soluble protein expression in E. coli

[Saverio Brogna Genetics]

Dear someone,
I have expressed e protein in E. coli with differents systems (His-tag, 
Glutation-transferase fusion and wild-type) but I can not get it soluble.
DO YOU KNOW HOW TO EXPRESS PROTEINS IN A WAY THAT SOME IS SOLUBLE?

Thanks
-- 
Saverio Brogna
University of Cambridge, Departement of Genetics
Downing Street, Cambridge, CB2 3EH, England (UK)
tel +44-223-333970, fax +44-223-333992