The Case for Enzymatic Competitive Metal Affinity Methods.
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ABSTRACT:
SUBMITTER: Reilley DJ
PROVIDER: S-EPMC8130888 | biostudies-literature | 2020 Feb
REPOSITORIES: biostudies-literature
Publications
The Case for Enzymatic Competitive Metal Affinity Methods.
Reilley David J DJ Hennefarth Matthew R MR Alexandrova Anastassia N AN
ACS catalysis 20200117 3
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Project description:Phosphopeptide enrichment from complicated peptide mixtures is an essential step for mass spectrometry-based phosphoproteomic studies to reduce sample complexity and ionization suppression effects. Typical methods for enriching phosphopeptides include immobilized metal affinity chromatography (IMAC) or titanium dioxide (TiO2) beads, which have selective affinity and can interact with phosphopeptides. In this study, the IMAC enrichment method was compared with the TiO2 enrichment method, using a multistep enrichment strategy from whole cell lysate, to evaluate their abilities to enrich for different types of phosphopeptides. The peptide-to-beads ratios were optimized for both IMAC and TiO2 beads. Both IMAC and TiO2 enrichments were performed for three rounds to enable the maximum extraction of phosphopeptides from the whole cell lysates. The phosphopeptides that are unique to IMAC enrichment, unique to TiO2 enrichment, and identified with both IMAC and TiO2 enrichment were analyzed for their characteristics. Both IMAC and TiO2 enriched similar amounts of phosphopeptides with comparable enrichment efficiency. However, phosphopeptides that are unique to IMAC enrichment showed a higher percentage of multiphosphopeptides as well as a higher percentage of longer, basic, and hydrophilic phosphopeptides. Also, the IMAC and TiO2 procedures clearly enriched phosphopeptides with different motifs. Finally, further enriching with two rounds of TiO2 from the supernatant after IMAC enrichment or further enriching with two rounds of IMAC from the supernatant TiO2 enrichment does not fully recover the phosphopeptides that are not identified with the corresponding multistep enrichment.
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2015-06-01 | GSE47916 | GEO
Project description:Abstract: Despite recent advances in instrumentation and analytical strategies for identification and quantitation of protein phosphorylation, methodologies to enrich the heterogeneous types of phosphopeptides are critical towards comprehensive mapping of the under-explored phosphoproteome. Taking advantage of the distinctive binding affinity of Ga3+ and Fe3+ towards phosphopeptides, we designed a tip-based metal-directed immobilized metal ion affinity (MD-IMAC) chromatography for sequential enrichment of phosphopeptides. On the analysis of Raji B cell, this sequential Ga3+-Fe3+-IMAC strategy demonstrated 1.5-3.5 fold superior phosphoproteomic coverage compared to the single IMAC (Fe3+, Ti4+, Ga3+ and Al3+). In addition, as high as 92% among the 6283 phosphopeptides was uniquely enriched by either 1st Ga3+-IMAC fraction (41%) or 2nd Fe3+-IMAC fraction (51%). The complementary property of Ga3+ and Fe3+ was further shown on the exclusively superior efficiency to enriched almost all the 1214 multiply phosphorylated peptides (99.4%) by 1st Ga3+-IMAC, while as low as 10% of 5069 monophosphorylated phosphopeptides was commonly enriched by both fractions. Application of our sequential Ga3+-Fe3+-IMAC approach to a human lung cancer tissue allowed the identification of 2560 unique phosphopeptides with only 8% overlapping. The fractionation ability was shown not only on the mono phosphopeptides and multiply phosphopeptides but also on the basic and acidic phosphopeptides; acidiphilic phosphorylation sites were predominately present in 1st Ga3+-IMAC (72%) and 85% Pro-directed and 79% basophilic phosphorylation sites were enriched by 2nd Fe3+-IMAC. Most interestingly, this strategy complementarily mapped different kinase substrate on the protein as well as site levels in multiple cellular pathways related to cancer invasion and metastasis of lung cancer ., Given the demonstrated fractionation ability, reproducibility, sensitivity and ease of tip preparation, we hope that this Ga3+-Fe3+-IMAC allow more comprehensive characterization of phosphoproteome in vitro and in vivo. Database search: The raw MS/MS data obtained by TripleTOF 5600 were processed using AB_SCIEX MS Data Converter with default parameters. All MS/MS files were analyzed using Mascot (Matrix Science, London, UK; version 2.3) against the SwissPort database (version 57.8) with the following constraints: an allowance for tryptic peptides of up to two missed cleavage sites, a fragment ion mass tolerance of 0.05 Da, and a parent ion tolerance of 10 ppm. Phosphorylation (S, T, Y) and oxidation (M) were selected as variable modifications. Searching on a randomized decoy database created by Mascot was required to evaluate the false discovery rate associated with protein identification. The false discovery rates with a Mascot score (p< 0.05) ranged between 0% and 1% in this study.
2014-01-29 | PXD000314 | Pride
Project description:Fluorine-19 NMR and hyperpolarization form a powerful combination for drug screening. Under a competitive equilibrium with a selected fluorinated reporter ligand, the dissociation constant (K(D)) of other ligands of interest is measurable using a single-scan Carr-Purcell-Meiboom-Gill (CPMG) experiment, without the need for a titration. This method is demonstrated by characterizing the binding of three ligands with different affinities for the serine protease trypsin. Monte Carlo simulations show that the highest accuracy is obtained when about one-half of the bound reporter ligand is displaced in the binding competition. Such conditions can be achieved over a wide range of affinities, allowing for rapid screening of non-fluorinated compounds when a single fluorinated ligand for the binding pocket of interest is known.
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Project description:The affinity constant, also known as the equilibrium constant, binding constant, equilibrium association constant, or the reciprocal value, the equilibrium dissociation constant (Kd), can be considered as one of the most important characteristics for any antibody-antigen pair. Many methods based on different technologies have been proposed and used to determine this value. However, since a very large number of publications and commercial datasheets do not include this information, significant obstacles in performing such measurements seem to exist. In other cases where such data are reported, the results have often proved to be unreliable. This situation may indicate that most of the technologies available today require a high level of expertise and effort that does not seem to be available in many laboratories. In this paper, we present a simple approach based on standard immunoassay technology that is easy and quick to perform. It relies on the effect that the molar IC50 approaches the Kd value in the case of infinitely small concentrations of the reagent concentrations. A two-dimensional dilution of the reagents leads to an asymptotic convergence to Kd. The approach has some similarity to the well-known checkerboard titration used for the optimization of immunoassays. A well-known antibody against the FLAG peptide, clone M2, was used as a model system and the results were compared with other methods. This approach could be used in any case where a competitive assay is available or can be developed. The determination of an affinity constant should belong to the crucial parameters in any quality control of antibody-related products and assays and should be mandatory in papers using immunochemical protocols.
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Project description:Protein kinases are prime targets for drug development due to their involvement in various cancers. However, selective inhibition of kinases, while avoiding off-target effects remains a significant challenge for the development of protein kinase inhibitors. Activity-based protein profiling (ABPP), in combination with pan-kinase activity-based probes (ABPs) and mass spectrometry-based proteomics, enables the identification of kinase drug targets. Here, we extend existing ABPP strategies for kinase profiling with a site-specific analysis, allowing for protein kinase inhibitor target engagement profiling with amino acid specificity. The site-specific approach involves highly efficient enrichment of ABP-labeled peptides, resulting in a less complex peptide matrix, straightforward data analysis, and the screening of over ∼100 kinase active sites in a single LC-MS analysis. The complementary use of both trypsin and pepsin in parallel to generate the ABP-labeled peptides considerably expanded the coverage of kinases and pinpoint the exact binding sites. Using the site-specific strategy to examine the on- and off-targets of the Ephrin receptor (Eph) B4 inhibitor NVP-BHG712 showed binding to EphA2 with an IC50 of 17 nM and EphB4 with an IC50 of 20 nM. Next to the known targets, EphA2 and EphB4, NVP-BHG712 bound to the discoidin domain-containing receptor 1 with an IC50 of 2.1 nM, suggesting that a discoidin domain-containing receptor 1-targeting regio-isomer of NVP-BHG712 was used. The promiscuity of XO44 toward ATP-binding pockets on nonkinase proteins facilitated the screening of additional off-target sites, revealing inosine-5'-monophosphate dehydrogenase 2 as a putative off-target. Expanding the search to other amino acids revealed that XO44, in addition to 745 lysines, also covalently linked 715 tyrosines, which significantly expands the competitive ABPP search space and highlights the added value of the site-specific method. Therefore, the presented approach, which can be fully automated with liquid handling platforms, provides a straightforward, valuable new approach for competitive site-specific kinase inhibitor target profiling.
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