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Institute
The epitope imprinting approach applies exposed peptides as templates to synthesize Molecularly Imprinted Polymers (MIPs) for the recognition of the parent protein. While generally the template protein binding to such MIPs is considered to occur via the epitope-shaped cavities, unspecific interactions of the analyte with non-imprinted polymer as well as the detection method used may add to the complexity and interpretation of the target rebinding. To get new insights on the effects governing the rebinding of analytes, we electrosynthesized two epitope-imprinted polymers using the N-terminal pentapeptide VHLTP-amide of human hemoglobin (HbA) as the template. MIPs were prepared either by single-step electrosynthesis of scopoletin/pentapeptide mixtures or electropolymerization was performed after chemisorption of the cysteine extended VHLTP peptide. Rebinding of the target peptide and the parent HbA protein to the MIP nanofilms was quantified by square wave voltammetry using a redox probe gating, surface enhanced infrared absorption spectroscopy, and atomic force microscopy. While binding of the pentapeptide shows large influence of the amino acid sequence, all three methods revealed strong non-specific binding of HbA to both polyscopoletin-based MIPs with even higher affinities than the target peptides.
In this work, a novel electrochemical molecularly imprinted polymer (MIP) sensor for the detection of the lipopeptide antibiotic Daptomycin (DAP) is presented which integrates gold decorated platinum nanoparticles (Au-Pt NPs) into the nanocomposite film. The sensor was prepared by electropolymerization of o-phenylenediamine (o-PD) in the presence of DAP using cyclic voltammetry. Cyclic voltammetry and differential pulse voltammetry were applied to follow the changes in the MIP-layer related to rebinding and removal of the target DAP by using the redox marker [Fe(CN)(6)](3-/4-). Under optimized operational conditions, the MIP/Au-Pt NPs/ GCE nanosensor exhibits a linear response in the range of 1-20 pM towards DAP. The limit of detection and limit of quantification were determined to be 0.161pM +/- 0.012 and 0.489pM +/- 0.012, respectively. The sensitivity towards the antibiotics Vancomycin and Erythromycin and the amino acids glycine and tryptophan was below 7 percent as compared with DAP. Moreover, the nanosensor was also successfully used for the detection of DAP in deproteinated human serum samples.
Natürliche Evolution hat geschaffenBiopolymereauf der Basis von Aminosäuren undNukleotidezeigt hohe chemische Selektivität und katalytische Kraft. Die molekulare Erkennung durch Antikörper und die katalytische Umwandlung der Substratmoleküle durch Enzyme findet in sogenannten Paratopen oder katalytischen Zentren des Makromoleküls statt, die typischerweise 10-15 Aminosäuren umfassen. Die konzertierte Wechselwirkung zwischen den Reaktionspartnern führt zu Affinitäten bis zu nanomolaren Konzentrationen für die Antigenbindung und nähert sich einer Million Umsätze pro Sekunde anEnzym-katalysierte Reaktionen.
We report on the redox behaviour of the microperoxidase-11 (MP-11) which has been electrostatically immobilized in a matrix of chitosan-embedded gold nanoparticles on the surface of a glassy carbon electrode. MP-11 contains a covalently bound heme c as the redox active group that exchanges electrons with the electrode via the gold nanoparticles. Electroactive surface concentration of MP-11 at high scan rate is between 350+/-50 pmol cm(-2), which reflects a multilayer process. The formal potential (E degrees') of MP-11 in the gold nanoparticles-chitosan film was estimated to be -(267.7+/-2.9) mV at pH 7.0. The heterogeneous electron transfer rate constant (k(s)) starts at 1.21 s(-1) and levels off at 6.45 s(-1) in the scan rate range from 0.1 to 2.0 V s(-1). Oxidation and reduction of MP-11 by hydrogen peroxide and superoxide, respectively have been coupled to the direct electron transfer of MP-11.
Binding of heme to the amyloid peptides A beta 40/42 is thought to be an initial step in the development of symptoms in the early stages of Alzheimer's disease by enhancing the intrinsic peroxidatic activity of heme. We found considerably higher acceleration of the reaction for the physiologically relevant neurotransmitters dopamine and serotonin than reported earlier for the artificial substrate 3,3',5,5'-tetramethylbenzidine (TMB). Thus, the binding of hemin to A beta peptides might play an even more crucial role in the early stages of Alzheimer's disease than deduced from these earlier results. To mimic complex formation, a new surface architecture has been developed: The interaction between the truncated amyloid peptide A beta 1-16 and hemin immobilized on an aminohexanethiol spacer on a gold electrode has been analyzed by cyclic voltammetry. The resulting complex has a redox pair with a 25 mV more cathodic formal potential than hemin alone.
Hybrid architectures which combine a MIP with an immobilized affinity ligand or a biocatalyst sum up the advantages of both components. In this paper, hybrid architectures combining a layer of a molecularly imprinted electropolymer with a mini-enzyme or a self-assembled monolayer will be presented. (i) Microperoxidase-11 (MP-11) catalyzed oxidation of the drug aminopyrine on a product-imprinted sublayer: The peroxide dependent conversion of the analyte aminopyrine takes place in the MP-11 containing layer on top of a product-imprinted electropolymer on the indicator electrode. The hierarchical architecture resulted in the elimination of interfering signals for ascorbic acid and uric acid. An advantage of the new hierarchical structure is the separation of MIP formation by electropolymerization and immobilization of the catalyst. In this way it was for the first time possible to integrate an enzyme with a MIP layer in a sensor configuration. This combination has the potential to be transferred to other enzymes, e.g. P450, opening the way to clinically important analytes. (ii) Epitope-imprinted poly-scopoletin layer for binding of the C-terminal peptide and cytochrome c (Cyt c): The MIP binds both the target peptide and the parent protein almost eight times stronger than the non-imprinted polymer with affinities in the lower micromolar range. Exchange of only one amino acid in the peptide decreases the binding by a factor of five. (iii) MUA-poly-scopoletin MIP for cytochrome c: Cyt c bound to the MIP covered gold electrode exhibits direct electron transfer with a redox potential and rate constant typical for the native protein. The MIP cover layer suppresses the displacement of the target protein by BSA or myoglobin. The combination of protein imprinted polymers with an efficient electron transfer is a new concept for characterizing electroactive proteins such as Cyt c. The competition with other proteins shows that the MIP binds its target Cyt c preferentially and that molecular shape and the charge of protein determine the binding of interfering proteins.
For the first time a molecularly imprinted polymer (MIP)-based sensor for tyrosinase is described. This sensor is based on the electropolymerization of scopoletin or o-phenylenediamine in the presence of tyrosinase from mushrooms, which has a high homology to the human enzyme. The template was removed either by treatment with proteinase Kor by alkaline treatment. The measuring signal was generated either by measuring the formation of a product by the target enzyme or by evaluation of the permeability of the redox marker ferricyanide. The o-phenylenediamine-based MIP sensor has a linear measuring range up to 50 nM of tyrosinase with a limit of detection of 3.97 nM (R 2 = 0.994) and shows good discrimination towards other proteins, e.g., bovine serum albumin and cytochrome c.
A nanohybrid consisting of poly(3-aminobenzenesulfonic acid-co-aniline) and multiwalled carbon nanotubes [MWCNT-P(ABS-A)]) on a gold electrode was used to immobilize the hexameric tyrosine-coordinated heme protein (HTHP). The enzyme showed direct electron transfer between the heme group of the protein and the nanostructured surface. Desorption of the noncovalently bound heme from the protein could be excluded by control measurements with adsorbed hemin on aminohexanthiol-modified electrodes. The nanostructuring and the optimised charge characteristics resulted in a higher protein coverage as compared with MUA/MU modified electrodes. The adsorbed enzyme shows catalytic activity for the cathodic H2O2 reduction and oxidation of NADH.