Cobalt(III) as a stable and inert mediator ion between NTA and His6-tagged proteins.
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ABSTRACT:
SUBMITTER: Wegner SV
PROVIDER: S-EPMC3798096 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:A new bis-nitrilotriacetic acid (NTA) chelate with catechol anchor was synthesized and immobilized on superparamagnetic iron oxide nanoparticles. When loaded with Ni(II), these bis-NTA-immobilized nanoparticles were shown to bind polyhistidine (His x 6-tagged) fusion proteins in their native, folded conformations that commercial microbeads failed to bind under identical conditions. Control experiments with a mono-NTA chelate immobilized on iron oxide nanoparticles indicate a similarly high affinity for His x 6-tagged native proteins, suggesting that the high density of the mono-NTA chelate presented by the nanoparticles allows the binding of the His x 6-tag to more than one Ni-NTA moiety on the surface. This study shows that the multivalency strategy can be utilized to enhance the binding of His x 6-tagged proteins in their native, folded conformations. We further demonstrated the selective purification of His x 6-tagged proteins from crude cell lysates by using the Ni(II)-loaded iron oxide nanoparticles. The present platform is capable of efficient purification of His x 6-tagged proteins that are expressed at low levels in mammalian cells. This work thus presents a novel nanoparticle-based high-capacity protein purification system with shorter incubation times, proportionally large washes, and significantly smaller elution volumes compared to commercially available microbeads.
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Project description:Silica surfaces modified with nitrilotriacetic acid (NTA)-polyethylene glycol (PEG) derivatives were used to immobilize hexahistidine-tagged green fluorescent protein (His6-GFP), biotin/streptavidin-AlexaFluor555 (His6-biotin/SA-AF), and gramicidin A-containing vesicles (His6-gA). Three types of surface-reactive PEG derivatives-NTA-PEG3400-Si(OMe)3, NTA-PEG3400-vinylsulfone, and mPEG5000-Si(OMe)3 (control)-were grafted onto silica and tested for their ability to capture His6-tag species via His6/Ni2+/NTA chelation. The composition and thicknesses of the PEG-modified surfaces were characterized using X-ray photoelectron spectroscopy, contact angle, and ellipsometry. Protein capture efficiencies of the NTA-PEG-grafted surfaces were evaluated by measuring fluorescence intensities of these surfaces after exposure to His6-tag species. XPS and ellipsometry data indicate that surface adsorption occurs via specific interactions between the His6-tag and the Ni2+/NTA-PEG-grafted surface. Protein immobilization was most effective for NTA-PEG3400-Si(OMe)3-modified surfaces, with maximal areal densities achieved at 45 pmol/cm2 for His6-GFP and 95 fmol/cm2 for His6-biotin/SA-AF. Lipid vesicles containing His6-gA in a 1:375 gA/lipid ratio could also be immobilized on Ni2+/NTA-PEG3400-Si(OMe)3-modified surfaces at 0.5 mM total lipid. Our results suggest that NTA-PEG-Si(OMe)3 conjugates may be useful tools for immobilizing His6-tag proteins on solid surfaces to produce protein-functionalized surfaces.
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Project description:We report the fabrication of transmission electron microscopy (TEM) grids bearing graphene oxide (GO) sheets that have been modified with N?, N?-dicarboxymethyllysine (NTA) and deactivating agents to block non-selective binding between GO-NTA sheets and non-target proteins. The resulting GO-NTA-coated grids with these improved antifouling properties were then used to isolate His6-T7 bacteriophage and His6-GroEL directly from cell lysates. To demonstrate the utility and simplified workflow enabled by these grids, we performed cryo-electron microscopy (cryo-EM) of His6-GroEL obtained from clarified E. coli lysates. Single particle analysis produced a 3D map with a gold standard resolution of 8.1?Å. We infer from these findings that TEM grids modified with GO-NTA are a useful tool that reduces background and improves both the speed and simplicity of biological sample preparation for high-resolution structure elucidation by cryo-EM.
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Project description:Monitoring lipid distribution and metabolism in cells and biological fluids poses many challenges because of the many molecular species and metabolic pathways that exist. This study describes the synthesis and study of molecules that contain an alkyne functional group as surrogates for natural lipids in cultured cells. Thus, hexadec-15-ynoic and hexadec-7-ynoic acids were readily incorporated into RAW 264.7 cells, principally as phosphocholine esters; the alkyne was used as a "tag" that could be transformed to a stable dicobalt-hexacarbonyl complex; and the complex could then be detected by HPLC/MS or HPLC/UV(349nm). The 349 nm absorbance of the cobalt complexes was used to provide qualitative and quantitative information about the distribution and cellular concentrations of the alkyne lipids. The alkyne group could also be used as an affinity tag for the lipids by a catch-and-release strategy on phosphine-coated silica beads. Lipid extracts were enriched in the tagged lipids in this way, making the approach of potential utility to study lipid transformations in cell culture. Both terminal alkynes and internal alkynes were used in this affinity "pull-down" strategy. This method facilitates measuring lipid species that might otherwise fall below limits of detection.
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Project description:We report the preparation and performance of TEM grids bearing stabilized nonfouling lipid monolayer coatings. These films contain NTA capture ligands of controllable areal density at the distal end of a flexible poly(ethylene glycol) 2000 (PEG2000) spacer to avoid preferred orientation of surface-bound histidine-tagged (His-tag) protein targets. Langmuir-Schaefer deposition at 30 mN/m of mixed monolayers containing two novel synthetic lipids-1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[(5-amido-1-carboxypentyl)iminodiacetic acid]polyethylene glycolamide 2000) (NTA-PEG2000-DSPE) and 1,2-(tricosa-10',12'-diynoyl)-sn-glycero-3-phosphoethanolamine-N-(methoxypolyethylene glycolamide 350) (mPEG350-DTPE)-in 1:99 and 5:95 molar ratios prior to treatment with a 5 min, 254 nm light exposure was used for grid fabrication. These conditions were designed to limit nonspecific protein adsorption onto the stabilized lipid coating by favoring the formation of a mPEG350 brush layer below a flexible, mushroom conformation of NTA-PEG2000 at low surface density to enable specific immobilization and random orientation of the protein target on the EM grid. These grids were then used to capture His6-T7 bacteriophage and RplL from cell lysates, as well as purified His8-green fluorescent protein (GFP) and nanodisc solubilized maltose transporter, His6-MalFGK2. Our findings indicate that TEM grid supported, polymerized NTA lipid monolayers are capable of capturing His-tag protein targets in a manner that controls their areal densities, while efficiently blocking nonspecific adsorption and limiting film degradation, even upon prolonged detergent exposure.
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