expressed protein is 5-6kda bigger than

[lmcmurry_tet at opal.tufts.edu]

for what it is worth, ptoeins in SDS gels can run several kD differently due to
a single amino acid change! I have seen this my self, also in the literature. 
Also, not related to the 6H problem., but hydrophobic proteins usually run too
fast by up to 15%in SDS gels; the putative explanation is that they bind MORE sds than
normal, since the sds is binding by its hydrobphbic chain to the protein.In article <4vido3$l1c at gwdu19.gwdg.de>, wdl at gen.mpib-tuebingen.mpg.de (Wulf
Dirk Leuschner) writes:
> imazhq at leonis.nus.sg (Zheng Huanquan) wrote:
> 
>>Does anyone have such experience that expressed protein is 5-6kda bigger 
>>that native one? my protein is 33kda and has additional 13aa + 6x His, 
>>thus the expressed protein should 35-36kda, but I only got 40-42kda 
>>expressed. Any explain? 
> 
>>thank you!
> 
>>Hugo Zheng
> 
> Hi Hugo,
> 
> it depends in what kind of organism you have the protein expressed. If
> it is, e.g., in mammalian cells, glycosylation might be the problem. 
> Sometimes proteins have 'abnormal' mobilities in SDS-PAGE (although
> their  molecular weight is correct) due to some conformation (even
> with SDS!) which influences the migration properties of the protein.
> 
> WDL
>