Affinity Chromatography - Department of Molecular and Cellular ...
Affinity Chromatography - Department of Molecular and Cellular ...
Affinity Chromatography - Department of Molecular and Cellular ...
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Antibody classes<br />
Characteristic<br />
Heavy chain<br />
Light chain<br />
IgG<br />
IgM<br />
g<br />
m<br />
a<br />
e<br />
d<br />
k or l k or l k or l k or l k or<br />
IgA<br />
IgE<br />
IgD<br />
l<br />
Y structure<br />
Fig. 10. Antibody classes.<br />
IgG, IgG fragments <strong>and</strong> subclasses<br />
The basis for purification <strong>of</strong> IgG, IgG fragments <strong>and</strong> subclasses is the high affinity <strong>of</strong> protein A<br />
<strong>and</strong> protein G for the Fc region <strong>of</strong> polyclonal <strong>and</strong> monoclonal IgG-type antibodies, see<br />
Figure 9.<br />
Protein A <strong>and</strong> protein G are bacterial proteins (from Staphylococcus aureus <strong>and</strong> Streptococcus,<br />
respectively) which, when coupled to Sepharose, create extremely useful, easy to use media<br />
for many routine applications. Examples include the purification <strong>of</strong> monoclonal IgG-type<br />
antibodies, purification <strong>of</strong> polyclonal IgG subclasses, <strong>and</strong> the adsorption <strong>and</strong> purification<br />
<strong>of</strong> immune complexes involving IgG. IgG subclasses can be isolated from ascites fluid, cell<br />
culture supernatants <strong>and</strong> serum.<br />
Table 2 shows a comparison <strong>of</strong> the relative binding strengths <strong>of</strong> protein A <strong>and</strong> protein G to<br />
different immunoglobulins compiled from various publications.<br />
A useful reference on this subject is also: Structure <strong>of</strong> the IgG-binding regions <strong>of</strong> streptococcal<br />
Protein G, EMBO J., 5, 1567–1575 (1986).<br />
Binding strengths are tested with free protein A or protein G <strong>and</strong> can be used as a guide to<br />
predict the binding behaviour to a protein A or protein G purification medium. However,<br />
when coupled to an affinity matrix, the interaction may be altered. For example, rat IgG 1<br />
does not bind to protein A, but does bind to Protein A Sepharose.<br />
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