Antibody Binding Affinities to Protein A and Protein G

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Overview
Protein A and protein G
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Overview

Depending on their host species and isotype, antibodies have different binding affinities to protein A and protein G. These properties are especially critical when deciding whether to use protein A or protein G coupled agarose, sepharose or magnetic beads in your immunoprecipitation experiments. While the binding affinity differences to protein A or protein G for a human IgG1 antibody may be minimal, for other antibodies the differences are severe; for example rat Ig2a does not bind to protein A but has a strong binding affinity to protein G.

In addition to immunoprecipitation experiments, the choice between protein A and protein G is also critical when selecting the best antibody purification method or kit.

Antibody Host Species, Isotype and Subtype	Protein A	Protein G
Bovine IgG	**	****
Chicken IgY	x	*
Goat IgG	*/x	**
Guinea Pig IgG	********	**
Hamster IgG	*	**

Human IgG1	********	****
Human IgG2	********	********
Human IgG3	x	****
Human IgG4	****	****
Human IgA	**	x
Human IgD	**	x
Human IgE	**	x
Human IgM	**	x

Mouse IgG1	*	**
Mouse IgG2a	********	********
Mouse IgG2b	***	***
Mouse IgG3	**	***
Mouse IgM	*/x	*

Pig IgG	*******	*******
Rabbit IgG	****	***

Rat IgG1	x	*
Rat IgG2a	x	********
Rat IgG2b	x	**
Rat IgG2c	*	**
Rat IgM	*/x	x

Sheep IgG	*/x	**

Binding affinity ratings:

**** = Strong binding affinity
*** = Moderate binding affinity
** = Weak binding affinity
* = Very weak binding affinity
x = No binding affinity

Table and legend were adapted from here

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