RESUMO
In the last two decades, the amyloid hypothesis, i.e., the abnormal accumulation of toxic Aß assemblies in the brain, has been considered the mainstream concept sustaining research in Alzheimer's Disease (AD). However, the course of cognitive decline and AD development better correlates with tau accumulation rather than amyloid peptide deposition. Moreover, all clinical trials of amyloid-targeting drug candidates have been unsuccessful, implicitly suggesting that the amyloid hypothesis needs significant amendments. Accumulating evidence supports the existence of a series of potentially dangerous relationships between Aß oligomeric species and tau protein in AD. However, the molecular determinants underlying pathogenic Aß/tau cross interactions are not fully understood. Here, we discuss the common features of Aß and tau molecules, with special emphasis on: (i) the critical role played by metal dyshomeostasis in promoting both Aß and tau aggregation and oxidative stress, in AD; (ii) the effects of lipid membranes on Aß and tau (co)-aggregation at the membrane interface; (iii) the potential of small peptide-based inhibitors of Aß and tau misfolding as therapeutic tools in AD. Although the molecular mechanism underlying the direct Aß/tau interaction remains largely unknown, the arguments discussed in this review may help reinforcing the current view of a synergistic Aß/tau molecular crosstalk in AD and stimulate further research to mechanism elucidation and next-generation AD therapeutics.
Assuntos
Doença de Alzheimer , Amiloidose , Doença de Alzheimer/metabolismo , Amiloide , Peptídeos beta-Amiloides/metabolismo , Proteínas Amiloidogênicas , Humanos , Íons , Lipídeos/uso terapêutico , Metais , Proteínas tau/metabolismoRESUMO
Currently, Alzheimer's Disease (AD) is a complex neurodegenerative condition, with limited therapeutic options. Several factors, like Amyloid ß (Aß) aggregation, tau protein hyperphosphorylation, bio-metals dyshomeostasis and oxidative stress contribute to AD pathogenesis. These pathogenic processes might occur in the aqueous phase but also on neuronal membranes. Thus, investigating the connection between Aß and biomembranes, becomes important for unveiling the molecular mechanism underlying Aß amyloidosis as a critical event in AD pathology. In this work, the interaction of two peptides, made up with hybrid sequences from Tau protein 9-16 (EVMEDHAG) or 26-33 (QGGYTMHQ) N-terminal domain and Aß16-20 (KLVFF) hydrophobic region, with full length Aß40 or Aß42 peptides is reported. The studied "chimera" peptides Ac-EVMEDHAGKLVFF-NH2 (τ9-16-KL) and Ac-QGGYTMHQKLVFF-NH2 (τ26-33-KL) are endowed with Aß recognition and metal ion interaction capabilities provided by the tau or Aß sequences, respectively. These peptides were characterized in previous study along with their metal dependent interaction and amyloidogenesis, either in the presence or absence of metal ion and artificial membranes made up with Total Lipid Brain Extract (TLBE) components, (Sciacca et al., 2020). In the present paper, the ability of the two peptides to inhibit Aß aggregation is studied using composite experimental conditions including aqueous solution, the presence of metal ions (Cu or Zn), the presence of lipid vesicles mimicking neuronal membranes as well as the co-presence of metals and TLBE artificial membranes. We used Thioflavine-T (ThT) fluorescence or MALDI-TOF spectrometry analysis of Aß limited proteolysis to respectively monitor the Aß aggregation kinetic or validation of the Aß interacting regions. We demonstrate that τ9-16-KL and τ26-33-KL peptides differently affect Aß aggregation kinetics, with the tau sequence playing a crucial role. The results are discussed in terms of chimera's peptides hydrophobicity and electrostatic driven interactions at the aqueous/membrane interface.
Assuntos
Peptídeos beta-Amiloides/química , Cobre/química , Fragmentos de Peptídeos/química , Peptídeos/química , Agregados Proteicos/fisiologia , Lipossomas Unilamelares/química , Zinco/química , Proteínas tau/química , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Humanos , Cinética , Peptídeos/metabolismo , Espectrometria de Fluorescência , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por MatrizRESUMO
Alzheimer's disease (AD) is a progressive neurodegenerative condition affecting people in the elderly. Targeting aggregation of ß-amyloid peptides (Aß) is considered a promising approach for the therapeutic treatment of the disease. Peptide based inhibitors of ß-amyloid fibrillation are emerging as safe drug candidates as well as interesting compounds for early diagnosis of AD. Peptide conjugation via covalent bond with functional moieties enables the resultant hybrid system to acquire desired functions. Here we report the synthesis, the structural characterization, and the Aß42 interaction of a p-amino-calix[4]arene derivative bearing a GPGKLVFF peptide pendant at the lower rim. We demonstrate that the p-amino-calix[4]arene-GPGKLVFF conjugate alters the Aß42 aggregation pathways by preventing Aß42's conformational transition from random coil to ß-sheet with concomitant changes of the aggregation kinetic profile as evidenced by circular dichroism (CD), thioflavin T (ThT), and dynamic light scattering (DLS) measurements, respectively. High resolution mass spectrometry (HR-MS) confirmed a direct interaction of the p-amino-calix[4]arene-GPGKLVFF conjugate with Aß42 monomer which provided insight into a possible working mechanism, whereas the alteration of the Aß42's fibrillary architecture, by the calix-peptide conjugate, was further validated by atomic force microscopy (AFM) imaging. Finally, the herein proposed compound was shown to be effective against Aß42 oligomers' toxicity in differentiated neuroblastoma cells, SH-SY5Y.
Assuntos
Doença de Alzheimer , Fragmentos de Peptídeos , Idoso , Peptídeos beta-Amiloides , Calixarenos , Humanos , Neurônios , FenóisRESUMO
Islet amyloid polypeptide (IAPP) is a hormone co-secreted with insulin and zinc from pancreatic ß-cells. To overcome the low solubility of human IAPP, we characterized zinc complexes species formed with 1)â a mutated form of rat-IAPP(1-37; R18 H) able to mimic the human IAPP, 2)â the r-IAPP(1-37) and the IAPP(1-8) fragment. Stoichiometry, speciation and coordination features of zinc(II) complexes were unveiled by ESI-MS, potentiometry and NMR measurements combined with DFT and free-energy simulations. Mononuclear species start to form around pHâ 6; Zn2+ binds both His18 and N-amino terminus in rat-IAPP(1-37; R18 H). The in silico study allows us to assess not only a structured turn compact domain in r-IAPP(1-37) and r-IAPP(1-37; R18 H) featured by a different free energy barrier for the transition from the compact to elongated conformation upon the coordination of Zn2+ , but also to bring into light a coordination shell further stabilized by noncovalent interactions.
Assuntos
Zinco/química , Amiloide , Animais , Simulação por Computador , Complexos de Coordenação , Humanos , Insulina , Polipeptídeo Amiloide das Ilhotas Pancreáticas , RatosRESUMO
The gold(III)-dithiocarbamate complex AuL12 (dibromo [ethyl-N-(dithiocarboxy-kS,kS')-N-methylglycinate] gold(III)), is endowed with promising in vitro/in vivo antitumor activity and toxicological profile. Here, we report our recent strategies to improve its water solubility and stability under physiological conditions along with our efforts for unravelling its tangled mechanism of action. We used three types of α-cyclodextrins (CDs), namely ß-CD, Me-ß-CD and HP-ß-CD to prepare aqueous solutions of AuL12. The ability of these natural oligosaccharide carriers to enhance water solubility of hydrophobic compounds, allowed drug stability of AuL12 to be investigated. Moreover, pharmacokinetic experiments were first carried out for a gold(III) coordination compound, after i.v. injection of the nanoformulation AuL12/HP-ß-CD to female mice. The gold content in the blood samples was detected at scheduled times by AAS (atomic absorption spectrometry) analysis, highlighting a fast biodistribution with a tß1/2 of few minutes and a slow escretion (tα1/2 of 14.3 h). The in vitro cytotoxic activity of AuL12 was compared with the AuL12/HP-ß-CD mixture against a panel of three human tumor cell lines (i.e., HeLa, KB and MCF7). Concerning the mechanism of action, we previously reported the proteasome-inhibitory activity of some our gold(III)-based compounds. In this work, we moved from the proteasome target to upstream of the important ubiquitin-proteasome pathway, testing the effects of AuL12 on the polyubiquitination reactions involving the Ub-activating (E1) and -conjugating (E2) enzymes.
Assuntos
Antineoplásicos/farmacologia , Ciclodextrinas/química , Ouro/farmacologia , Complexo de Endopeptidases do Proteassoma/metabolismo , Tiocarbamatos/farmacologia , Ubiquitina/antagonistas & inibidores , Animais , Antineoplásicos/síntese química , Antineoplásicos/química , Proliferação de Células/efeitos dos fármacos , Relação Dose-Resposta a Droga , Ensaios de Seleção de Medicamentos Antitumorais , Feminino , Ouro/química , Humanos , Camundongos , Camundongos Endogâmicos BALB C , Estrutura Molecular , Solubilidade , Relação Estrutura-Atividade , Tiocarbamatos/química , Distribuição Tecidual , Células Tumorais Cultivadas , Ubiquitina/metabolismo , Água/químicaRESUMO
Many biochemical pathways involving nerve growth factor (NGF), a neurotrophin with copper(II) binding abilities, are regulated by the ubiquitin (Ub) proteasome system. However, whether NGF binds Ub and the role played by copper(II) ions in modulating their interactions have not yet been investigated. Herein NMR spectroscopy, circular dichroism, ESI-MS, and titration calorimetry are employed to characterize the interactions of NGF with Ub. NGF1-14 , which is a short model peptide encompassing the first 14 N-terminal residues of NGF, binds the copper-binding regions of Ub (KD =8.6 10-5 m). Moreover, the peptide undergoes a random coil-polyproline typeâ II helix structural conversion upon binding to Ub. Notably, copper(II) ions inhibit NGF1-14 /Ub interactions. Further experiments performed with the full-length NGF confirmed the existence of a copper(II)-dependent association between Ub and NGF and indicated that the N-terminal domain of NGF was a valuable paradigm that recapitulated many traits of the full-length protein.
Assuntos
Cobre/química , Fator de Crescimento Neural/química , Peptídeos/química , Ubiquitina/química , Dicroísmo Circular , Humanos , Íons , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Ligação ProteicaRESUMO
Prion diseases are a group of neurodegenerative diseases based on the conformational conversion of the normal form of the prion protein (PrP(C)) to the disease-related scrapie isoform (PrP(Sc)). Copper(II) coordination to PrP(C) has attracted considerable interest for almost 20â years, mainly due to the possibility that such an interaction would be an important event for the physiological function of PrP(C). In this work, we report the copper(II) coordination features of the peptide fragment Ac(PEG11)3PrP(60-114) [Ac = acetyl] as a model for the whole N-terminus of the PrP(C) metal-binding domain. We studied the complexation properties of the peptide by means of potentiometric, UV/Vis, circular dichroism and electrospray ionisation mass spectrometry techniques. The results revealed that the preferred histidyl binding sites largely depend on the pH and copper(II)/peptide ratio. Formation of macrochelate species occurs up to a 2:1 metal/peptide ratio in the physiological pH range and simultaneously involves the histidyl residues present both inside and outside the octarepeat domain. However, at increased copper(II)/peptide ratios amide-bound species form, especially within the octarepeat domain. On the contrary, at basic pH the amide-bound species predominate at any copper/peptide ratio and are formed preferably with the binding sites of His96 and His111, which is similar to the metal-binding-affinity order observed in our previous studies.
Assuntos
Histamina/química , Peptídeos/química , Príons/química , Dicroísmo Circular , Cobre/química , Espectrometria de Massas , Ligação Proteica , Raios UltravioletaRESUMO
Pancreatic cancer (PC) is the fourth cause of cancer death in Western countries, the only chance for long term survival is an R0 surgical resection that is feasible in about 10%-20% of all cases. Five years cumulative survival is less than 5% and rises to 25% for radically resected patients. About 40% has locally advanced in PC either borderline resectable (BRPC) or unresectable locally advanced (LAPC). Since LAPC and BRPC have been recognized as a particular form of PC neoadjuvant therapy (NT) has increasingly became a valid treatment option. The aim of NT is to reach local control of disease but, also, it is recognized to convert about 40% of LAPC patients to R0 resectability, thus providing a significant improvement of prognosis for responding patients. Once R0 resection is achieved, survival is comparable to that of early stage PCs treated by upfront surgery. Thus it is crucial to look for a proper patient selection. Neoadjuvant strategies are multiples and include neoadjuvant chemotherapy (nCT), and the association of nCT with radiotherapy (nCRT) given as either a combination of a radio sensitizing drug as gemcitabine or capecitabine or and concomitant irradiation or as upfront nCT followed by nRT associated to a radio sensitizing drug. This latter seem to be most promising as it may select patients who do not go on disease progression during initial treatment and seem to have a better prognosis. The clinical relevance of nCRT may be enhanced by the application of higher active protocols as FOLFIRINOX.
Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Terapia Neoadjuvante/métodos , Pancreatectomia , Neoplasias Pancreáticas/terapia , Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Quimiorradioterapia Adjuvante , Quimioterapia Adjuvante , Humanos , Terapia Neoadjuvante/efeitos adversos , Terapia Neoadjuvante/mortalidade , Estadiamento de Neoplasias , Pancreatectomia/efeitos adversos , Pancreatectomia/mortalidade , Neoplasias Pancreáticas/mortalidade , Neoplasias Pancreáticas/patologia , Seleção de Pacientes , Radioterapia Adjuvante , Fatores de Risco , Fatores de Tempo , Resultado do TratamentoRESUMO
Gut dysmotility develops in individuals during and after recovering from infective acute gastroenteritis and it is apparently due to a direct effect of circulating lipopolysaccharides (LPS). This is an endotoxin with a prooxidant activity derived from gram-negative bacteria. Due to the lack of human models available so far, the mechanisms underlying LPS-induced gut dysmotility are, however, poorly investigated. In the present work long-term effects of LPS and their reversibility have been assessed by means of different analytical cytology methods on pure primary cultures of human colonic smooth muscle cells. We found that LPS triggered the following alterations: (i) a redox imbalance with profound changes of contractile microfilament network, and (ii) the induction of cell cycle progression with dedifferentiation from a contractile to a synthetic phenotype. These alterations persisted also after LPS removal. Importantly, two unrelated antioxidants, alpha-tocopherol and N-acetylcysteine, were able to reverse the cytopathic effects of LPS and to restore normal muscle cell function. The present data indicate that LPS is capable of triggering a persistent and long-term response that could contribute to muscle dysfunction occurring after an infective and related inflammatory burst and suggest a reappraisal of antioxidants in the management of postinfective motor disorders of the gut.
Assuntos
Acetilcisteína/farmacologia , Antioxidantes/farmacologia , Colo/citologia , Miócitos de Músculo Liso/efeitos dos fármacos , alfa-Tocoferol/farmacologia , Citoesqueleto de Actina/efeitos dos fármacos , Citoesqueleto de Actina/metabolismo , Adulto , Idoso , Idoso de 80 Anos ou mais , Ciclo Celular/efeitos dos fármacos , Forma Celular/efeitos dos fármacos , Células Cultivadas , Feminino , Fluoresceínas , Humanos , Interleucina-10/metabolismo , Interleucina-6/metabolismo , Lipopolissacarídeos/farmacologia , Masculino , Pessoa de Meia-Idade , Contração Muscular/efeitos dos fármacos , Miócitos de Músculo Liso/imunologia , Miócitos de Músculo Liso/metabolismo , Miócitos de Músculo Liso/fisiologia , NF-kappa B/metabolismo , Ouabaína/análogos & derivadosRESUMO
Mixed metal copper(II)-nickel(II) and copper(II)-zinc(II) complexes of four peptide fragments of human prion protein have been studied by potentiometric, UV-vis and circular dichroism spectroscopic techniques. One peptide contained three histidyl residues: HuPrP(84-114) with H85 inside and H96, H111 outside the octarepeat domain. The other three peptides contained two histidyl residues; H96 and H111 for HuPrP(91-115) and HuPrP(84-114)H85A while HuPrP(84-114)H96A contained the histidyl residues at positions 85 and 111. It was found that both histidines of the latter peptides can simultaneously bind copper(II) and nickel(II) ions and dinuclear mixed metal complexes can exist in slightly alkaline solution. One molecule of the peptide with three histidyl residues can bind two copper(II) and one nickel(II) ions. H85 and H111 were identified as the major copper(II) and H96 as the preferred nickel(II) binding sites in mixed metal species. The studies on the zinc(II)-PrP peptide binary systems revealed that zinc(II) ions can coordinate to the 31-mer PrP peptide fragments in the form of macrochelates with two or three coordinated imidazol-nitrogens but the low stability of these complexes cannot prevent the hydrolysis of the metal ion in slightly alkaline solution. These data provide further support for the outstanding affinity of copper(II) ions towards the peptide fragments of prion protein but the binding of nickel(II) can significantly modify the distribution of copper(II) among the available metal binding sites.
Assuntos
Cloretos/química , Complexos de Coordenação/química , Cobre/química , Histidina/análogos & derivados , Níquel/química , Fragmentos de Peptídeos/química , Príons/química , Compostos de Zinco/química , Sequência de Aminoácidos , Sítios de Ligação , Dicroísmo Circular , Complexos de Coordenação/síntese química , Histidina/química , Humanos , Concentração de Íons de Hidrogênio , Dados de Sequência Molecular , Ressonância Magnética Nuclear Biomolecular , Fragmentos de Peptídeos/síntese química , Polipeptídeo Hipofisário Ativador de Adenilato Ciclase/química , Precursores de Proteínas/química , Espectrofotometria UltravioletaRESUMO
The flexible N-terminal domain of the prion protein (PrP(c)) is believed to play a pivotal role in both trafficking of the protein through the cell membrane and its pathogenic conversion into the ß sheet-rich scrapie isoform (PrP(sc)). Unlike mammalian PrP(c), avian prion proteins are not known to undergo any pathogenic conformational conversions. Consequently, some critical advances in our understanding of the molecular mechanisms underlying prion pathogenesis are expected from comparative studies of the biophysical properties of the N-terminal domains of the two proteins. The present study addresses the role played by different environmental factors, i.e., copper(II), pH, and membrane-mimicking environments, in assisting the conformational preferences of huPrP60-91 and chPrP53-76, two soluble peptides encompassing the N-terminal copper(II) binding domains of the human and chicken prion proteins, respectively. Moreover, the membrane interactions of huPrP60-91, chPrP53-76, and their copper(II) complexes were evaluated by Trp fluorescence in conjunction with measurements of the variation in thermotropic properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles. Circular dichroism experiments revealed that huPrP60-91 adopts a predominant polyproline II conformation in aqueous solution that is destabilized at basic pH or in the presence of trifluoroethanol (TFE). Unlike anionic sodium dodecyl sulfate (SDS), which seems to stabilize the polyproline II conformation further, zwitterionic dodecylphosphocholine (DPC) micelles do not affect the peptide structure. On the contrary, copper(II) promptly promotes an increase in ß-turn-rich structures. Differential scanning calorimetry (DSC) and Trp fluorescence assays carried out on DPPC model membranes after incubation with huPrP60-91 showed a marked tendency of the peptide to slowly penetrate the lipid bilayer with a concomitant conformational transition toward an extended ß-sheet-like structure. Such an event, which was ascribed to the hydrophobic Trp side chain residues, was shown to also depend on the level of copper(II) occupancy along the peptide. Conversely, the CD spectra of chPrP53-76 aqueous solutions indicated the presence of a mixture of random-coil/ß-turn-like structures whose resulting equilibrium was influenced by SDS and copper(II) addition. Furthermore, chPrP53-76 did not exhibit any tendency to interact with model membranes in either the presence or absence of copper(II). The results reported here provide evidence of the different roles played by environmental factors in affecting the conformation and membrane activity of human and avian prion N-terminal domains.
Assuntos
Biomimética , Membrana Celular/metabolismo , Galinhas , Cobre/farmacologia , Príons/química , Príons/metabolismo , Sequências Repetitivas de Aminoácidos , 1,2-Dipalmitoilfosfatidilcolina/química , 1,2-Dipalmitoilfosfatidilcolina/metabolismo , Sequência de Aminoácidos , Animais , Varredura Diferencial de Calorimetria , Dicroísmo Circular , Humanos , Concentração de Íons de Hidrogênio , Metabolismo dos Lipídeos , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Conformação Proteica/efeitos dos fármacos , Solventes/química , Espectrometria de Fluorescência , Água/químicaRESUMO
Nickel(II) complexes of the peptide fragments of human prion protein containing histidyl residues both inside and outside the octarepeat domain have been studied by the combined application of potentiometric, UV-visible and circular dichroism spectroscopic methods. The imidazole-N donor atoms of histidyl residues are the exclusive metal binding sites below pH 7.5, but the formation of stable macrochelates was characteristic only for the peptide HuPrP(76-114) containing four histidyl residues. Yellow colored square planar complexes were obtained above pH 7.5-8 with the cooperative deprotonation of three amide nitrogens in the [N(im),N(-),N(-),N(-)] coordination mode. It was found that the peptides can bind as many nickel(II) ions as the number of independent histidyl residues. All data supported that the complex formation processes of nickel(II) are very similar to those of copper(II), but with a significantly reduced stability for nickel(II), which shifts the complex formation reactions into the slightly alkaline pH range. The formation of coordination isomers was characteristic of the mononuclear complexes with a significant preference for the nickel(II) binding at the histidyl sites outside the octarepeat domain. The results obtained for the two-histidine fragments of the protein, HuPrP(91-115), HuPrP(76-114)H85A and HuPrP(84-114)H96A, made it possible to compare the binding ability of the His96 and His111 sites. These data reveal a significant difference in the nickel(II) and copper(II) binding sites of the peptides: His96 was found to predominate almost completely for nickel(II) ions, while the opposite order, but with comparable concentrations, was reported for copper(II).
Assuntos
Histidina/química , Níquel/química , Peptídeos/química , Príons/química , Cobre/química , Humanos , Concentração de Íons de HidrogênioRESUMO
Spectroscopic (UV-Vis and EPR) and voltammetric studies have been carried out on the copper(II) complexes with the Ac-PEG11-(PHGGGWGQ)4-NH2 (L) polypeptide. In the ratios Cu : L 3 : 1 and 4 : 1, the two [Cu3(L)H(-6)] and [Cu4(L)H(-8)] complex species have been characterized at neutral pH values. All the copper atoms occupy similar coordination sites formed by imidazole, peptidic nitrogen atoms and carbonyl oxygen atoms in a square base pyramidal geometry. Voltammetric measurements on these systems point out the cooperativity in the electron transfer processes among the copper(II) sites during their reduction. NO interaction with these polynuclear copper species is characterized by the reduction of the copper sites through the formation of two different intermediate complex species. When an excess of the Ac-PEG11-(PHGGGWGQ)4-NH2 ligand is considered, frozen solution EPR parameters and UV-Vis spectroscopic data identify the [Cu(N(im))4]2+ chromophore, which does not interact with NO.
Assuntos
Cobre/química , Compostos Organometálicos/química , Peptídeos/química , Príons/química , Eletroquímica , Eletrodos , Espectroscopia de Ressonância de Spin Eletrônica , Ligantes , Óxido Nítrico/química , Espectrofotometria UltravioletaRESUMO
A 31-mer polypeptide, which encompasses residues 84-114 of human prion protein HuPrP(84-114) and contains three histidyl residues, namely one from the octarepeat (His85) and two histidyl residues from outside the octarepeat region (His96 and His111), and its mutants with two histidyl residues HuPrP(84-114)His85Ala, HuPrP(84-114) His96Ala, HuPrP(84-114)His111Ala and HuPrP(91-115) have been synthesised and their Cu2+ complexes studied by potentiometric and spectroscopic (UV/Vis, CD, EPR, ESI-MS) techniques. The results revealed a high Cu2+-binding affinity of all peptides, and the spectroscopic studies made it possible to clarify the coordination mode of the peptides in the different complex species. The imidazole nitrogen donor atoms of histidyl residues are the exclusive metal-binding sites below pH 5.5, and they have a preference for macrochelate structure formation. The deprotonation and metal-ion coordination of amide functions take place by increasing the pH; all of the histidines can be considered to be independent metal-binding sites in these species. As a consequence, di- and trinuclear complexes can be present even in equimolar samples of the metal ion and peptides, but the ratios of polynuclear species do not exceed the statistically expected ones; this excludes the possibility of cooperative Cu2+ binding. The species with a (N(im),N,N)-binding mode are favoured around pH 7, and their stability is enhanced by the macrochelation from another histidyl residue in the mononuclear complexes. The independence of the histidyl sites results in the existence of coordination isomers and the preference for metal binding follows the order of: His111>His96>His85. Deprotonation and metal-ion coordination of the third amide functions were detected in slightly alkaline solutions at each of the metal-binding sites; all had a (N(im),N,N,N)-coordination mode. Spectroscopic measurements also made it clear that the four lysyl amino groups of the peptides are not metal-binding sites in any cases.
Assuntos
Cobre/química , Histidina/química , Fragmentos de Peptídeos/química , Príons/química , Dicroísmo Circular , Espectroscopia de Ressonância de Spin Eletrônica , Humanos , Concentração de Íons de Hidrogênio , Fragmentos de Peptídeos/síntese química , Potenciometria , Receptores Histamínicos/químicaRESUMO
Histidine-containing peptide fragments of prion protein are efficient ligands to bind various transition metal ions and they have high selectivity in metal binding. The metal ion affinity follows the order: Pd(II)>>Cu(II)>>Ni(II)Zn(II)>Cd(II) approximately Co(II)>Mn(II). The high selectivity of metal binding is connected to the involvement of both imidazole and amide nitrogen atoms in metal binding for Pd(II), Cu(II) and Ni(II), while only the monodentate N(im)-coordination is possible with the other metal ions. The stoichiometry and binding mode of palladium(II) complexes show great variety depending on the metal ion to ligand ratio, pH and especially the presence of coordinating donor atoms in the side chains of peptide fragments. It is also clear from our data that the peptide fragments containing histidine outside the octarepeat (His96, His111 and His187) are more efficient ligands than the monomer peptide fragments of the octarepeat domain.