Antibody Binding Affinities

to Protein A and Protein G

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