Team:Edinburgh/Efficiency

— Jawaharlal Nehru

Is display of cellulases via phage or INP any good, even in theory?

Consider this: for a bacteria to produce phage or INP requires energy. This energy could have been spent producing extra copies of the cellulases. In order for the phage and cell display projects to make sense, the benefits of synergy must outweigh the cost of producing all these extra proteins.

This question can probably be investigated using simple maths and back-of-envelope calculations...

Cell display

For the cell display system, the carrier protein INP (which is fused to a cellulase) is about two thirds the size of any of the cellulases. Each cellulase thus has a final size of about 66% above normal.

So if the synergystic system works at over 166% efficiency compared to the standard system where enzymes are free-floating in the media, cell display via INP makes sense.

Phage display

The situation with phage is more complex. To produce one phage requires over 200,000 amino acids, whereas each cellulase is roughly 500 amino acids in size. The efficiency of the system will depend on how many cellulases are displayed on each phage.

There are approximately 2,700 pVIII coat proteins on the phage for us to display enzymes on. However, displaying enzymes on too many copies destabilises the phage causing it to disintegrate. The theoretical maximum is supposed to be about 20%. If we could display enzymes on 20% of the coat proteins, we would have 540 enzymes on the phage, using about 500,000 amino acids in total.

These 540 enzymes would thus only have taken 66% more amino acids than normal to make, and the situation is similar to that for cell display.

However, that is an extreme example. In all probability the number of enzymes displayed on the phage will be much less. So, how many enzymes must be displayed on the phage before the system makes sense?

A best-case scenario would be if the synergistic effects of having the enzymes in close proximity made them 50 times more efficient (this number is suggested and critiqued by Fontes and Gilbert, 2010).

References

• Fontes CMGA, Gilbert HJ (2010) Cellulosomes: highly efficient nanomachines designed to deconstruct plant cell wall complex carbohydrates. Annual Review of Biochemistry 79: 655-81 (doi: 10.1146/annurev-biochem-091208-085603).