protein mass weight different?

Peter Dudek peterd at
Thu Jun 21 20:22:12 EST 2001

How bout some more details. When you mean "much smaller", how much exactly?
For instance, hyperphosphorylated proteins (ones with say more than 5
phosphorylated residues) can be seen to migrate significantly higher than
their unphosphorylated form. You can see as much as a 10-15 kD difference in
some proteins.

Other possibilities (other than the already mentioned glycosylation):

(1) acylation
(2) methylation
(3) myristoylation
(4) sulfation
(5) prenylation

There are other post-translational modifications you can consider, but I
think they're less significant (at least in terms of their contribution to
overall molecular weight). Another possibility is that your E.coli expressed
protein is cleaved by endogenous proteases.

Whichever may be the case, perhaps your best bet is to send both samples to
a mass-spec facility (costly, but arguably the most precise). Anyways, I
hope this was helfpful.

Best of luck!


"Jun Zhang" <junzhang_cn at> wrote in message
news:20010620014440.28503.qmail at
> Hi, everyone
>           By immunoscreening methods,our lab has gotten a new gene.
> surprisingly, the protein mass weight that I expressed the gene in E.coli
> much smaller than that obtained by immunoprecipitation.
>     The first possibility we come into mind is that glycosylation.
>       But we can not find any glycosylation site in our predicted protein
> sequence.
>        Could you give me some suggestions?
> Many thanks!
>                                       Jun       zhang
> <>

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