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Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

Published: July 20th, 2016



1School of Chemistry, The Australian Centre for Nanomedicine and the ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, The University of New South Wales

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.

We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Bioconjugation involves covalently linking one biomolecule with another or with a synthetic molecule such as a dye, drug or a polymer. Protein bioconjugation methods are now extensively used in many chemistry, biology and nanotechnology research groups with applications ranging from fluorescent dye labelling1,2, making of protein (antibody)-prodrugs3 (antibody drug conjugates — ADCs) synthesis of protein dimers4,5, through to self-assembling protein-polymer hybrids6,7 used in nanomedicine8 and systems chemistry9.

Specificity of the chemistry used for bioconjugation, whi....

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Note: The following protocol is designed for the synthesis of a protein-dye bioconjugate as shown in Figure 1. It is a general protocol for the reaction of a maleimide with free surface cysteine containing proteins, with notes inserted where applicable to assist with membrane protein bioconjugates, protein-polymer bioconjugates, and synthetic protein dimer (protein-protein) bioconjugates. In this particular case, the protein iso-1 cytochrome c has one surface cysteine residue available to react which allows a highly.......

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The synthesis of bioconjugates is confirmed by three primary methods: Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS), polyacrylamide gel electrophoresis, and Ultraviolet-Visible (UV-Vis) spectroscopy, as shown in Figures 2, 3 and 4. A mass increase corresponding to the mass of the appended small molecule, and the lack of an unreacted protein demonstrates the successful covalent linkage of Ru(II) (tpy)2

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Purification of the starting materials before a bioconjugation is of utmost importance. Proteins obtained from commercial recombinant sources often contain other isoforms of the protein of interest, which can have different surface chemistry and reactivity. For example, in the described bioconjugation, the commercially available cyt c contains a mixture of both iso-1 and iso-2 cyt c12,14,17. Iso-2 and iso-1 forms of cytochrome c are largely homologous, with the main difference being .......

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We thank the Australian Research Council (ARC) for ARC Future Fellowship (FT120100101) and ARC Centre of Excellence CE140100036) grants to P.T. and the Mark Wainwright Analytical Centre at UNSW for access to mass spectrometry and NMR facilities.


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Name Company Catalog Number Comments
sodium dihydrogen phosphate Sigma-Aldrich 71496
sodium hydroxide Sigma-Aldrich 71691
sodium chloride Sigma-Aldrich 73575
cytochrome c, from saccaromyces cerevisiae Sigma-Aldrich C2436
dithiothreitol Sigma-Aldrich 43819
TSKgel SP-5PW Sigma-Aldrich Tosoh SP-5PW, 07161 3.3 mL strong cation exchange column
Amicon Ultra-15  Merck-Millipore UFC900308 3.5 kDa spin filter
Slide-A-Lyzer mini dialysis units Thermo Scientific 66333 3.5 kDa dialysis cassetes
Ru(II) bisterpyridine maleimide Lab made see ref (14)
acetonitrile Sigma-Aldrich A3396
ethylenediaminetetraacetic acid Sigma-Aldrich 03609
tris(2-carboxyethyl)phosphine hydrochloride  Sigma-Aldrich 93284
imidazole Sigma-Aldrich 56749
nickel acetate Sigma-Aldrich 244066
AcroSep IMAC Hypercell column Pall via VWR: 569-1008 1 mL IMAC column
0.2 micron cellulose membrane filter Whatman Z697958 47 mm filter for buffers
0.2 micron PVDF membrane filter Merck-Millipore SLGV013SL syringe filters for proteins
hydrochloric acid Sigma-Aldrich 84426 extremely corrosive! Use caution
caffeic acid Sigma-Aldrich 60018 MALDI matrix
trifluoroacetic acid Sigma-Aldrich 91707 extremely corrosive! Use caution
SimplyBlue SafeStain Thermo Scientific LC6060 Coomassie blue solution
NuPAGE Novex 12% Bis-Tris Gel Thermo Scientific NP0342BOX precast protein gels
SeeBlue Plus2 Pre-stained Protein Standard Thermo Scientific LC5925 premade protein ladder
NuPAGE LDS Sample Buffer (4X) Thermo Scientific NP0008 premade gel sample buffer
NuPAGE Sample Reducing Agent (10X) Thermo Scientific NP0004 premade gel reducing agent
NuPAGE MES SDS Running Buffer (20X) Thermo Scientific NP0002 premade gel running buffer
Voyager DE STR MALDI reflectron TOF MS Applied Biosystems
Acta FPLC GE Fast Protein Liquid Chromatography
Cary 50 Bio Spectrophotometer Varian-Agilent UV-Vis
Milli-Q ultrapure water dispenser Merck-Millipore ultrapure water
Low volume UV-Vis Cuvette Hellma 105-201-15-40 100 microliter cuvette

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