Question about Protein A purification of IgG

Tom Barr mdp96tab at
Tue Oct 10 10:29:22 EST 2000

Protein A, isolated from S. aureus cell walls, has four antibody binding
sites (though only two can interact at one time). The protein interacts with
the second and third constant regions of the Fc portion (hydrophobic
interaction). As constant regions vary, so does protein A's affinity for
various IgG species (Good for human and guinea pig, moderate for mouse and
poor for rat).
Protein G is from streptococci C or G strains, and like protein A,
specifically binds Fc portions of Ab (naturally it also binds albumin too,
but this binding site is generally removed from commercial prot. G). Protein
G is reported to bind Fc portions with higher affinity, and is particularly
useful for isolating rat Ig.



aeon wrote:

> I am a Med.Sci. student who is really desiring the answers to these two
> questions for an upcoming report.
> 1. What is the molecular basis for the selective binding of IgG by protein
> A?
> 2. What is the difference between Protein A and Protein G in relation to
> their Ig class binding specificities?
> Thank you for your response.
> Aeon

Tom Barr (mdp96tab at
Division of Molecular and Genetic Medicine (F-Floor)
University of Sheffield Medical School
Beech Hill Road
S10 2RX

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