Secretion of a bacterial protein by mammalian cells.

The MalE protein is a periplasmic maltooligosaccharide binding protein from Escherichia coli. This protein is widely used as a model for protein export in bacteria and as a vector for the export and one-step affinity purification of foreign polypeptides. Expression of MalE was studied in various animal cell lines. The protein was exported into the culture medium, following the classical pathway of eukaryotic protein secretion. This was shown by a combination of approaches including the use of inhibitors of the Golgi complex and immunocytological methods. The signal sequence of MalE is required for secretion and a specific signal can be added to MalE that targets it to the endoplasmic reticulum. This work opens the way to the study of the secretion of a bacterial protein and to its use as a vector for protein secretion and purification from mammalian cells.