Recombinant Antibody Fragment Production in the Antarctic Marine Bacterium Pseudoalteromonas haloplanktis TAC125

Abstract

Within the biopharmaceutical industry, the antibody market is one of the fastest-growing segments, due to wide applications of recombinant antibodies and antibody fragments in research, diagnostics and therapy. Large-scale production of this protein class requires the use of a platform characterised by low costs, accessible for genetic modifications and easily scaled up. Although their production in prokaryotic hosts can significantly lower production costs, recombinant antibody production in conventional bacterial hosts, such as Escherichia coli, may result in formation of inclusion bodies. As protein solubility (and consequently its correct folding) may be enhanced by lowering of the expression temperature, a novel process for recombinant antibody fragment production at low temperatures was set up using Pseudoalteromonas haloplanktis TAC125 as recombinant expression host. To test the versatility of the new process developed in the Antarctic Gram-negative bacterium, three model proteins, corresponding to the most common formats of antibody fragments, were produced: Fab, scFv and VH. Several critical aspects were considered in the construction of an ad hoc genetic expression system for each model protein, including the selection of molecular signals for periplasmic protein translocation and the choice of an optimal gene-expression strategy. For instance, an artificial operon was designed and constructed for Fab fragment production in fully heterodimeric form. Furthermore, a novel defined minimal medium was made up to maximise bacterial growth parameters and recombinant production yields. All antibody fragments were produced in soluble and biologically competent form. The observed ability of the Antarctic bacterium to produce recombinant antibody fragments was justified by the observation that P. haloplanktis TAC125 genome contains an unusually high number of genes encoding peptidyl-prolyl cis-trans isomerases, making this bacterium the host of choice for the recombinant production of this protein class.