[ccp4bb] Off-topic Thrombin cleavage

[Yuri Pompeu]

Dear community,
I am trying to cleave a hexaHis tag from my protein prior to crystallization.
As I was setting up my digestion, my protein started to precipitate as soon as 
I added the recommended thrombin buffer.
My question is, if anyone has encountered this, how well does it cleave without 
thrombin buffer?
or even, without the CaCl2? Any other buffer/conditions known to work?
thanks in advance