Affinity Chromatography - Department of Molecular and Cellular ...

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Elution There is no generally applicable elution scheme for all affinity media. Reference to manufacturer's instructions, the scientific literature and a few simple rules should result in an effective elution method that elutes the target protein in a concentrated form. Elution methods may be either selective or non-selective, as shown in Figure 5. Method 1 The simplest case. A change of buffer composition elutes the bound substance without harming either it or the ligand. Method 2 Extremes of pH or high concentrations of chaotropic agents are required for elution, but these may cause permanent or temporary damage. Methods 3 and 4 Specific elution by addition of a substance that competes for binding. These methods can enhance the specificity of media that use group-specific ligands. Fig. 5. Elution methods. When substances are very tightly bound to the affinity medium, it may be useful to stop the flow for some time after applying eluent (10 min. to 2 h is commonly used) before continuing elution. This gives more time for dissociation to take place and thus helps to improve recoveries of bound substances. Selective elution methods are applied in combination with group-specific ligands whereas non-selective elution methods are used in combination with highly specific ligands. Forces that maintain the complex include electrostatic interactions, hydrophobic effects and hydrogen bonding. Agents that weaken these interactions may be expected to function as efficient eluting agents. The optimal flow rate to achieve efficient elution may vary according to the specific interaction and should be determined when necessary. Further details on the kinetics involved in binding and elution of target molecules from affinity media are covered in Appendix 7. A compromise may have to be made between the harshness of the eluent required for elution and the risk of denaturing the eluted material or damaging the ligand on the affinity medium. Ready to use affinity media from Amersham Pharmacia Biotech are supplied with recommendations for the most suitable elution buffer to reverse the interaction between the ligand and target protein of the specific interaction. Each of these recommendations will be based on one of the following elution methods: 18
pH elution A change in pH alters the degree of ionization of charged groups on the ligand and/or the bound protein. This change may affect the binding sites directly, reducing their affinity, or cause indirect changes in affinity by alterations in conformation. A step decrease in pH is the most common way to elute bound substances. The chemical stability of the matrix, ligand and target protein determines the limit of pH that may be used. If low pH must be used, collect fractions into neutralization buffer such as 1 M Tris-HCl, pH 9 (60–200 µl per ml eluted fraction) to return the fraction to a neutral pH. The column should also be re-equilibrated to neutral pH immediately. Ionic strength elution The exact mechanism for elution by changes in ionic strength will depend upon the specific interaction between the ligand and target protein. This is a mild elution using a buffer with increased ionic strength (usually NaCl), applied as a linear gradient or in steps. Enzymes usually elute at a concentration of 1 M NaCl or less. Competitive elution Selective eluents are often used to separate substances on a group specific medium or when the binding affinity of the ligand/target protein interaction is relatively high. The eluting agent competes either for binding to the target protein or for binding to the ligand. Substances may be eluted either by a concentration gradient of a single eluent or by pulse elution, see page 22. When working with competitive elution the concentration of competing compound should be similar to the concentration of the coupled ligand. However, if the free competing compound binds more weakly than the ligand to the target molecule, use a concentration ten-fold higher than that of the ligand. Reduced polarity of eluent Conditions are used to lower the polarity of the eluent promote elution without inactivating the eluted substances. Dioxane (up to 10%) or ethylene glycol (up to 50%) are typical of this type of eluent. Chaotropic eluents If other elution methods fail, deforming buffers, which alter the structure of proteins, can be used, e.g. chaotropic agents such as guanidine hydrochloride or urea. Chaotropes should be avoided whenever possible since they are likely to denature the eluted protein. 19
Page 1 and 2: Affinity Chromatography Principles
Page 3 and 4: Affinity Chromatography Principles
Page 5 and 6: Serine proteases and zymogens with
Page 7: Appendix 4 ........................
Page 10 and 11: This handbook describes the role of
Page 12 and 13: Affinity chromatography is also use
Page 14 and 15: BioProcess Media for large-scale pr
Page 17 and 18: Chapter 2 Affinity chromatography i
Page 19: Avoid using magnetic stirrers as th
Page 23 and 24: 0.6 0.4 0.2 0 A280 pH selected for
Page 25 and 26: Situation Cause Remedy Protein does
Page 27 and 28: Chapter 3 Purification of specific
Page 29 and 30: Table 2. Relative binding strengths
Page 31 and 32: Purification examples Figure 11 sho
Page 33 and 34: MAbTrap Kit Fig. 13. MAbTrap Kit, r
Page 35 and 36: Media characteristics Ligand Compos
Page 37 and 38: A 280 nm 2.0 1.5 1.0 0.5 Column: rP
Page 39 and 40: Desalt and/or transfer purified IgG
Page 41 and 42: Performing a separation Column: Rec
Page 43 and 44: M r 97 000 66 000 45 000 30 000 20
Page 45 and 46: in The Recombinant Protein Handbook
Page 47 and 48: Cleaning These procedures are appli
Page 49 and 50: Purification examples Figures 24 an
Page 51 and 52: Nickel solution: 0.1 M NiSO 4 Bindi
Page 53 and 54: Protein A fusion proteins IgG Sepha
Page 55 and 56: Purification or removal of serine p
Page 57 and 58: Sample: 2 ml clarified E. coli homo
Page 59 and 60: Serine proteases and zymogens with
Page 61 and 62: DNA binding proteins HiTrap Heparin
Page 63 and 64: Sample: Column: Binding buffer: Elu
Page 65 and 66: Media characteristics Ligand densit
Page 67 and 68: Sample: Pooled and frozen human pla
Page 69 and 70: The harsh conditions required to br
Page 71 and 72:
Purification or removal of albumin
Page 73 and 74:
IFN-act. A units 280 nm 250 0.12 20
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Purification options Binding capaci
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Sepharose NH (CH 2) n NH N N O N N
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If detergent or denaturing agents h
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Glycoproteins or polysaccharides Co
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For complex samples containing glyc
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For complex samples containing glyc
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Chemical stability Avoid exposure t
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Proteins and peptides with exposed
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Several methods can be used to dete
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Media characteristics Composition M
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Performing a separation Binding buf
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Do not store the suspension for lon
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Sepharose has been modified and dev
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Ligand coupling Several methods are
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Couple a ligand through the least c
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Table 9 summarizes recommended liga
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Coupling through the primary amine
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Ligand and column preparation 1. Di
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Options Product Spacer Coupling con
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100 80 Coupled substance, % 60 40 2
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Coupling small ligands through amin
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Ligand coupling 1. Add the ligand s
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Alternative coupling solutions: Dis
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Media characteristics Product Compo
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Ligands containing amino groups can
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Chapter 6 Affinity chromatography a
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Resolution is achieved by the selec
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For any capture step, select the te
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Appendix 1 Sample preparation Sampl
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Remove salts from proteins with mol
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1. Filter (0.45 µm) or centrifuge
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For laboratory scale operations, Ta
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Removal of lipoproteins Lipoprotein
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Appendix 2 Selection of purificatio
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4. Estimate the amount of slurry (r
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Appendix 5 Conversion data: protein
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Middle unit residue (-H 2 0) Charge
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Expected results when changing cond
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Expected results with competitive e
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Appendix 8 Analytical assays during
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Appendix 9 Storage of biological sa
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Ordering information Product Quanti
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STREAMLINE, Sepharose, HiTrap, ÄKT
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