Isolation of trans-acting genes that enhance soluble expression of scFv antibodies in the E. coli cytoplasm by lambda phage display

Genetically modified bacteriophages

Applications of genetically modified bacteriophages.

PhiXing-it, displaying foreign peptides on bacteriophage ΦX174

Although bacteriophage φX174 is easy to propagate and genetically tractable, it is use as a peptide display platform has not been explored. One region within the φX174 major spike protein G tolerated 13 of 16 assayed insertions, ranging from 10 to 75 amino acids. The recombinant proteins were functional and incorporated into infectious virions. In the folded protein, the peptides would be icosahedrally displayed within loops that extend from the protein׳s β-barrel core. The well-honed genetics of φX174 allowed permissive insertions to be quickly identified by the cellular phenotypes associated with cloned gene expression. The cloned genes were easily transferred from plasmids to phage genomes via recombination rescue. Direct ELISA validated several recombinant virions for epitope display. Some insertions conferred a temperature-sensitive (ts) protein folding defect, which was suppressed by global suppressors in protein G, located too far away from the insertion to directly alter peptide display.

Bacteriophages as scaffolds for bipartite display: designing swiss army knives on a nanoscale

Bacteriophages have been exploited as cloning vectors and display vehicles for decades owing to their genetic and structural simplicity. In bipartite display setting, phage takes on the role of a handle to which two modules are attached, each endowing it with specific functionality, much like the Swiss army knife. This concept offers unprecedented potential for phage applications in nanobiotechnology. Here, we compare common phage display platforms and discuss approaches to simultaneously append two or more different (poly)peptides or synthetic compounds to phage coat using genetic fusions, chemical or enzymatic conjugations, and in vitro noncovalent decoration techniques. We also review current reports on design of phage frameworks to link multiple effectors, and their use in diverse scientific disciplines. Bipartite phage display had left its mark in development of biosensors, vaccines, and targeted delivery vehicles. Furthermore, multifunctionalized phages have been utilized to template assembly of inorganic materials and protein complexes, showing promise as scaffolds in material sciences and structural biology, respectively.

Selection for intrabody solubility in mammalian cells using GFP fusions

Single-chain antibody fragments (scFv) expressed in the cytoplasm of mammalian cells, also called intrabodies, have many applications in functional proteomics. These applications are, however, limited by the aggregation-prone behaviour of many intrabodies. We show here that two scFv with highly homologous sequences and comparable soluble expression levels in Escherichia coli cytoplasm have different behaviours in mammalian cells. When over-expressed, one of the scFv aggregates in the cytoplasm whereas the second one is soluble and active. When expressed at low levels, using a retroviral vector, as a fusion with the green fluorescent protein (GFP) the former does not form aggregates and is degraded, resulting in weakly fluorescent cells, whereas the latter is expressed as a soluble protein, resulting in strongly fluorescent cells. These data suggest that the GFP signal can be used to evaluate the soluble expression of intrabodies in mammalian cells. When applied to a subset of an E.coli-optimised intrabody library, we showed that the population of GFP+ cells contains indeed soluble mammalian intrabodies. Altogether, our data demonstrate that the requirements for soluble intrabody expression are different in E.coli and mammalian cells, and that intrabody libraries can be directly optimised in human cells using a simple GFP-based assay.