The present invention provides an Ecoli host cell expressing a recombinant antibody characterized in that the Ecoli host cell has been genetically modified in order to change at least one physical property of one or more Ecoli proteins which in the wild type copurify with said recombinant antibody.
1. An E. coli host cell expressing a recombinant antibody wherein the E. coli host cell has been genetically modified in order to change the isoelectric point of the E. coli Phosphate binding protein (PhoS/PstS) wherein the isoelectric point has been altered by: (a) the addition of a poly-aspartic acid tag to the C-terminus of the Phosphate binding protein and/or (b) changing one or more of the amino acid residues located on the surface of the E. coli Phosphate binding protein (PhoS/PstS) by (i) substituting one or more lysine and/or arginine residues with aspartic acid or a glutamic acid or (ii) substituting one or more aspartic acid and/or glutamic acid residues with lysine or arginine.
2. The host cell of claim 1 where the isoelectric point of the Phosphate binding protein (PhoS/PstS) has been reduced by substituting one or more lysines at residues 110, 265, 266 or 318 with glutamine or aspartic acid.
3. The host cell of claim 2 where the isoelectric point of the Phosphate binding protein (PhoS/PstS) has been reduced further by the addition of a poly-aspartic acid tag to the C-terminus.
4. The host cell of claim 1 where the isoelectric point of the Phosphate binding protein (PhoS/PstS) has been reduced by substituting the lysines at residues 265 and 266 with glutamine and by the addition of a poly-aspartic acid tag to the C-terminus.
5. The host cell of claim 1 where the isoelectric point of the Phosphate binding protein (PhoS/PstS) has been reduced by substituting the lysines at residues 110, 265 and 266 with glutamine and by the addition of a poly-aspartic acid tag to the C-terminus.
6. The host cell of claim 1 where the recombinant antibody is a Fab or a Fab′ fragment.
7. A method of manufacturing a recombinant antibody which comprises fermenting a host cell according to claim 1 .