[RASMB] Query concerning membrane protein sedimentation equilibrium experiment

[Karen Fleming]

There's a statistical treatment for the issue of more than one  
protein molecule per micelle, and this can be described by a Poisson  
distribution. See
The GxxxG-containing transmembrane domain of the CCK4 oncogene does  
not encode preferential self-interactions.
Kobus FJ, Fleming KG.

Biochemistry. 2005 Feb 8;44(5):1464-70.

The other issue is that membrane proteins cannot necessarily be  
thought of as binding a "micelle's worth" of detergent molecules.  
(See Marc Le Maire's work). This is especially true when their  
molecular weights get larger. Therefore, monomers and multimers may  
bind different numbers of detergent molecules and therefore the  
buoyant molecular weight of the protein-detergent complex may be  
different for monomers+detergent as compared to multimers+detergent.  
We always got around this by density matching the detergent, but  
sometimes that's not possible for the system.

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On Nov 3, 2009, at 8:07 AM, Arthur Rowe wrote:

> Hi John (and everyone)
>
> That sounds good to me. Of course you could have more than one  
> protein monomer contained in each micelle - but that should be  
> immediately obvious from the M value.
>
> Kind regards
>
> Arthur
>
> --
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> Arthur J Rowe
> Professor of Biomolecular Technology
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>
> From: John_Doran at vrtx.com
> Date: Mon, 2 Nov 2009 16:46:47 -0500
> To: rasmb at rasmb.bbri.org
> Subject: [RASMB] Query concerning membrane protein sedimentation  
> equilibrium experiment
>
>
>
> We have measured the amount of detergent bound to our membrane  
> protein and hence were able to calculate a Vbar for the protein  
> detergent complex. Is it sufficient to just substitute this value  
> for Vbar along with the density value of the detergent buffer  
> solution into the ideal species equation of heteroanalysis to get  
> an accurate molecular weight value of the protein-detergent  
> complex, or is it more involved than that? Any thoughts concerning  
> this would be appreciated. Thank you.
>
> John Doran
> Vertex Pharmaceuticals
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