Copper(II) complexes with β-cyclodextrin–homocarnosine conjugates and their antioxidant activity

Peptides Derived from Angiogenin Regulate Cellular Copper Uptake

The angiogenin protein (ANG) is one of the most potent endogenous angiogenic factors. In this work we characterized by means of potentiometric, spectroscopic and voltammetric techniques, the copper complex species formed with peptide fragments derived from the N-terminal domain of the protein, encompassing the sequence 1-17 and having free amino, Ang1-17, or acetylated N-terminus group, AcAng1-17, so to explore the role of amino group in metal binding and cellular copper uptake. The obtained data show that amino group is the main copper anchoring site for Ang1-17. The affinity constant values, metal coordination geometry and complexes redox-potentials strongly depend, for both peptides, on the number of copper equivalents added. Confocal laser scanning microscope analysis on neuroblastoma cells showed that in the presence of one equivalent of copper ion, the free amino Ang1-17 increases cellular copper uptake while the acetylated AcAng1-17 strongly decreases the intracellular metal level. The activity of peptides was also compared to that of the protein normally present in the plasma (wtANG) as well as to the recombinant form (rANG) most commonly used in literature experiments. The two protein isoforms bind copper ions but with a different coordination environment. Confocal laser scanning microscope data showed that the wtANG induces a strong increase in intracellular copper compared to control while the rANG decreases the copper signal inside cells. These data demonstrate the relevance of copper complexes' geometry to modulate peptides' activity and show that wtANG, normally present in the plasma, can affect cellular copper uptake.

Nerve Growth Factor Peptides Bind Copper(II) with High Affinity: A Thermodynamic Approach to Unveil Overlooked Neurotrophin Roles

Nerve growth factor (NGF) is a protein essential to neurons survival, which interacts with its receptor as a non-covalent dimer. Peptides belonging to NGF N-terminal domain are able to mimic the activity of the whole protein. Such activity is affected by the presence of copper ions. The metal is released in the synaptic cleft where proteins, not yet identified, may bind and transfer to human copper transporter 1 (hCtr1), for copper uptake in neurons. The measurements of the stability constants of copper complexes formed by amyloid beta and hCtr1 peptide fragments suggest that beta-amyloid (Aβ) can perform this task. In this work, the stability constant values of copper complex species formed with the dimeric form of N-terminal domain, sequence 1–15 of the protein, were determined by means of potentiometric measurements. At physiological pH, NGF peptides bind one equivalent of copper ion with higher affinity of Aβ and lower than hCtr1 peptide fragments. Therefore, in the synaptic cleft, NGF may act as a potential copper chelating molecule, ionophore or chaperone for hCtr1 for metal uptake. Copper dyshomeostasis and mild acidic environment may modify the balance between metal, NGF, and Aβ, with consequences on the metal cellular uptake and therefore be among causes of the Alzheimer’s disease onset.

Exploring the Specificity of Rationally Designed Peptides Reconstituted from the Cell-Free Extract of Deinococcus radiodurans toward Mn(II) and Cu(II)

A series of five rationally designed decapeptides [DEHGTAVMLK (DP1), THMVLAKGED (DP2), GTAVMLKDEH (Term-DEH), TMVLDEHAKG (Mid-DEH), and DEHGGGGDEH (Bis-DEH)] have been studied for their interactions with Cu(II) and Mn(II) ions. The peptides, constructed including the most prevalent amino acid content found in the cell-free extract of Deinococcus radiodurans (DR), play a fundamental role in the antioxidant mechanism related to its exceptional radioresistance. Mn(II) ions, in complex with these peptides, are found to be an essential ingredient for the DR protection kit. In this work, a detailed characterization of Cu(II) systems was included, because Cu(II)–peptide complexes have also shown remarkable antioxidant properties. All peptides studied contain in their sequence coordinating residues that can bind effectively Mn(II) or Cu(II) ions with high affinity, such as Asp, Glu, and His. Using potentiometric techniques, NMR, EPR, UV–vis, and CD spectroscopies, ESI-MS spectrometry, and molecular model calculations, we explored the binding properties and coordination modes of all peptides toward the two metal ions, were able to make a metal affinity comparison for each metal system, and built a structural molecular model for the most stable Cu(II) and Mn(II) complexes in agreement with experimental evidence.

Five rationally designed decapeptides reconstituted from the cell-free extract of Deinococcus radiodurans have been precisely analyzed in terms of their coordination properties toward Mn(II) and Cu(II). The results provide new insight to enhance our understanding of the impact of metal complexes in the protection of the bacterium from various damaging agents such as ionizing radiation, ultraviolet radiation, and oxidative stress and novel information useful for exploiting this extraordinary ability in future biotechnological applications.

Focusing on the functional characterization of the anserinase from Oreochromis niloticus

Carnosine, anserine and homocarnosine are the three most representative compounds of the histidine dipeptides family, widely distributed in mammals in different amounts depending on the species and the tissue considered. Histidine dipeptides are mainly degraded by two different carnosinase homologues: a highly specific metal-ion dependent carnosinase (CN1) located in serum and brain and a non-specific cytosolic form (CN2). The hydrolysis of such dipeptides in prokaryotes and eukaryotes is also catalyzed by the anserinase (ANSN). Such naturally occurring dipeptides represent an interesting topic because they seem to have numerous biological roles such as potential neuroprotective and neurotransmitter functions in the brain and therefore ANSN results to be a very interesting target of study. We here report, for the first time, cloning, expression of ANSN from the fish Oreochromis niloticus both in a mammalian and in a prokaryotic system, in order to perform deep functional studies by enzymatic assays in the presence of different metals and substrates. Furthermore, by means of a mass spectrometry-based proteomic approach, we analysed protein sequence and the potential presence of post-translational modifications in the mammalian recombinant protein. Finally, a preliminary structural characterization was carried out on ANSN produced in Escherichia coli.

The Copper(II)-Assisted Connection between NGF and BDNF by Means of Nerve Growth Factor-Mimicking Short Peptides

Nerve growth factor (NGF) is a protein necessary for development and maintenance of the sympathetic and sensory nervous systems. We have previously shown that the NGF N-terminus peptide NGF(1-14) is sufficient to activate TrkA signaling pathways essential for neuronal survival and to induce an increase in brain-derived neurotrophic factor (BDNF) expression. Cu2+ ions played a critical role in the modulation of the biological activity of NGF(1-14). Using computational, spectroscopic, and biochemical techniques, here we report on the ability of a newly synthesized peptide named d-NGF(1-15), which is the dimeric form of NGF(1-14), to interact with TrkA. We found that d-NGF(1-15) interacts with the TrkA-D5 domain and induces the activation of its signaling pathways. Copper binding to d-NGF(1-15) stabilizes the secondary structure of the peptides, suggesting a strengthening of the noncovalent interactions that allow for the molecular recognition of D5 domain of TrkA and the activation of the signaling pathways. Intriguingly, the signaling cascade induced by the NGF peptides ultimately involves cAMP response element-binding protein (CREB) activation and an increase in BDNF protein level, in keeping with our previous result showing an increase of BDNF mRNA. All these promising connections can pave the way for developing interesting novel drugs for neurodegenerative diseases.

Carnosinases, their substrates and diseases

Carnosinases are Xaa-His dipeptidases that play diverse functions throughout all kingdoms of life. Human isoforms of carnosinase (CN1 and CN2) under appropriate conditions catalyze the hydrolysis of the dipeptides carnosine (β-alanyl-l-histidine) and homocarnosine (γ-aminobutyryl-l-histidine). Alterations of serum carnosinase (CN1) activity has been associated with several pathological conditions, such as neurological disorders, chronic diseases and cancer. For this reason the use of carnosinase levels as a biomarker in cerebrospinal fluid (CSF) has been questioned. The hydrolysis of imidazole-related dipeptides in prokaryotes and eukaryotes is also catalyzed by aminoacyl-histidine dipeptidases like PepD (EC 3.4.13.3), PepV (EC 3.4.13.19) and anserinase (EC 3.4.13.5). The review deals with the structure and function of this class of enzymes in physiological and pathological conditions. The main substrates of these enzymes, i.e., carnosine, homocarnosine and anserine (β-alanyl-3-methyl-l-histidine) will also be described.

Copper(II)-chelating homocarnosine glycoconjugate as a new multifunctional compound

Homocarnosine is an endogenous dipeptide distributed in cerebral regions and cerebrospinal fluid. Homocarnosine may serve as an antioxidant, free radical scavenger, neurotransmitter, buffering system and metal chelating agent, especially for copper(II) and zinc(II). The homeostasis of homocarnosine is regulated by carnosinases; the serum-circulating isoform of these metallodipeptidases partially hydrolyses homocarnosine in the blood. The enzyme activity is also inhibited by homocarnosine itself in a dose-dependent manner. We synthesized a new multifunctional homocarnosine derivative with trehalose, a disaccharide that possesses several beneficial properties, among which the inhibition of protein aggregation (i.e. Aβ amyloid and polyglutamine proteins) involved in widespread neurodegenerative disorders. We studied the copper(II) binding features of the new conjugate by means of potentiometric and spectroscopic techniques (UV-visible and circular dichroism) and the superoxide dismutase-like activity of the copper(II) complexes with homocarnosine and its trehalose conjugate was evaluated. The inhibitory effect of the new homocarnosine derivative on the carnosinase activity and its effects on Aβ aggregation were also investigated.

Selectively functionalized cyclodextrins and their metal complexes

Cyclodextrins (CDs) are cyclic oligomers of alpha-1,4-linked D-glucopyranose. Due to their unique structure, marked by a chiral and hydrophobic cavity, CDs have been extensively used as chiral selectors and drug delivery systems. The functionalization both improve the CD applications and widen their use in many other fields, such as molecular recognition and enzyme mimicking. Moreover, the functionalization highly increases the metal binding properties of the CDs. This critical review is a report of recent applications concerning the CD derivatives and their metal complexes. The metal ion assists the host-guest interaction often increasing the properties of CDs to act as chiral receptors. Furthermore, it can act as a catalytic center in the mimicking of metalloenzymes based on functionalized CDs (164 references).

Copper(II) complexes with an avian prion N-terminal region and their potential SOD-like activity

Potentiometric and spectroscopic (UV-Vis, CD and EPR) studies were carried out on copper(II) complexes with chicken prion protein N-terminal fragments, Ac-(PHNPGY)(4)-NH(2), and the mutated residue, Ac-(PHNPGF)(4)-NH(2), to assess the role of tyrosine in the copper coordination. Both thermodynamic and spectroscopic results indicate that chicken prion fragments are not able to bind more than two copper ions and only with the involvement of side chain tyrosine groups. The prevailing complex shows one copper ion bound to four imidazole nitrogen atoms in the 1:1 metal to ligand ratio systems. The superoxide dismutase (SOD)-like activity of copper(II) complexes with the avian peptides and mammal analogue, Ac-(PHGGGWGQ)(4)-NH(2), was also investigated by means of Pulse radiolysis. The copper(II) complexes with avian peptides do not display SOD-like activity, while very low activity has been detected for the copper(II) complexes with mammalian tetraoctarepeat.

Cellular stress response: a novel target for chemoprevention and nutritional neuroprotection in aging, neurodegenerative disorders and longevity

The predominant molecular symptom of aging is the accumulation of altered gene products. Moreover, several conditions including protein, lipid or glucose oxidation disrupt redox homeostasis and lead to accumulation of unfolded or misfolded proteins in the aging brain. Alzheimer's and Parkinson's diseases or Friedreich ataxia are neurological diseases sharing, as a common denominator, production of abnormal proteins, mitochondrial dysfunction and oxidative stress, which contribute to the pathogenesis of these so called "protein conformational diseases". The central nervous system has evolved the conserved mechanism of unfolded protein response to cope with the accumulation of misfolded proteins. As one of the main intracellular redox systems involved in neuroprotection, the vitagene system is emerging as a neurohormetic potential target for novel cytoprotective interventions. Vitagenes encode for cytoprotective heat shock proteins (Hsp) Hsp70 and heme oxygenase-1, as well as thioredoxin reductase and sirtuins. Nutritional studies show that ageing in animals can be significantly influenced by dietary restriction. Thus, the impact of dietary factors on health and longevity is an increasingly appreciated area of research. Reducing energy intake by controlled caloric restriction or intermittent fasting increases lifespan and protects various tissues against disease. Genetics has revealed that ageing may be controlled by changes in intracellular NAD/NADH ratio regulating sirtuin, a group of proteins linked to aging, metabolism and stress tolerance in several organisms. Recent findings suggest that several phytochemicals exhibit biphasic dose responses on cells with low doses activating signaling pathways that result in increased expression of vitagenes encoding survival proteins, as in the case of the Keap1/Nrf2/ARE pathway activated by curcumin and NAD/NADH-sirtuin-1 activated by resveratrol. Consistently, the neuroprotective roles of dietary antioxidants including curcumin, acetyl-L-carnitine and carnosine have been demonstrated through the activation of these redox-sensitive intracellular pathways. Although the notion that stress proteins are neuroprotective is broadly accepted, still much work needs to be done in order to associate neuroprotection with specific pattern of stress responses. In this review the importance of vitagenes in the cellular stress response and the potential use of dietary antioxidants in the prevention and treatment of neurodegenerative disorders is discussed.

Synthesis and antioxidant activity of new homocarnosine beta-cyclodextrin conjugates

Several in vitro and in vivo studies have suggested that carnosine (beta-alanil-L-histidine) and homocarnosine (beta-aminobutyril-L-histidine) can act as scavengers of reactive oxygen species. beta-Cyclodextrin was functionalized with homocarnosine, obtaining the following new bioconjugate isomers: 6(A)-[(4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}-4-oxobutyl)amino]-6(A)-deoxy-beta-cyclodextrin and (2(A)S,3(A)R)-3A-[(4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}-4-oxobutyl)amino]-3(A)-deoxy-beta-cyclodextrin. Pulse radiolysis investigations show that the beta-cyclodextrin homocarnosine bioconjugates are scavengers of (*)OH radicals because of the formation of stable imidazole-centered radicals and the scavenger ability of glucose molecules of the macrocycle. The ability of these new beta-cyclodextrin derivatives to inhibit the copper(II) driven LDL oxidation was determined in comparison with that displayed by the analogous carnosine derivatives. Both the beta-cyclodextrin carnosine isomers show a higher protective effect than that of free dipeptide and homocarnosine derivatives, bringing into light the role of the beta-CD cavity. The ability of these new beta-cyclodextrin derivatives to inhibit the copper(II) driven LDL oxidation was determined in comparison with that displayed by the analogous carnosine derivatives. Both the beta-cyclodextrin carnosine isomers show a higher protective effect than that of free dipeptide and homocarnosine derivatives, bringing into light the role of the beta-CD cavity.