Production of human serum transferrin in Escherichia coli.

Transferrin (Tf) crystals diffract to only medium resolution. The mediocre quality of the crystals may be due to two factors: (1) the genetic variations naturally present in the primary sequence of Tf, and (2) the glycosylation of the protein. To control genetic variations and glycosylation of samples of Tf, it would be desirable to express the Tf gene from a recombinant clone. Additionally, expression of Tf from a clone would allow for manipulation of the structure of Tf. The cDNA encoding Tf has been cloned into the pL-based expression vector, pRE1, and the T7-based expression vectors, pRSETA and pET11A. The Tf expression plasmids, pTF-SSn and pTF-ESn, based on the T7 expression vectors, efficiently produce a 76-kDa protein that is approximately the same size as deglycosylated Tf, cross reacts with anti-Tf antibodies, and matches the deduced N-terminal amino acid sequence. Expression of Tf in Escherichia coli will allow the production of genetically pure, unglycosylated protein.