Human proteins processed in vivo need muti-step posttranslational modification (Folding, glycosylation and et al), such as TGFbeta superfamily processing. Furin is a protein in human cleaves these sections and activates TGF superfamily proteins. Non-human cells do not have the processing machinery (E Coli, et al). Human cells do. They are able to produce correct disulfide bonds, glycosylation and right structure.

Cell type	Human Cell	E. Coli Cell
Cell Picture
ER	With	Without
Golgi	With	Without
Mitochondria	With	Without
Lysosome	With	With
Ribosome	With	Without