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unexpected 40kDa band -E.coli protein expression - (Nov/20/2008 )

Hi all, I would like your opinion on one thing. I express a biotin tagged 21 kDa protein (Ras) in E. coli and purify it using agarose-neutravidin beads. after purification I have a good yield of my protein but there is an extra (and weaker) band around 40 kDa. neutravidin is 60 kda so I don't think it is that. any ideas what it could be? thanks in advance.


Probably a dimer or some complex?


There is a nice review in Nature Methods Vol.5 No.2 p135. Could be DnaJ (41kDa) according to the paper, which co purifies by IMAC.

-lost higo-


U can never be surely, if the seen band is a complex of ur protein or just a contaminated protein in ur system from

the host cell. U have to do W.B to the protein and check for extra or specific band.

good luck