membrane protein aggregation - (Mar/28/2010 )

I expressed a membrane protein in insect cell . The expression level is reasonable. At low concentration, the protein is quite stable and the fplc profile is good. But once at high concentration, more than half of the protein went to aggregate.

Is there anybody could give me some suggestion how to improve it ?

Thanks!

add something that may prevent aggregation (eg ethylene glycol, peg-8000 1-5%) and limit concentration.