Difference between revisions of "Part:BBa K1954001"

Revision as of 14:16, 20 October 2016

This is UCL iGEM 2016's nomination for Best New Composite Part as well as its new BioBrick submission for a Silver Medal (Experimentally validate that at least one new BioBrick Part or Device of your own design and construction works as expected).

For UCL iGEM 2016's entry for the Gold Medal criterion, 'Improve the function OR characterization of a previously existing BioBrick Part or Device', please go to: BBa_K239009.

Lycopene cassette under the control of NarK, an oxidative stress inducible promoter

Lycopene expression under control of NarK promoter to enable cells to grow better under conditions of stress.

Usage and Biology

Lycopene is an antioxidant naturally occuring in tomatoes, giving them their rich red colour. This antioxidant is also known to be lacking in the elderly population, meaning there are higher levels of unregulated oxidative stress. This BioBrick is induced by oxidative stress and produces lycopene as means to 'mop up' the oxidative stress in the environment, in the form of a probiotic.
After choosing our topic of healthy ageing we spoke to various researchers in the area. We especially valued the opportunity to speak to Aubrey De Grey, an author of books such as 'advocate for an indefinite human lifespan' and 'ending ageing'. He is the co-founder of SENS research and is renowned in the field for his research. We were particularly looking forward to discussing the idea of a antioxidant probiotic with him following his interest in the free radical theory of ageing and his positive view that "Ageing is emphatically not an inescapable destiny".
In conversation with Aubrey de grey, it was suggested to us that our lycopene probiotic would need to be controlled. This is because reactive oxide species are useful in important signalling processes which act to protect the cell. Taking on board this advice, we considered a method to control lycopene expression.
To achieve this we decided to look through the registry at existing promoter which would select lycopene expression only in 'high stress' conditions which mimic the imbalance of stress within the cell. Hence, we decided to combine lycopene with a stress sensitive promoter which would only release lycopene when cells are stressed. This promoter was NarK. We are very grateful to Aubrey for his insight and enthusiasm for our project, and also thankful that he took time to speak with our team and influence our project in a positive way.

To watch our conversation see our wiki page: http://2016.igem.org/Team:UCL/HP/Silver/Experts.

Early in our discussion of what we could target in ageing, we spoke to various academics, including Dr. Max Yun, a Senior Research Associate in the UCL’s Division of Biosciences who recommended a paper to us - ‘The Hallmarks of Ageing’. This highlighted not only is ageing a complex, multi-faceted problem, but also that it wouldn’t be possible to target all hallmarks, instead, we chose to focus on reactive oxygen species (ROS) which underpin some of the hallmarks (1) of ageing.

For instance, endogenous damage caused by ROS leads to DNA lesions including telomerase shortening(1). These lesions essentially lead to genomic instability (1). Ageing in this instance is caused by imbalance between DNA damage and DNA repair, for instance insufficient repair mechanism or excessive DNA damage promotes ageing (1).

Oxidative stress can also cause proteins to unfold and aggregate, again leading to ageing (1). We found greater strength in this argument when we were shown data from research undertaken at Imperial University showing oxidative stress to have a detrimental impact upon protein stability. The consequence of this is in turn reflected in protein activity and hence ageing. A description of these results is included below.

We have been researching the link between protein aggregation and oxidative stress. By using Dynamic Light Scattering (DLS), we were able to see that the size of a protein (monoclonal antibody) changed in the presence of oxidative stress. Under oxidative stress the protein becomes unstable and either undergoes a conformational change forming an unstable intermediate with a radius of a bit more than 1nm (as seen in image 2), or it aggregates (seen as the 2nd peak (at ~100-1000nm of the 2nd picture). 5mM of Hydrogen Peroxide was used to induce oxidative stress.

We also did some experimentation using Self-Interaction Chromatography (SIC) (data not shown). Without oxidative stress we get a nice peak and the area under the peak can be used to calculate the 2nd Osmotic Virial Coefficient (B2). B2 is a dimensionless no. that indicates protein stability. A positive B2 means that the proteins particles repel each other and will tend not to aggregate, but a negative B2 means that the protein is unstable, as its particles have a net attractive interaction and will aggregate. Without oxidative stress, the protein is stable with a B2 of 0.66.

<img src=""> Protein without oxidative stress <img src=""> Protein with oxidative stress

However, when the same protein is exposed to oxidative stress we have a negative B2 value of -21 meaning that the protein is very unstable. This is because oxidative stress causes particle-particle interaction to become very high and very attractive. This means that the particles begin to take more and more time interacting with each other and the column attracts the mAb and heavily disrupts the flow of it.

In conclusion, oxidative stress has a very significant impact on protein stability. As you age and there is more oxidative stress in the body, the proteins in our cells which are essential to healthy functioning become unstable/aggregate, thereby leading to a loss of activity. This loss of activity of the essential proteins leads to the deterioration of health, so targeting oxidative stress to promote healthy ageing can be an effective strategy.

Clearly the impact of oxidative stress upon protein structure is significant and since structure and function are inexplicably, linked the functionality of the proteins are likely to be hindered too. Thus, we are looking towards preventative methods that will lessen the amount of oxidative stress that proteins are exposed to. Sequence and Features