Function E: Cell Lysis

This is a detailed description of an individual function of our circuit. To access other functions and get an overview of the whole circuit, visit the Circuit page.

Introduction

Bacteria can be engineered to deliver various cargos to specific locations in different ways. CATE is designed to recognize the tumor (see Tumor Sensor), accumulate the Anti-Cancer Toxin and deliver it on-demand via the Heat Sensor. To actually release a substance from the bacteria to the environment, different strategies can be utilized, such as taking advantage of secretion systems that many bacteria possess or engineering the bacteria to undergo lysis in response to an external signal. [1]

The delivery method

The release of the Anti-Cancer Toxin from our system is designed to happen once both Checkpoint 1 and Checkpoint 2 have been passed. This means that the toxin has successfully been accumulated inside of the bacteria and is ready to be delivered to the tumor. Considering that simultaneous release of the full dose of the toxin is desirable, we decided that synchronized bacterial cell lysis should be our method of choice.

The lytic agent

Protein E, our weapon of choice, is a protein produced by phage Phi X 147, which (in nature) lyses the host cell after production of phage particles. [2] We decided to use it because it has already been successfully implemented to achieve cell lysis in engineered bacteria [3] and it was kindly provided to us by Dr. Irene Wuthrich from our department, along with advice on how to work with it.

The exact mechanism of action of protein E has long been controversial and different models were proposed to explain its lytic function. It has been suggested that protein E activates a component of the E. coli autolytic system, that it inhibits cell wall synthesis in a manner similar to penicillin or that it oligomerizes to form a transmembrane tunnel, all leading to release of cytoplasmic content and ultimately cell death. [4][5][6]

However, it is now generally accepted that the most probable cellular target of protein E is an enzyme called Translocase I, encoded by the mraY gene. Translocase I seems to play an important role for cell wall biosynthesis and its inhibition leads to cell lysis. The "transmembrane tunnel" model has largely been discarded and the tunnels are now attributed to faulty cell wall synthesis, making it a consequence rather than the cause. [4]

Protein E and CATE

In our design, protein E is the mediator of cell lysis. Once the Anti-Cancer Toxin has accumulated and the MRI Contrast Agent has signalled passage through Checkpoint 1, the physician can apply focused ultrasound to activate the Heat Sensor. Activation of the Heat Sensor leads to production of protein E, which quickly results in cell lysis and toxin release.

References