precipitation problems

[Lim Pohyam]

My bacterial recombinant proteins precipitates upon long storage at -20C. 
Upon thawing from freezer, I detected strands of precipitates. There is 
difficulty to re-suspend these strands. As a result, when I set up my 
microtiter plates, the activity is decreased. I sometimes encounter as much 
as 15-20% drop in protein concentration. This is creating havoc in my 
assays. I would like to receive feedback on how to remove this problem. what 
can I do? I keep losing my protein everytime I thawed them from the freezer!