Post translational modification??

Frank Fuerst ffrank at
Tue Jan 30 10:38:01 EST 2001

Mano <mdep at> wrote:

>Hi all,
>    I am studying the expression of two highly homologous proteins
>(approximately 50 kDa).  In fact their published sequence differs by
>only ONE amino acid.  Using a monoclonal antibody that detects BOTH
>proteins, I can resolve the two proteins by SDS page as if there is a
>5kDa difference, when in fact there is only one amino acid difference.
>At this time, there is no evidence for phosphorylation differences or
>glycosylation differences.
>    Does anyone have any ideas as to why I can see such a big difference
>by SDS PAGE even thought the proteins are only 1 amino acid difference
>in length?

Are you sure that they are really denatured by SDS? We are working
with a protein that is completely resistant to SDS, but migrates well
in SDS-PAGE because of it's own charge. If a surface amino acid is
replaced and the replacement causes a charge alteration, we can well
resolve the difference.

The same might occur even if the protein is not completely resistant,
as long as the assumption that the charge is proportional to the amino
acid number is wrong.

Bye, Frank

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