a problem in protein purification

[yuling luo]

Hi there,

I am trying to purify a myc-tagged recombinant protein (pI=7.6, 100 kd) 
from the supernatant of baculovirus-infected insect cells. I first 
enriched the protein on a cation exchange column, which worked out fine. 
I then loaded the eluate into an anti-myc monoclonal affinity column and 
eluted the column with 0.1 M glycine pH 2.5. I found that most of the 
myc-tagged protein bound to the affinity column. But the eluted protein 
is in precipitated form. It become obvious when I netralize the elute to 
netral pH with Tris buffer. Then I would just see a big white precipitate 
forming. I also tried high pH elution buffer. The eluted protein is still 
precipitated. My questions are 1) could this be the problem of the 
affinity column itself? (if it is, I could try different ways to purify 
it) 2) Could this be the protein's problem? (ie, the protein will 
aggregate in the absence of other proteins, if this is the case, I am 
hopeless. 3) anyone out there has similar experience? 

Your advice is much appreciated.     yl