Ecoli contaminant Histag purification

[Satish Nair]

Luc CAMOIN wrote:
> 
> Dear Netters,
> 
>         We tried to purify our His-tagged recombinant protein expressed in
> Ecoli using Nickel affinity purification columns. Two proteins were
> retained and eluted at 100 mM imidazole. These two proteins were sequenced.
>         One was a FKBP-TYPE PEPTIDYL-PROLYL CIS-TRANS ISOMERASE SLYD from
> Ecoli. This protein was known to bind Ni with high affinity.
>         The second one was a chaperonin protein GROEL from Ecoli. This
> protein contains one His and one Cys.
>         Has anybody identified already this last proteins in immobilized
> metal affinity chromatography?
>         Does anyone have any explanation about this binding?
> 
>         Thanks in advance
> 
> Luc CAMOIN

The GroEL is probably not binding to the resin as much as it is 
probably binding to your protein (as a chaperonin involved in protein
folding, it would make sense that it would bind to your protein).  
You may want to look up (Trends in Genetics, Vol. 12 p. 209) as it
mentions one possible way of ridding the GroEl contaminant.