Introduction to Phage Display
A phage (an abbreviated term for a bacteriophage) is a virus that infects bacteria. Consisting of a nucleic acid molecule surrounded by a protein structure, it hijacks the cellular machinery of a bacterium, forcing it to produce viral components. These components are assembled to form new phages and the bacterium is then destroyed by lysis as the phage particles are released. Since phages typically have a relatively simple genome and multiply rapidly to produce high titres, they have been exploited for a powerful technique known as phage display.
Phage display was first described in 1985 when foreign DNA fragments were inserted into a gene encoding a coat protein of filamentous phage, a type of bacteriophage which infects E. coli. Without impacting on the phage’s ability to infect the bacterial cells, the resulting fusion protein was displayed at the phage surface. Using antibodies directed against the foreign component of this protein, it was possible to enrich protein-expressing phages from the supernatant of bacterial cultures. Because this approach directly linked the genotype of the phage to the phenotype, phage display offered researchers a simple method of cloning a gene in situations where an antibody against the gene product was available.
Since its discovery, phage display has become a widely used method to create libraries containing vast numbers of different protein variants. These can be screened within a very short timescale to provide detailed information regarding the interaction of phage-expressed proteins with specific binding partners. To achieve this, the phage display library is exposed to a target molecule which has been immobilized on a solid support. Following incubation, unbound phages are washed away, and bound phages eluted. Phages with specificity for the target can be used to infect new host cells for amplification. Alternatively, multiple rounds of incubation, washing and elution can be performed to select those phages which bind with the greatest efficiency; this is a process known as panning.
The phage display cycle.
Although phage display sounds simple, in practice it is highly complex. Consideration must be given to the selection of an appropriate phage display system, including the choice of strain, the phage coat protein within which the foreign DNA will be inserted, and whether a helper phage is required to supply essential structural proteins. It is also necessary to consider the type of support on which the target will be immobilised (e.g. microtiter plate wells, PVDF membrane, column matrix, magnetic beads) and to carefully optimise each phase of the selection cycle. In addition, a well-designed panning procedure is essential to identify phages most suitable to the ensuing downstream application.
By partnering with an experienced provider of phage display services, researchers can benefit from high-quality phage display library construction and custom phage display library screening services to meet a range of exacting requirements. This can save significant amounts of time and resource, while providing unique insight to accelerate research. At Pivotal Scientific, we’re ideally placed to put you in touch with trusted partners specialised in applying advanced phage display technologies for a wide range of projects.