Protein A - FC binding...what really happens?

tmorris at tmorris at
Fri Aug 2 08:00:47 EST 2002

Thanks, Mike.

Forgive my ignorance. Does the V region refer to the hinge, and is this region variable, and is this why you say that only a proportion of IgGs will bind to it, or have I missed the point. 

Also, I had assumed the protein A molecule was fairly conserved. My protein A manufacturer gives Staph, aureus as the source organism. Is this enough information to conclude that different protein A batches, conjugates etc have identical binding characteristics, or are we talking about sub-species hybrid variability?

If you can cite anything relevent to to read it would help me immensely. I'm a neurobiologist! Thanks again for your insights. Basically I am up a creek with this project at the moment.


Mike Clark wrote:

> In article <20020801162158.12788.qmail at>,
> <URL:mailto:tmorris at> wrote:
> > Dear Colleagues:
> > 
> >  
> > 
> > I had always assumed that each IgG FC region could only bind one protein
> > A molecule. T he FC portion is referred to in literature in the singular
> > sense, even though it deriv es from portions of two heavy chains, and
> > this seems to be consistent with crystallogr aphic binding models as best
> > as I can understand them (Deisenhofer, 1981, Biochemistry ).
> > 
> [snip] 

> It is worse than you thought. Not only are there two potential Protein A
> binding sites in the Fc but thre are also two other potential binding
> sites, one in each Fab!

> Each molecule of Protein A, depending upon its source, might also have more
> than one binding site for Ig!

> Some V-region subgroubs are able to bind to Protein A which means that only
> a proportion of antibodies bind Protein A in the Fab.

> Mike                            <URL:>
> -- 
> M.R. Clark, PhD. Division of Immunology
> Cambridge University, Dept. Pathology
> Tennis Court Rd., Cambridge CB2 1QP
> Tel.+44 1223 333705  Fax.+44 1223 333875

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