Preparation of Poly(pentafluorophenyl acrylate) Functionalized SiO2 Beads for Protein Purification
Summary
A protocol for the preparation of poly(pentafluorophenyl acrylate) (poly(PFPA)) grafted silica beads is presented. The poly(PFPA) functionalized surface is then immobilized with antibodies and used successfully for the protein separation through immunoprecipitation.
Abstract
We demonstrate a simple method to prepare poly(pentafluorophenyl acrylate) (poly(PFPA)) grafted silica beads for antibody immobilization and subsequent immunoprecipitation (IP) application. The poly(PFPA) grafted surface is prepared via a simple two-step process. In the first step, 3-aminopropyltrimethoxysilane (APTMS) is deposited as a linker molecule onto the silica surface. In the second step, poly(PFPA) homopolymer, synthesized via the reversible addition and fragmentation chain transfer (RAFT) polymerization, is grafted to the linker molecule through the exchange reaction between the pentafluorophenyl (PFP) units on the polymer and the amine groups on APTMS. The deposition of APTMS and poly(PFPA) on the silica particles are confirmed by X-ray photoelectron spectroscopy (XPS), as well as monitored by the particle size change measured via dynamic light scattering (DLS). To improve the surface hydrophilicity of the beads, partial substitution of poly(PFPA) with amine-functionalized poly(ethylene glycol) (amino-PEG) is also performed. The PEG-substituted poly(PFPA) grafted silica beads are then immobilized with antibodies for IP application. For demonstration, an antibody against protein kinase RNA-activated (PKR) is employed, and IP efficiency is determined by Western blotting. The analysis results show that the antibody immobilized beads can indeed be used to enrich PKR while non-specific protein interactions are minimal.
Introduction
Reactive polymer brushes have received much interest in recent years. They can be used to immobilize functional molecules on organic or inorganic materials to create activated surfaces with applications in areas such as detection and separation1,2,3,4,5. Among the reactive polymers reported, those containing pentafluorophenyl ester units are particularly useful due to their high reactivity with amines and resistance toward hydrolysis6. One such polymer is poly(PFPA), and it can be readily functionalized post-polymerization with molecules containing primary or secondary amines7,8,9,10. In one example, poly(PFPA) brushes were reacted with amino-spiropyrans to create light-responsive surfaces7.
The preparation of poly(PFPA) and its applications have been described in a number of previous publications6,7,8,9,10,11,12,13,14,15,16,17. In particular, Theato and co-workers reported the synthesis of poly(PFPA) brushes via both "grafting to" and "grafting from" methods7,8,10,11,12. In the "grafting to" approach, a poly(methylsilsesquioxane)-poly(pentafluorophenyl acrylate) (poly(MSSQ-PFPA)) hybrid polymer was synthesized8,10,11,12. The poly(MSSQ) component was able to form strong adhesion with a number of different organic and inorganic surfaces, thus allowing the poly(PFPA) component to form a brush layer on the coated material surface. In the "grafting from" approach, surface initiated reversible addition and fragmentation chain transfer (SI-RAFT) polymerization was employed to prepare poly(PFPA) brushes7. In this case, a surface immobilized chain transfer agent (SI-CTA) was first covalently attached to the substrate via silica-silane reaction. The immobilized SI-CTA then participated in the SI-RAFT polymerization of PFPA monomers, generating densely packed poly(PFPA) brushes with stable covalent linkage to the substrate.
By utilizing the poly(PFPA) brushes synthesized via SI-RAFT polymerization, we recently demonstrated the immobilization of antibodies on poly(PFPA) grafted silica particles and their subsequent application in protein purification18. The use of poly(PFPA) brushes for antibody immobilization was found to resolve a number of issues associated with current protein separation through IP. Conventional IP relies on the use of Protein A/G as a linker for antibody immobilization19,20,21. Since the use of Protein A/G allows the antibodies to be attached with a specific orientation, high target antigen recovery efficiency is achieved. However, the use of Protein A/G suffers from non-specific protein interaction as well as the loss of antibodies during protein recovery, both of which contribute to a high level of background noise. To resolve these shortcomings, direct crosslinking of the antibodies to a solid support has been explored22,23,24. The efficiency of such techniques is typically low due to the random orientation of the crosslinked antibodies. For the poly(PFPA) grafted substrate, the immobilization of antibodies is permanent, achieved through exchange reaction between PFP units and amine functionalities on antibodies. Although the antibody orientation is still random, the system benefits from having many reactive PFP sites, controllable by the degree of polymerization. Furthermore, we showed that by partial substitution of PFP units with amino-PEG, surface hydrophilicity can be tuned, further improving the protein recovery efficiency of the system18. Overall, the poly(PFPA) grafted silica particles were shown to be an effective alternative to traditional IP with reasonable efficiency as well as much cleaner background.
In this contribution, we report an alternative method to prepare poly(PFPA) grafted surface for antibody immobilization and IP application. In a simple two-step process, as illustrated in Figure 1, an APTMS linker molecule is first deposited onto the silica surface, then the poly(PFPA) polymer is covalently attached to the linker molecule through the reaction between the PFP units on the polymer and the amine functions on APTMS. This preparation method allows for the permanent crosslinking of poly(PFPA) to a substrate surface, but avoids the many complications associated with SI-CTA synthesis and SI-RAFT polymerization of poly(PFPA) brushes. Partial substitution of the PFP units with amino-PEG can still be performed, allowing fine-tuning of the polymer brush surface properties. We show the poly(PFPA) grafted silica beads thus prepared can be immobilized with antibodies and used for protein enrichment via IP. The detailed bead preparation procedure, antibody immobilization, and IP testing are documented in this article, for readers interested in seeking an alternative to conventional Protein A/G based IP.
Protocol
Representative Results
Discussion
The synthesis of poly(PFPA) grafted SiO2 beads is illustrated in Figure 1. By employing APTMS as a linker molecule, poly(PFPA) brushes covalently grafted to SiO2 substrate can be prepared via a simple two-step process. Although some of the PFP units are sacrificed for the reaction with APTMS, a large number of the PFP units are expected to remain available for later reaction with either amino-PEG or antibodies. The PFP groups are known to form low energy surfaces so pol…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
This work was supported by Agency for Defense Development (Grant No. UD170039ID).
Materials
| 2,2-Azobisisobutyronitrile, 99% | Daejung Chemicals | 1102-4405 | |
| Methyl alcohol for HPLC, 99.9% | Duksan Pure Chemicals | d62 | |
| Phenylmagnesium bromide solution 1.0 M in THF | Sigma-Aldrich | 331376 | |
| Carbon disulfide anhydrous, ≥99% | Sigma-Aldrich | 335266 | |
| Benzyl bromide, 98% | Sigma-Aldrich | B17905 | |
| Petroleum ether, 90% | Samchun Chemicals | P0220 | |
| Ethyl ether, 99% | Daejung Chemicals | 4025-4404 | |
| Magnesium sulfate anhydrous, powder, 99% | Daejung Chemicals | 5514-4405 | |
| Pentafluorophenyl acrylate | Santa Cruz Biotechnology | sc-264001 | contains inhibitor |
| Aluminium oxide, activated, basic, Brockmann I | Sigma-Aldrich | 199443 | |
| Sodium Chloride (NaCl) | Daejung Chemicals | 7548-4400 | |
| Anisole anhydrous, 99.7% | Sigma-Aldrich | 296295 | |
| Silica nanoparticle | Microparticles GmbH | SiO2-R-0.7 | 5% w/v aqueous suspension |
| 3-Aminopropyltrimethoxysilane, >96.0% | Tokyo Chemical Industry | T1255 | |
| Dimethyl sulfoxide for HPLC, ≥99.7% | Sigma-Aldrich | 34869 | |
| Amino-terminated poly(ethylene glycol) methyl ether | Polymer Source | P16082-EGOCH3NH2 | |
| Phosphate buffered saline tablet | Takara | T9181 | |
| Tween-20 | Calbiochem | 9480 | |
| Tris-HCl (pH 8.0) | Invitrogen | AM9855G | |
| KCl | Invitrogen | AM9640G | |
| NP-40 | VWR | E109-50ML | |
| Glycerol | Invitrogen | 15514-011 | |
| Dithiothreitol | Biosesang | D1037 | |
| Protease inhibitor | Merck | 535140-1MLCN | |
| Bromo phenol blue | Sigma-Aldrich | B5525-5G | |
| Tris-HCl (pH 6.8) | Biosolution | BT033 | |
| Sodium dodecyl sulfate | Biosolution | BS003 | |
| 2-Mercaptoethanol | Gibco | 21985-023 | |
| PKR Antibody | Cell Signaling Technology | 12297S | |
| GAPDH Antibody | Santa Cruz Biotechnology | sc-32233 | |
| Normal Rabbit IgG | Cell Signaling Technology | 2729S | |
| HeLa | Korea Cell Line Bank | 10002 | |
| Sonicator | DAIHAN Scientific | WUC-D10H | |
| Ultrasonicator | BMBio | BR2006A | |
| Centrifuge I | Eppendorf | 5424 R | |
| Centrifuge II | LABOGENE | 1736R | |
| Rotator | FINEPCR | ROTATOR/AG | |
| Vacuum oven | DAIHAN Scientific | ThermoStable OV-30 | |
| Gel permeation chromatography (THF) | Agilent Technologies | 1260 Infinity II | |
| X-ray photoelectron spectrometer | Thermo VG Scientific | Sigma Probe | |
| Dynamic light scattering | Malvern Instruments | ZEN 3690 |
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