Enhancing expression of recombinant proteins in mammalian cells using the herpesvirus VP16 transactivator

Separation used for purification of recombinant proteins

The purification of molecules from recombinant cells may be strongly influenced by the molecular biology of gene isolation and expression. At the beginning of the process there may be a demand for information on the minute amounts of proteins and thus for ever increasingly sensitive techniques. Purification of recombinant proteins can differ from conventional purifications in several ways, depending on the solubility of the protein, occurrence in inclusion bodies, creation of fusion proteins with tags that enable simpler purification. Sometimes a (re)naturation step is required to get a bioactive protein. On the other hand, the techniques used in separation are essentially the same as for purification from the natural source and environment.

Phage presentation and affinity selection of a deletion mutant of human interleukin-3

A deletion derivative of the cytokine human interleukin-3 (hIL-3(15-125), comprising amino acids 15-125 of the native protein) was produced as a fusion to the filamentous phage surface protein pIII. The cytokine was detected in association with phage particles by protein immunoblotting. Compared to an equivalent quantity of soluble-cytokine, phage-presented hIL-3(15-125) exhibited reduced biological activity in a hIL-3-dependent cell proliferation assay. The reduction in activity was attributable to presence of phage particles in the assay, rather than directly owing to physical incorporation of the cytokine into the phage particle. Owing to the position of the amber codon in the phagemid vector, the phagemid-produced free hIL-3(15-125) species (designated hIL-3(15-125) epsilon) had 20 amino acids appended to its C-terminus; hIL-3(15-125) epsilon did not exhibit reduced bioactivity. hIL-3(15-125)-presenting phage were affinity-selected with either a hIL-3-reactive polyclonal antibody or with cells expressing the heterodimeric hIL-3 receptor. These data are consistent with the use of phage-display technology for the affinity selection of hIL-3 variants with modified biological properties.