Team:Aalto-Helsinki/Micelle

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Micelle

Based on the previous studies about this pathway [1, 2], we knew the propane yields weren’t very high. We thought about trying to enhance the system by looking for homologs for the enzymes, but thought this would be too time-consuming but also not very innovative. We then ran into a research article by Huber et al [3]. The group had designed a synthetic amphiphilic protein that spontaneously formed membrane-like structures inside the cell. These proteins we’re designed quite like membrane lipids: there is a hydrophilic and a hydrophobic end. According to the energy minimum principle, the proteins’ hydrophilic ends will face the liquid phase of the cell and the hydrophobic ends will pack together. This way the proteins will be able to form either a double layer (similar to the double lipid layer) or a micelle.

To both enhance the knowledge of these amphiphilic proteins and to gain a better yield of propane, we thought of fusing enzymes to these proteins. This would bring the enzymes close together and possibly enhance their productivity. Because our system is so big, we needed to make some compromises though - we didn’t think it was possible to attach all 10 of our pathway’s enzymes into these amphiphilic proteins, but decided to do it to two of the last enzymes: CAR & ADO. We chose these enzymes for two reasons, the first one being more significant. The product of CAR (and the substrate of ADO) is butyraldehyde, which is toxic to the cell. Therefore, if too much butyraldehyde is built up in the cell, we will lose our cell line. Also, because of the toxicity, cells have many endogenous enzymes that consume butyraldehyde, thus reducing the amount of available butyraldehyde to be converted into propane by ADO. Our second reason has to do with this. Our models suggest that ADO is a bottleneck in our system. Therefore we would like to try to keep its substrate concentration high in the close proximity of ADO, so that it can function as efficiently as possible.

In the situation where CAR and ADO are fused with the amphiphilic proteins, we expect the amphiphilic proteins to form micelles rather than membranes, as the enzymes will most probably repulse each other. This is why we are calling the system amphiphilic micelles, but in reality it doesn’t matter to us whether the formations are micelles or membranes because the enzymes will nevertheless be closer together in both formations.

We wanted to test our hypotheses with something we could easily detect. We found the Violacein pathway [4], which could by the use of three enzymes produce a detectable green color. We believe, that if the violacein green color production could be enhanced by fusing these enzymes with the amphiphilic proteins, we could have an idea of whether the propane production could as well be enhanced in a similar way. There are obviously differences between these systems, but it would give us a rough estimate of whether these types of constructs would be possible to build in the first place.