Oligopeptide Complexes Research Articles

Fluorescent Gadolinium(III)‐Oligopeptide Complexes and Carbon Nanotube Composite as Dual Modality Anticancer Agents

AbstractIn search of non‐platinum based anticancer drugs, we have synthesized and characterized a new class of three gadolinium(III)‐oligopeptides [Gd(L1)2(NO3)2][NO3] (1, L1=l‐aspartyl(OMe)‐N‐boc‐l‐aspartyl‐l‐aspartyl (OMe)), [Gd(L2)2(NO3)2][NO3] (2, L2=N‐fmoc‐l‐arginyl‐(Pbf)‐glycyl‐l‐aspartyl(OMe)), [Gd(L3)(NO3)3] (3, L3=N‐fmoc‐l‐arginyl‐(Pbf)‐l‐arginyl(OMe) and a carbon nanotube composite, 1@CNT 4. The three oligopeptides, L1 – L3 were prepared in a novel synthetic route using tetramethyl benzotriazolyl uronium hexaflurophosphate (HBTU) as a peptide coupling reagent. Confocal microscopic analysis of the gadolinium(III)‐oligopeptides, 1, 2 and CNT composite, 1@CNT 4 indicate that they display white and green light emissions upon excitations at λ, 405 and 488 nm with characteristic patterns. The oligopeptides, L1 & L3 display in vitro anticancer activity on HeLa cells with IC50 values in one mM concentration whereas the IC50 of RGD‐based oligopeptide was found to be 1 μM. The IC50 of gadolinium(III)‐oligopeptide, 1 and the CNT composite, 4 were found to be 1 μM and 10 nM. The transmission electron microscopic investigation of the HeLa cells treated with the composite 4 confirm the cellular uptake and indicate the presence of CNTs in the cytoplasm and that CNTs appear like bullets carrying the gadolinium(III)‐triaspartate, 1.

Crystal structures of a bacterial dipeptidyl peptidase IV reveal a novel substrate recognition mechanism distinct from that of mammalian orthologues

Dipeptidyl peptidase IV (DPP IV, DPP4, or DAP IV) preferentially cleaves substrate peptides with Pro or Ala at the P1 position. The substrate recognition mechanism has been fully elucidated for mammalian DPP IV by crystal structure analyses but not for bacterial orthologues. Here, we report the crystal structures of a bacterial DPP IV (PmDAP IV) in its free form and in complexes with two kinds of dipeptides as well as with a non-peptidyl inhibitor at 1.90 to 2.47 Å resolution. Acyl-enzyme intermediates were observed for the dipeptide complexes of PmDAP IV, whereas tetrahedral intermediates were reported for the oligopeptide complexes of mammalian DPP IVs. This variation reflects the different structural environments of the active site Arg residues, which are involved in the recognition of a substrate carbonyl group, of mammalian and bacterial enzymes. A phylogenetic analysis revealed that PmDAP IV is a closer relative of dipeptidyl peptidases 8 and 9 (DPP8 and DPP9, DPP IV-family enzymes) than DPP IV. These results provide new insights into the substrate recognition mechanism of bacterial DAP IVs and may assist in the development of selective inhibitors for DAP IVs from pathogenic asaccharolytic bacteria, which utilise proteins or peptides as an energy source.

Water Microsolvation Can Switch the Binding Mode of Ni(II) with Small Peptides.

Ni(II) ions can be caged by surrounding peptide ligands in two basic binding patterns: the "iminol" (IM) binding pattern, where chelation occurs by deprotonated amide nitrogens, or the charge-solvated (CS) binding pattern, where chelation occurs by amide carbonyl oxygens. Gas-phase observation may clarify the factors affecting this choice in solution and in peptide and protein matrices. Infrared spectroscopic determination of gas-phase structures shows here how microsolvation by just one water molecule switches the balance of this choice from IM to CS for the Ni2+Gly3 complex, in contrast with the always-CS structure of the Ni2+Gly4 complex. Quantum-chemical calculations indicate that CS complexation is even more favored in the aqueous limit. Considering gas-phase conditions as comparable to low-pH solutions can reconcile this prediction with the common observation of IM-type binding in solutions at higher pH. This is likely the first gas-phase observation of solvation-induced IM-to-CS transition in oligopeptide complexes with doubly charged transition-metal ions.

Comparative analysis of different geroprotective methods

One hundred and ten patients of different ages have undergone a comparative analysis of the efficiency and safety of a number of geroprotective techniques, including the use of dry lead-carbonate baths, hyperbaric oxygenation, therapeutic massage, and reception of oligopeptide preparations containing complexes of lysyl-glutamyl-asparagin and glutamyl-asparagin-arginine complexes (Vezugen and Pinealon). The most pronounced positive impact on indicators of biological age was found during the combined use of these two oligopeptide complexes. The safest ones in terms of influence on a number of biochemical and immunological parameters and on the clinical state of patients were medical massage and oligopeptide preparations. The use of dry carbon dioxide baths and hyperbaric oxygenation, while having an undoubtedly positive influence on the indices of biological age, has a number of limitations and counterindications.

Biogenic Fenton-like Reaction Involvement in Cometabolic Degradation of Tetrabromobisphenol A by Pseudomonas sp. fz

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant (BFR) that has frequently been detected in various environmental compartments. Although TBBPA biotransformation has been observed under both aerobic and anaerobic conditions, knowledge of the detailed mechanism of direct aerobic TBBPA biodegradation still remains limited. In this study, the underlying mechanism of cometabolic degradation of TBBPA by Pseudomonas sp. fz under aerobic conditions was investigated. Two key degradation pathways (beta scission and debromination) were proposed based on triple quadrupole liquid chromatography-mass spectrometry (LC-MS) analysis. TBBPA degradation by strain fz was demonstrated to be an extracellular process associated with the low-molecular-mass component (LMMC). Moreover, LMMC was preliminarily identified as oligopeptides, mainly consisting of glycine, proline, and alanine in a 2:1:1 molar ratio. Quenching studies suggested the involvement of hydroxyl radicals ((•)OH) in extracellular TBBPA degradation. To the best of our knowledge, we provide the first evidence that TBBPA was degraded by a biogenic Fenton-like reaction mediated via extracellular H2O2 and Fe(II)-oligopeptide complexes by the genus Pseudomonas. This study provides a new insight into the fate and biodegradation of TBBPA and other organic pollutants in natural and artificial bioremediation environments.

Quantitative serine protease assays based on formation of copper(II)-oligopeptide complexes.

A quantitative protease assay based on the formation of a copper-oligopeptide complex is developed. In this assay, when a tripeptide GGH fragment is cleaved from an oligopeptide chain by serine proteases, the tripeptide quickly forms a pink GGH/Cu(2+) complex whose concentration can be determined quantitatively by using UV-Vis spectroscopy. Therefore, activities of serine proteases can be determined from the formation rate of the GGH/Cu(2+) complex. This principle can be used to detect the presence of serine protease in a real-time manner, or measure proteolytic activities of serine protease cleaving different oligopeptide substrates. For example, by using this assay, we demonstrate that trypsin, a model serine protease, is able to cleave two oligopeptides GGGGKGGH () and GGGGRGGH (). However, the specificity constant (kcat/Km) for is higher than that of (6.4 × 10(3) mM(-1) min(-1)vs. 1.3 × 10(3) mM(-1) min(-1)). This result shows that trypsin is more specific toward arginine (R) than lysine (K) in the oligopeptide sequence.

Peptide-tethered monodentate and chelating histidylidene metal complexes: synthesis and application in catalytic hydrosilylation

The Nδ,Nε-dimethylated histidinium salt (His*) was tethered to oligopeptides and metallated to form Ir(III) and Rh(I) NHC complexes. Peptide-based histidylidene complexes containing only alanine, Ala-Ala-His*-[M] and Ala-Ala-Ala-His*-[M] were synthesised ([M] = Rh(cod)Cl, Ir(Cp*)Cl2), as well as oligopeptide complexes featuring a potentially chelating methionine and tyrosine residue, Met-Ala-Ala-His*-Rh(cod)Cl and Tyr-Ala-Ala-His*-Rh(cod)Cl. Chelation of the methionine-containing histidylidene ligand was induced by halide abstraction from the rhodium centre, while tyrosine remained non-coordinating under identical conditions. High catalytic activities in hydrosilylation were achieved with all peptide-based rhodium complexes. The cationic S(Met),C(His*)-bidentate peptide rhodium catalyst outperformed the monodentate neutral peptide complexes and constitutes one of the most efficient rhodium carbene catalysts for hydrosilylation, providing new opportunities for the use of peptides as N-heterocyclic carbene ligands in catalysis.

Copper (II) Complexes with Ac-HXH-NHMe (X=Gly, Ala and Aib) Peptide Motifs: Influence of Increasing CH3 Groups at Cα of Residue X on the Coordination in Solution

The interaction of Cu(II) ion with small peptides has been an interesting subject to clarify the role of copper in detail. As various Cu(II)-oligopeptide complexes can also be good models for the active centers of metalloenzymes, complexes of tripeptide and tetrapeptides are frequently investigated instead of the complexes of large peptides. The histidine side-chains of various metalloproteins frequently take part in the copper(II) coordination. Accordingly, we studied the coordination of Cu(II) to the N and C terminal protected tripeptide ligands L(A) (Ac-HisGlyHis-NHMe), L(B) (Ac-HisAlaHis-NHMe) and L(C) (Ac-HisAibHis-NHMe) in aqueous solution potentiometrially in order to determine the effect of C(alpha) methyl groups at middle residue acid on the ligation of the backbone NH and also on histidine's N(im) of coordination. Species distribution curves indicates that in acidic pH, all three peptides behave as bidentate ligands and a macrochelate forms on the metal coordination with the two histidine imidazolyl N. This coordination remains unaffected with the +I effect of increasing CH(3) groups at C(alpha) of middle residue. In the pH range 4-8, the tridentate coordination from the peptide is seen in ligand L(A) and L(B) while it is absent in L(C) due to +I effect of two C(alpha) methyl groups at middle residue as they makes N-terminal NH deprotonation difficult in this pH range and it takes place along with C terminal NH and only 4N coordinated species formed at higher pH. These 4N (N(im), N(-), N(-), N(im)) coordinated species are formed by all the three ligands at higher pH values.

Effect of oligopeptides on gene expression: comparison of DNA/peptide and DNA/peptide/liposome complexes

Plasmid DNA is known to form complexes with a variety of cationic peptides and lipids, which have been explored as possible carriers for DNA transfection in mammalian cells. We synthesized oligopeptides consisting of nine amino acid residues including lysine (K), tryptophan (W), and cysteine (C), and also their symmetrical dimmers with a disulfide bond as possible carriers. The pDNA(pGL3)/oligopeptide complexes generally showed poor transfection efficiencies but little cytotoxicity for HeLa S3. The ternary system of pDNA/oligopeptide/liposome containing cationic liposomes formulated from the cholesterol derivative (DMB-Chol) and dioleoylphosphatidylethanolamine (DOPE) showed 10 4–10 5-fold greater effective gene expression (10 8–10 9 level, RLU/min/mg protein) than those of the corresponding pDNA/oligopeptide complexes. In the presence of 10% serum, the ternary complexes were maintained at 10 7 levels. The ethidium bromide exclusion studies showed the ternary complexes have much greater affinity to pDNA than the corresponding pDNA/oligopeptide complexes. Plasmid sensitivity against DNase I degradation showed that the ternary complexes were well protected from the digestion. Synthetic oligopeptides are active as potential enhancers for DOPE-containing cationic liposome-mediated transfection. These findings have implications for successful in vivo transfection.

Hydrophobic interactions in metalloporphyrin-peptide complexes.

Synthetic heme−oligopeptide complexes of coproporphyrin-I-atoiron(III) have been prepared in aqueous solution, and their equilibrium formation constants have been determined by spectrophotometric titration. The presence of hydrophobic residues flanking the coordinated histidine dramatically increase peptide binding to the heme by more than 20 kJ/mol.

Fluorescence study of some terbium–oligopeptide complexes in methanolic solution

This study concerned the use of lanthanide chelates to detect glycyl-leucyl-phenylalanine (GLF) and its homologues. Spectroscopic analysis of peptides without or with terbium complexation revealed the formation of (LF) 3(Tb) 2, (GF) 3(Tb) 2, (GLF) 3(Tb) 2 and (FL) 4Tb, (FG) 4Tb complexes with high stability constants in methanolic solutions (p K d>13). Lanthanide chelate emission displayed a large Stokes shift (>270 nm), which allowed Tb chelates of GLF and its derivatives to be used for detection purposes. However, this preliminary study indicated some important limitations associated with lanthanide chelation, such as high methanolic content.

How the α-hydroxymethylserine residue stabilizes oligopeptide complexes with nickel(II) and copper(II) ions

Potentiometric, spectroscopic and theoretical studies have shown that the α-hydroxymethylserine (HmS) residue is a very specific amino acid residue when inserted into a peptide sequence. The theoretical calculations as well as evaluated deprotonation microconstants indicated that in the HmS-HmS-His tripeptide the N-terminal ammonium group is more acidic than the imidazole nitrogen. The hydrogen bond formation between the N-terminal amino group and imidazole nitrogen stabilizes the cyclic conformation of the metal-free peptide. The unusual gain in the 4N complex stability in the copper(II) and nickel(II) complexes with HmS-HmS-His ligands seems to derive from the enhancement of the π-electron contribution to the metal–amide nitrogen bond.

ANIN VIVO,EX VIVOANDIN VITROCOMPARATIVE STUDY OF ACTIVITY OF COPPER OLIGOPEPTIDE COMPLEXESVSCu(II) IONS

The tetrapeptide-Cu(II) complex H-(l-His-Gly)2-OH/Cu(II), indicated as L-Cu(II), has been investigated, as compared to the Cu(II) inorganic salt CuSO4, for its antioxidative and anti-inflammatory properties under a panel of experimental conditions. Both inorganic and organic Cu(II) compounds showed comparable activitiesin vitroandex vivoby: (i) protecting, in a dose-dependent manner, rat brain homogenates from Fe(III)/ascorbate- or haemoglobin-induced lipid peroxidation; (ii) inhibiting the superoxide-mediated ferricytochromecreduction by activated macrophages. CuSO4and L-Cu(II) also exhibited similar anti-inflammatory effectsin vivoby reducing significantly the extent of carrageenan-induced edema in the rat paw. The activities of the two compounds diverged strikingly only in the xanthine/xanthine oxidase system at low phosphate buffer concentration. L-Cu(II) decreased the rate of NBT reduction by superoxide in a true SOD-like fashion without affecting urate production. Instead, Cu(II) ions caused the rapid xanthine oxidase inactivation thus inhibiting both urate and superoxide production; this effect might be ascribed to the superoxide-mediated generation of the strong oxidant Cu(III) and its interaction with the enzyme. The administration of Cu(II), whether complexed with linear oligopeptides or as an inorganic salt, to animals or tissue extracts, conferred protection against oxidation and ought, conceivably, to interact with endogenous biological molecules and form highly bioavailable complexes which serve, subsequently, as the real scavengers. Moreover, the claimed prominent scavenger activities of Cu(II)-oligopeptide complexes over inorganic copper ions could be realised only in very simplein vitrosystems through mechanisms which, although of biochemical interest, are unlikely to be of physiopathological significance.

Reactions of copper(II)-oligopeptide complexes with hydrogen peroxide: Effects of biological reductants

Cu(II) complexes with oligopeptides containing histidyl residue in the second or third position could scarcely activate hydrogen peroxide (H 2O 2), but they could activate H 2O 2 to yield hydroxyl radical ( ·OH) in the presence of biological reductants such as cysteine and ascorbic acid. Further, DNA single strand breakage was also observed during the reactions of Cu(II)-glycylglycylhistidylglycine (GGHG) with H 2O 2 in the presence of same biological reductants.

Activation of hydrogen peroxide by copper(II) complexes with some histidine-containing peptides and their SOD-like activities

The reactivities of copper(II) complexes with histidine-containing oligopeptides towards active oxygen species such as hydrogen peroxide (H 2O 2) and superoxide ion (O 2 −) were investigated by electron spin resonance (ESR)-spin trapping and thiobarbituric acid (TBA) methods. At physiological pH values, Cu(II) complexes with oligopeptides containing histidyl residue at the N-terminal could more easily activate H 2O 2 to yield hydroxyl radical (·OH) than other Cu(II)-oligopeptide complexes containing histidyl residue in the second or third position. Further, it was suggested that since all Cu(II)-oligopeptide complexes examined could scavenge O 2 −, these complexes have SOD-like activities.

SOD-like activity of complexes of nickel(II) ion with some biologically important peptides and their novel reactions with hydrogen peroxide

At physiological pH values, nickel(II) complexes of oligopeptides containing histidine in the third position can quench superoxide ion (O 2 −) more easily than other Ni(II)-oligopeptide complexes. Furthermore, it is evidenced that Ni(II) complexes of oligopeptides containing histidine in the third position can catalyze the disproportionation of hydrogen peroxide (H 2O 2) to yield O 2 −, detected by electron spin resonance (ESR) spin trapping and nitro blue tetrazolium (NBT) methods.

Electrochemistry of Cu(II)-peptide complexes containing histidine residues II. Anomalous current fluctuation in the reduction process of Cu(II)-GGH

The electrochemical behavior of a Cu(II)GGH solution with a mercury electrode has been investigated. Cu(II)GGH showed anomalous current-potential and current-time characteristics in the electrode processes at the mercury electrode, which are described as follows. (i) Periodical current fluctuations and subsequent sudden cessation of the fluctuation were observed in the potential step measurement. (ii) Periodical current fluctuations were observed in the drop-life of a dropping mercury electrode in the potential region where the polarographic maximum appeared. (iii) Cyclic voltammogram showed irregular current fluctuations and a reversed current peak in the cathodic and the anodic runs, respectively. (iv) The half-wave potential of Cu(II)GGH was fairly negative in comparison with that of other Cu(II)-oligopeptide complexes. All of these phenomena were proposed to relate to the adsorption and desorption behaviors of the reduction product of Cu(II)GGH. The differential equation was presented to simulate the periodicity observed in the potential step measurement and it is found that a relatively simplified equation well simulated the periodical phenomena.

Superoxide dismutase activity and novel reactions with hydrogen peroxide of histidine-containing nickel(II)-oligopeptide complexes and nickel(II)-induced structural changes in synthetic DNA

At physiologic pH values, histidine-containing nickel(II) oligopeptides reduced the flux of superoxide anion (O2-) generated in the hypoxanthine/xanthine oxidase system. The postulated involvement of the Ni(III)/Ni(II) redox couple in this apparent dismutation receives indirect support from electron-spin resonance data. These complexes also catalyzed the disproportionation of hydrogen peroxide, a process which generates active intermediates capable of hydroxylating p-nitrophenol and oxidizing uric acid to allantoin. An oxene moiety, namely [Nio]2+, is postulated as the active species in these H2O2-dependent reactions. Spectral analysis showed that monovalent, divalent and trivalent ions induced cooperative conformational changes in synthetic polydeoxynucleotides. For the nickel(II) ion, resistance to DNase-I activity clearly showed that an alternating G-C sequence is required for the observed transitions. It is concluded that the ability of nickel(II) peptide complexes to participate in active oxygen biochemistry suggests a possible role for nickel as a chemical promoter of cancer, whereas the capacity of the nickel(II) ion to induce conformational changes in DNA could, in principle, affect gene expression. Of course, the validity of both hypotheses require that the observed reactions be verified as biologically significant.

Kinetics of the acid dissociation of oligopeptide complexes of copper(II) and nickel(II): a study on general-acid catalysis with "noncoordinating" 2,6-lutidine type buffers

Etude cinetique de la protonation et de la deprotonation de complexes du cuivre (II) et du nickel (II) avec la triglycine et la tetraglycine. Activite catalytique de tampons non complexants a base de lutidine et de collidine

1H NMR red-ox titration of copper(II)-histidine and -oligopeptide complexes with L(+)-ascorbic acid

Cu(II) complexes with histidine and analogues and their interaction with the vitamin C red-ox system were studied by means of 1H NMR spectroscopy. It could be shown that the paramagnetic line broadening as well as the red-ox activity observed by NMR at pH 7 depend on the pKR value of the imidazole residue. A reaction scheme is proposed which describes the NMR red-ox titration of the histidine-copper complexes. The exceptional role of Gly-Gly-His as a model for the protein binding site of copper ions and as an anti-tumor agent in correlation with ascorbic acid is interpreted in terms of its binding capability and red-ox activity as seen by the NMR method.