M13 phages

M13 is a filamentous phage that infects E. coli that carry the F-episome. Active infection with M13 does not kill the host cell. The M13 phage particle consists of a single-stranded DNA (ssDNA) genome encased in approximately 2700 copies of a major coat protein protein VIII.^[1]

Life cycle

M13 phage life cycle in Escherichia coli.

The M13 life cycle begins with passage of the phage genome into a host cell in a process induced by protein III (pIII). First, the single-strand DNA (ssDNA) is converted in double-strand DNA (dsDNA) by pII and pX, which allow the production of phage's protein.

After a while, as the concentrations of phage proteins increase and the ssDNA is back converted as dsDNA. The protein V (pV) binds to the ssDNA genomes for packaging into progeny phages. It recognise the single stranded M13 origin of replication. The pV-sequestered ssDNA is recognized by the membrane spanning phage assembly complex. ^[1]

Protein III

Description of the domains composing M13's protein III.

The molecular interactions that mediate the entry of Escherichia coli derived filamentous phages into their hosts have been studied in considerable detail. The 424-amino-acid protein III is thought to consist of a leader sequence and three domains, separated by glycine-rich regions, that serve distinct roles in phage entry and release. The first two pIII domains, D1 and D2, are required for M13 adsorption and entry, while the third domain D3 is required for the assembly and release of M13 particles from host.^[2]

Design

Phages-like particules

Bacteriophages are capable of expressing their genomes, and generating new copies of themselves. We choose to limit the phage ability to reproduce itself in order to contain it. As it is possible to produce recombinant viruses that express foreign proteins, it is possible to restrain their capacity to reproduce themself. ^[3]

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology. ^[3]

Engineering M13

In order to engineered multiple phages to infect various pathogenes we first decided to remove D1 and D2. As we wanted to insert those two domains in the p3 of the M13 genome. Thus we use M13KO7 from New England BioLab. M13KO7 is an M13 derivative which carries the mutation Met40Ile in gII , with the origin of replication from P15A and the kanamycin resistance gene from Tn903 both inserted within the M13 origin of replication.

In M13KO7 we wanted to insert two restriction site (AvrII and BspI) which are compatible with XbaI and AgeI. Thus, we create two types of biobrick, one with the signal sequence of M13, and the other one with D1 and D2 of another p3 from another filamentous phages.

In our design we wanted to keep the signal sequence and D3 of M13, because their are crucial for the formation of the phage. We just want to insert D1 and D2 from another phages (we’ll call it X).

Another way to engineered M13, is to remove entierely the protein III from the phage genome and to reconstruct it in another plasmid. Thus, we create another part : p3_D3, which is the domain involved in the assembly and release of M13 particles.

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Phagemid

As M13KO7 genome is not capable to be used for the phage assemblage, we will use a phagemid which will carry a toxin to assemble our ingeneered M13 phage.

We thought about using the Super Nova toxin (BBa_K1491017), made by the iGEM team Carnegie Mellon in 2014. This toxin has multiple benefits, because of the production of ROS occuring only in a yellow - orange light, we can produce phages-like particules carring this toxin without killing E.coli. However, when this toxin will be produced in X. fastidiosa with the light coming from the sun, the bacterium will be harmed, even if it is in the Xylem vessels. To optimise the production of this toxin in X. fastidiosa we tried to find a strong and constitutive promoter of this bacterium.

We thought about multiple ways to engineer our phagemid.

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References

1. ↑ ^{1.0 1.1} Smeal, S. W., Schmitt, M. A., Pereira, R. R., Prasad, A. & Fisk, J. D. Simulation of the M13 life cycle I: Assembly of a genetically-structured deterministic chemical kinetic simulation. Virology 500, 259–274 (2017).
2. ↑ Heilpern, A. J. & Waldor, M. K. pIIICTX, a predicted CTXphi minor coat protein, can expand the host range of coliphage fd to include Vibrio cholerae. J. Bacteriol. 185, 1037–1044 (2003).
3. ↑ ^{3.0 3.1} Roldão, A., Silva, A. C., Mellado, M. C. M., Alves, P. M. & Carrondo, M. J. T. Viruses and Virus-Like Particles in Biotechnology: Fundamentals and Applications. in Reference Module in Life Sciences (Elsevier, 2017).