Metal displacement and stoichiometry of protein-metal complexes under native conditions using capillary electrophoresis/mass spectrometry

Cu(II) complexes with peptides from FomA protein containing -His-Xaa-Yaa-Zaa-His and -His-His-motifs. ROS generation and DNA degradation

Mono- and dinuclear Cu(II) complexes with Ac-PTVHNEYH-NH₂ (L1) and Ac-NHHTLND-NH₂ (L2) peptides from FomA protein of Fusobacterium nucleatum were studied by potentiometry, spectroscopic methods (UV-Vis, CD, EPR) and MS technique. The dominant mononuclear complexes for L1 ligand are: CuHL (pH range 5.0-6.0) with 2N {2N_im}, CuH_-2L (pH range 8.0-8.5) and CuH_-3L species (above pH 9.0) with 4N {N_im, 3N^-} coordination modes. The complexes: CuH_-1L with 3N {2N_im, N^-}, CuH_-2L with 3N {N_im, 2N^-} and CuH_-3L with 4N {N_im, 3N^-} binding sites are proposed for the L2 ligand. Probably in the CuH_-2L complex for CuL2 system the second His residue in His-His sequence is bound to Cu(II) ion, while the first His residue may stabilize this complex by His-His and/or His-Cu(II) interactions. The dominant dinuclear Cu₂L1 complexes in the pH range 6.5-10.5 are: the Cu₂H_-4L and Cu₂H_-6L species with 3N{N_im, 2N^-}4N{N_im, 3N^-} and 4N{N_im, 3N^-}4N{N_im, 3N^-} binding sites, respectively. In the case of the Cu₂L2 complex in the pH range 7.2-10.5, the Cu₂H_-4L and Cu₂H_-7L species dominate with 2N{N_im, N^-}4N{N_im, 3N^-} and (Cu(OH)₄^2-4N{N_im, 3N^-}) coordination modes, respectively. The ability to generate reactive oxygen species (ROS) by uncomplexed Cu(II) ions, ligands and their complexes at pH 7.4 in the presence of hydrogen peroxide or ascorbic acid was studied. UV-Vis, luminescence, EPR spin trapping and gel electrophoresis methods were used. Both complexes produce higher level of ROS compared to those of their ligands. ROS produced by Cu(II) complexes are hydroxyl radical and singlet oxygen, which contribute to oxidative DNA cleavage.

Novel approach for the synthesis of a neutral and covalently bound capillary coating for capillary electrophoresis-mass spectrometry made from highly polar and pH-persistent N-acryloylamido ethoxyethanol

Statically adsorbed or covalently coupled capillary coatings are of crucial importance in capillary electrophoresis-mass spectrometry for the separation of peptides and proteins. So far, published coating strategies and commercially available coated capillaries have a limited pH-stability so that the analysis at strongly acidic pH is limited, or harsh rinsing procedures for biological sample analysis cannot be applied. We here present a capillary coating based on Si-C linkages to N-acryloylamido ethoxyethanol (AAEE) with a new synthetic strategy including LiAlH₄ surface reaction. We optimized the coating method with emphasis on stability and reproducibility applying harsh rinsing procedures (strong acid, strong base and organic solvent), using the electroosmotic mobility and separation efficiency of tryptic peptides as performance measure. Complete synthesis is performed in less than 2 days for up to 8 capillaries in parallel of more than 16 m total length. Intra- and inter-batch reproducibility were determined regarding electroosmotic mobility, separation efficiency and migration time precision in CE-MS separations of tryptically digested bovine serum albumin. Coating stability towards rinsing with strong acid (1 mol/L HCl), organic solvent (acetonitrile) and strong base (1 mol/L NaOH) was investigated. Outstanding performance was found for single capillaries. However, inter-capillary reproducibility is discussed critically. The new coating was successfully applied for reproducible CE-MS separation of large proteins in diluted serum, medium-sized peptides and small and highly charged polyamines in fish egg extracts using a very acidic background electrolyte containing 0.75 mol/L acetic acid and 0.25 mol/L formic acid (pH 2.2).

Stability of Cu(ii) complexes with FomA protein fragments containing two His residues in the peptide chain

The coordination process of Cu(ii) ions with FomA protein fragments ofFusobacterium nucleatumcontaining two histydyl residues was determined.

Hybridization of Metal Nanoparticles with Metal-Organic Frameworks Using Protein as Amphiphilic Stabilizer

Here, a facile strategy is reported to efficiently hybridize metal nanoparticles (MNPs) with typical metal-organic frameworks (MOFs) of ZIF-8 (zeolitic imidazolate framework-8), which employs bovine serum albumin (BSA, a serum albumin protein derived from cows) as the amphiphilic stabilizer to increase the affinity of MNP toward MOFs. For instance, the as-synthesized PdNPs/ZIF-8 composites with diameter from 100 to 200 nm always maintain well-defined crystalline structure, and the PdNPs with small size of ∼2 nm are well-dispersed in the crystal of MOFs without serious aggregations due to the BSA stabilizer. In Suzuki cross-coupling reactions of aryl halide, the PdNPs/ZIF-8 as catalysts have exhibited high activity and satisfied reusability owing to the use of BSA stabilizer as well as the fixing of MOFs matrixes. In addition, the strategy also can be extended to synthesize other kinds of MNPs/MOFs hybrid composites with tunable particle size, which brings more opportunity for functional MOFs hybrid materials.

High stability and biological activity of the copper(II) complexes of alloferon 1 analogues containing tryptophan

Copper(II) complex formation processes between the alloferon 1 (Allo1) (HGVSGHGQHGVHG) analogues where the tryptophan residue is introducing in the place His residue H1W, H6W, H9W and H12W have been studied by potentiometric, UV-visible, CD and EPR spectroscopic, and MS methods. For all analogues of alloferon 1 complex speciation have been obtained for a 1:1 metal-to-ligand molar ratio and 2:1 of H1W because of precipitation at higher (2:1, 3:1 and 4:1) ratios. At physiological pH7.4 and a 1:1 metal-to-ligand molar ratio the tryptophan analogues of alloferon 1 form the CuH_-1L and/or CuH_-2L complexes with the 4N binding mode. The introduction of tryptophan in place of histidine residues changes the distribution diagram of the complexes formed with the change of pH and their stability constants compared to the respective substituted alanine analogues of alloferon 1. The CuH_-1L, CuH_-2L and CuH_-3L complexes of the tryptophan analogues are more stable from 1 to 5 log units in comparison to those of the alanine analogues. This stabilization of the complexes may result from cation(Cu(II))-π and indole/imidazole ring interactions. The induction of apoptosis in vivo, in Tenebrio molitor cells by the ligands and their copper(II) complexes at pH7.4 was studied. The biological results show that copper(II) ions in vivo did not cause any apparent apoptotic features. The most active were the H12W peptide and Cu(II)-H12W complex formed at pH7.4.

Binding States of Protein-Metal Complexes in Cells

The identification of endogenous proteins as well as their binding to metal ions in living cells is determined by combining pulsed electrophoretic separations with nanoelectrospray ionization followed by mass spectrometric detection. This approach avoids problems resulting from the complicated cellular environment. In this manner, we demonstrate the rapid identification (300 ms or less) of intact proteins from living E. coli cells including the complexation of calmodulin with calcium ion. The latter showed different binding states from those observed in in vitro studies. These observations also reveal in vitro measurements do not necessarily represent the actual situation in living cells. We conclude that the attempted in situ measurement of intracellular proteins with minimal sampling processes should be preferred.

Screening of Small Intact Proteins by Capillary Electrophoresis Electrospray Ionization-Mass Spectrometry (CE-ESI-MS)

Capillary electrophoresis (CE) has been shown to be a suitable separation technique for complex samples. Combined with electrospray ionization-mass spectrometry (ESI-MS), it is a powerful tool offering the opportunity of high selectivity and sensitivity combined with the possibility to identify and characterize intact proteins. In this protocol, we demonstrate a screening method for intact proteins based on capillary zone electrophoresis (CZE) separation coupled with online mass spectrometric detection. In order to avoid protein-wall interactions, a neutral coated capillary is used to create a universal method for proteins with both low and high electrophoretic mobilities. In addition, we show the successful validation and application of this screening method for a set of eight standard proteins and the glycoprotein erythropoietin.

Dissecting ITC data of metal ions binding to ligands and proteins

BACKGROUND

ITC is a powerful technique that can reliably assess the thermodynamic underpinnings of a wide range of binding events. When metal ions are involved, complications arise in evaluating the data due to unavoidable solution chemistry that includes metal speciation and a variety of linked equilibria.

SCOPE OF REVIEW

This paper identifies these concerns, provides recommendations to avoid common mistakes, and guides the reader through the mathematical treatment of ITC data to arrive at a set of thermodynamic state functions that describe identical chemical events and, ideally, are independent of solution conditions. Further, common metal chromophores used in biological metal sensing studies are proposed as a robust system to determine unknown solution competition.

MAJOR CONCLUSIONS

Metal ions present several complications in ITC experiments. This review presents strategies to avoid these pitfalls and proposes and experimentally validates mathematical approaches to deconvolute complex equilibria that exist in these systems.

GENERAL SIGNIFICANCE

This review discusses the wide range of complications that exists in metal-based ITC experiments. It provides a starting point for scientists new to this field and articulates concerns that will help experienced researchers troubleshoot experiments.

Native Liquid Extraction Surface Analysis Mass Spectrometry: Analysis of Noncovalent Protein Complexes Directly from Dried Substrates

Liquid extraction surface analysis (LESA) mass spectrometry is a promising tool for the analysis of intact proteins from biological substrates. Here, we demonstrate native LESA mass spectrometry of noncovalent protein complexes of myoglobin and hemoglobin from a range of surfaces. Holomyoglobin, in which apomyoglobin is noncovalently bound to the prosthetic heme group, was observed following LESA mass spectrometry of myoglobin dried onto glass and polyvinylidene fluoride surfaces. Tetrameric hemoglobin [(αβ)2(4H)] was observed following LESA mass spectrometry of hemoglobin dried onto glass and polyvinylidene fluoride (PVDF) surfaces, and from dried blood spots (DBS) on filter paper. Heme-bound dimers and monomers were also observed. The 'contact' LESA approach was particularly suitable for the analysis of hemoglobin tetramers from DBS.

Copper(ii) complexes of terminally free alloferon mutants containing two histidyl binding sites inside peptide chain structure and stability

The characterization of Cu(ii) complexes with alloferon 1 mutants H1A/H12A, H1A/H9A and H1A/H6A by potentiometry, CD, UV-Vis and EPR spectroscopic techniques, and ESI-MS spectrometry is reported.

Recent advances in coupling capillary electrophoresis-based separation techniques to ESI and MALDI-MS

Coupling CE-based separation techniques to MS creates a powerful platform for analysis of a wide range of biomolecules from complex samples because it combines the high separation efficiency of CE and the sensitivity and selectivity of MS detection. ESI and MALDI, as the most common soft ionization techniques employed for CE and MS coupling, offer distinct advantages for biomolecular characterization. This review is focused primarily on technological advances in combining CE and chip-based CE with ESI and MALDI-MS detection in the past five years. Selected applications in the analyses of metabolites, peptides, and proteins with recently developed CE-MS platforms are also highlighted.

High-throughput capillary electrophoresis-mass spectrometry: from analysis of amino acids to analysis of protein complexes

Recent advances in capillary electrophoresis-mass spectrometry (CE-MS) interfacing using porous tip is leading to commercialization of CE-MS with a sheathless interface for the first time. The new sheathless interface in conjunction with CE capillary coatings using self-coating background electrolytes (BGE) has significantly simplified CE-MS analysis of complex mixtures. CE-MS, with its high separation efficiency, compound identification capability, and ability to rapidly separate compounds with a wide range of mass and charge while consuming only nanoliters of samples, has become a valuable analytical technique for the analysis of complex biological mixtures. These advances have allowed a single capillary to analyze a range of compounds including amino acids, their D/L enantiomers, protein digests, intact proteins, and protein complexes. With these capabilities, CE-MS is poised to become the multipurpose tool of separation scientists. More recently, an eight-capillary CE in conjunction with an 8-inlet mass spectrometry has allowed 8 CE-MS analyses to be performed concurrently, significantly increasing throughput.

Study of the electrical connection mechanism of sheathless interface for capillary electrophoresis-electrospray ionization-mass spectrometry

With the combination of high separation ability of capillary electrophoresis (CE) and strong identification ability of mass spectrometry (MS), CE/MS is becoming a powerful tool for polar and ionic analytes analysis. Different interfaces have been developed to enhance the sensitivity and reliability since the first introduction of CE/MS in 1987. A sheathless porous interface based on a new ions transferring electric connection technique was reported to be with high sensitivity and reliability. In this work, a series of optical and electrochemical experiments were designed to study the electric connection process. The results indicated that closing CE electrical circuit and applying MS spray voltage were achieved by the small ions transferring through the interface porous wall. The new electric connection method significantly enhanced the sensitivity, resolution and stability of the CE/MS analysis. The interface was applied in CE/MS detection of morphine and 6-monoacetylmorphine in urine sample and showed an equal sensitivity to LC/MS. With the significant improvement of sensitivity and stability, the CE/MS with the new interface showed strong potential for the determination of low abundance analytes.

Capillary electrophoresis/mass spectrometry relevant to pharmaceutical and biotechnological applications

Advanced analytical techniques play a crucial role in the pharmaceutical and biotechnological field. In this context, capillary electrophoresis/mass spectrometry (CE/MS) has attracted attention due to efficient and selective separation in combination with powerful detection allowing identification and detailed characterization. Method developments and applications of CE/MS have been focused on questions not easily accessible by liquid chromatography/mass spectrometry (LC/MS) as the analysis of intact proteins, carbohydrates, and various small molecules, including peptides. Here, recent approaches and applications of CE/MS relevant to (bio)pharmaceuticals are reviewed and discussed to show actual developments and future prospects. Based on other reviews on related subjects covering large parts of previous works, the paper is focused on general ideas and contributions of the last 2 years; for the analysis of glycans, the period is extended back to 2006.

CE-MS for proteomics: Advances in interface development and application

Capillary electrophoresis-mass spectrometry (CE-MS) has emerged as a powerful technique for the analysis of proteins and peptides. Over the past few years, significant progress has been made in the development of novel and more effective interfaces for hyphenating CE to MS. This review provides an overview of these new interfacing techniques for coupling CE to MS, covering the scientific literature from January 2007 to December 2011. The potential of these new CE-MS interfacing techniques is demonstrated within the field of (clinical) proteomics, more specifically "bottom-up" proteomics, by showing examples of the analysis of various biological samples. The relevant papers on CE-MS for proteomics are comprehensively summarized in tables, including, e.g. information on sample type and pretreatment, interfacing and MS detection mode. Finally, general conclusions and future perspectives are provided.

High-throughput analysis using gated multi-inlet mass spectrometry

Gated multi-inlet mass spectrometry is introduced for high-throughput chemical analysis. In this design, multiple high-pressure liquid chromatography (HPLC) columns or capillary electrophoresis (CE) capillaries are attached to multiple electrosprayers (one for each column or capillary) that spray toward a gated multi-inlet time-of-flight mass spectrometer (TOF-MS). Although all of the sprayers are spraying continuously, only one inlet is exposed at any given time for a specific duration set by the MS data system. The gated multi-sprayer, multi-inlet design significantly enhances the performance of the multi-ESI, multi-inlet TOF-MS with minimal cost and reduces analysis time. The gated multi-sprayer, multi-inlet design was applied to the investigation of column-to-column reproducibility of multiple HPLCs using a peptide mixture and to the simultaneous analysis of four protein digests. In addition, it was applied to the analysis of peptide mixtures using eight CE capillaries. The gated multi-inlet MS has several advantages compared to our previous non-gated multi-inlet MS. For example, because only one inlet is open at one time, the original manufacturer's inlet inner diameter and pumping system can be used, which enhances the sensitivity of detection for each inlet and minimizes the manufacturing cost. In addition, the number of inlets can be increased as desired. The maximum number of liquid streams that can be concurrently analyzed is limited by: (1) the number of inlets, (2) the chromatographic (electrophoretic) peak width, and (3) how fast the gate can move from one position to the next.