in the coordination equatorial plane of this latter species, in comparison with other copper(II) complexes with ligands bearing nitrogen and oxygen donor atoms and surely having equatorial water molecules. This indicates the coordination of a carbonyl oxygen atom in the equatorial plane has to be invoked. However, no direct proof about the involvement of a carbonyl group oxygen donor atom apically linked to copper was obtained, due to the flexibility of these structures at room temperature. Additionally, the low A(ll) value leads one to consider another oxygen atom of a carbonyl group being involved in the apical bond to copper in a fast exchange fashion. This apical interaction, which may also involve a water molecule, is more pronounced in the Cu-Ac-HGGG-NH2 than in the analogous Cu-Ac-PHGGGWGQ-NH2 system, probably because of the presence of tryptophan and proline in the polypeptide sequence.

O2− scavenger properties of copper(II) complexes with diamino-diamide-type ligands

Abstract Copper(II) complexes with diamino-diamido-type ligands were tested as catalysts of O 2 − dismutation. ESR spectra of these systems showed that, in consequence of the O 2 − interaction, all the bis complexes of formula [Cu(L) 2 H −2 ] (where L = L-valylamide, L-phenylalanylamide, L-prolylamide) transformed into [Cu(L)H −1 (OH) 2 ] species. They also showed the highest scavenger as well as catalytic activity. The complex species formed after the interaction continued to show scavenger activity also. Stronger copper(II) complexes hardly interacted and showed scarce scavenger properties. In the series of [Cu(L′)H −2 ] complex species (where L′ = (S,S)N,N′-bis(phenylalanyl)-1,2-ethanediamine and -1,3-propanediamine, and (S,S)N,N′-bis(prolyl)-1,2-ethanediamine), the attempt to correlate catalytic activity with structural features revealed that a longer methylene chain could become a critical factor.

Comparison of three fungal laccases from Rigidoporus lignosus and Pleurotus ostreatus: correlation between conformation changes and catalytic activity.

The conformation changes in solution of three fungal laccases in different environmental conditions were examined by circular dichroism (CD) and electron paramagnetic resonance (EPR) spectroscopy. CD measurements indicate that the secondary structure of proteins depends slightly on the pH or ionic strength, though the presence of salt could interfere in the molecular recognition process between substrates and enzymes. The enzymes, however, are highly destabilized by prolonged exposure to low pH or high temperature. The observed unfolding of the proteins coincides with their inactivation and, in some cases, with precipitation. On the other hand, these conditions do not determine the disruption of the geometric arrangement of their metal centres, and this fact suggests that these centres represent the more stable core of the proteins.

Carnosine interaction with nitric oxide and astroglial cell protection

The neuropeptide carnosine (β‐amyloid peptide aggregation has been demonstrated. Carnosine protection against peroxynitrite damage is particularly relevant, but until now there has been no evidence of any direct interaction with nitric oxide. In this study we examined the protection that carnosine provides against nitric oxide (NO)–induced cell death in primary rat astroglial cell cultures treated with lipopolysaccharide (LPS) and interferon gamma (INFγ), a well‐known neurotoxic proinflammatory condition. A correlation was found between cell protection and NO free‐radical scavenging activity of carnosine. Moreover, by competitive spectrophotometric measurement and electrospray mass spectrometry analysis in cell‐free experiments, we demonstrated a direct interaction of the dipeptide with NO. A comparison of carnosine with its homologues or derivatives (homocarnosine and carcinine) as well as with its amino acid constituents (L‐histidine and β‐alanine) highlighted that only histidine showed significant scavenging activity. Therefore, carnosine shows direct NO‐trapping ability and may be a valuable multifunctional molecule in the treatment of neurodegenerative disorders.

Copper(II) complexes encapsulated in human red blood cells

Copper(II) complexes were encapsulated in human red blood cells in order to test their possible use as antioxidant drugs by virtue of their labile character. ESR spectroscopy was used to verify whether encapsulation in red blood cells leads to the modification of such complexes. With copper(II) complexes bound to dipeptides or tripeptides, an interaction with hemoglobin was found to be present, the hemoglobin having a strong coordinative site formed by four nitrogen donor atoms. Instead, with copper(II) complexes with TAD or PheANN3, which have the greatest stability. ESR spectra always showed the original species. Only the copper(II) complex with GHL gave rise to a complicated behavior, which contained signals from iron(III) species probably coming from oxidative processes. Encapsulation of all copper(II) complexes in erythrocytes caused a slight oxidative stress, compared to the unloaded and to the native cells. However, no significant differences were observed in the major metabolic properties (GSH, glycolytic rate, hexose monophosphate shunt, Ca(2+)-ATPase) of erythrocytes loaded with different copper(II) complexes, with the exception of methemoglobin levels, which were markedly increased in the case of [Cu(GHL)H-1] compared to [Cu(TAD)]. This latter finding suggests that methemoglobin formation can be affected by the type of complex used for encapsulation, depending on the direct interaction of the copper(II) complex with hemoglobin.

Copper(II) interaction with peptide fragments of histidine-proline-rich glycoprotein: Speciation, stability and binding details.

GHHPH is the peptide repeat present in histidine-proline rich glycoprotein (HPRG), a plasma glycoprotein involved in angiogenesis process. The copper(II) ions interaction with mono (Ac-GHHPHG-NH(2)) and its bis-repeat (Ac-GHHPHGHHPHG-NH(2)) was investigated by means of potentiometric and spectroscopic techniques. To single out the copper(II) coordination environments of different species formed with Ac-GHHPHG-NH(2), three single point mutated peptides were also synthesized and their ability to coordinate Cu(2+) investigated. Ac-GHHPHG-NH(2) binds Cu(2+) by the imidazole side chain and the amide nitrogen deprotonation that takes place towards the N-terminus. The bis-repeat is able to bind Cu(2+) more efficiently than Ac-GHHPHG-NH(2). This difference is not only due to the number of His residues in the sequence but also to the different binding sites. In fact, the comparison of the potentiometric and spectroscopic data of the copper(II) complexes with a bis-repeatPeg construct Ac-(GHHPHG)-Peg-(GHHPHG)-NH(2) and those of the metal complexes with Ac-HGHH-NH(2), indicates that the central HGHH amino acid sequence is the main copper(II) binding site.

New platinum(II) complexes of β-cyclodextrin diamine derivatives and their antitumor activity

The new platinum(II) complexes of beta-cyclodextrin functionalized at the primary position with ethylenediamine or with propylenediamine were synthesized and characterized by mass spectrometry, electronic spectrophotometry, and multinuclear NMR spectroscopy. Platinum(II) complexation makes the cavity more asymmetric. These complexes were tested in vitro for their cytotoxic activity. The relevance of the low activity observed regarding the interaction between the cell and the cyclodextrin cavity is discussed.

Functional Mimics of Cu, Zn- Superoxide Dismutase Enzymes

The purpose of this chapter is to summarize the knowledge on the ability of metal complexes to act as catalysts of the dismutation of superoxide radicals to hydrogen peroxide and dioxygen. The focus will be on the critical evaluation of this knowledge, and to suggest future developments. No attempt is made to be exhaustive in this very large body of literature [1, 2, 3, 4]. This field has grown so vast that discussing or even citing most of the important contributions is virtually impossible; therefore, important aspects might, and will, remain uncovered. Rather, the authors focus particularly on specific copper compounds, for which, to the best of our knowledge, the most recent review was published in 1989 [4].