In order to deal with the hay fever, we first considered to find the pollen causing the allergy and use engineered bacteria to prevent the pollen from the nose or phagocytose the pollen, but then we find this is nearly impossible because different flowers have different pollens, which means we need to design different types of bacteria to deal with them. Thus, then we change to focus on the histamine. Histamine is one of the most important cause for the allergy. If the concentration of histamine in the blood is high, the allergy will happen. Thus, we want to use engineered bacteria to sense the histamine, kill the histamine and alert the patients.
By consulting, we know that someone developed a riboswitch, which can sense the histamine and give some response.  There is a histamine aptamer on the 5’UTR which has high affinity with histamine. When the aptamer doesn’t bind with histamine, the ribosome can’t bind on the ribosome binding site, so the translation won’t happen, which means the riboswitch is off. However, if the aptamer binds with the histamine, the structure of the rna will be changed, and the ribosome can bind on the ribosome binding site. Thus, the translation can happen, and the riboswitch is on. We plan to apply that riboswitch in our program. It can successfully be the sensor of the histamine. If the histamine concentration is high, the riboswitch will become on and make some reaction start. However, the riboswitch doesn’t work very well in the E. coli, so we plan to use the artificial cell to contain the riboswitch.
Figure 1：The model of artificial cell which contains the riboswitch.
Figure 2: The opening of the riboswitch to make the translation on when the histamine bind with the aptamer.
Then we find someone used engineered bacteria to produce rDAO to kill the histamine.  DAO is a kind of enzyme that can kill the histamine, and rDAO is the DAO in the rat. So we plan to engineer the E. coli to let it express the gene of rDAO. Thus, it can produce rDAO to kill the histamine.
We also find β-ionone can be produced byβ- carotene reacting with CCD4.  CCD4 is an enzyme that can cleave β- carotene to yield β-ionone. β-ionone is a chemical that can release some fragrance. It can be found in some flowers, and also is used in making some perfume. So we plan to useβ-ionone to alert the patients.We will engineer the E. coli to express the gene of CCD4 and useβ- carotene as substrate to produceβ- ionone.
Figure 3: Cleaving β-carotene to yield β-ionone by using CCD4.
Thus, we get our final design. We plan to design an unguent which will be put into users’ nasal passages. The composition of the unguent is some artificial cells. The artificial cell will containβ- ionone and rDAO which are produced by the engineered E. coli. We also put the riboswitch into the artificial cell, so when the histamine concentration is high in the nose, the aptamer will bind with the histamine, and start the translation. The translation will produce the lipase which is an enzyme can break the artificial cell. Thus, the rDAO andβ-ionone will be released. rDAO can decrease the histamine concentration, so the allergy will be stopped before you feel the symptoms. β-ionone will let the users smell the scent, so they will be alerted and know that the histamine concentration is high.
Figure 4: The releasing of rDAO and β-ionone when the concentration of histamine is high.
Also, we find that we can design a test paper to test whether the food you buy is fresh because the high concentration of histamine means the food is not fresh. It will also use the riboswitch mentioned above, but it won’t be used to translate lipase rather than lac z. The expression of lac z will change the test paper color. Thus, if the histamine concentration is high, the color of test paper will get changed, so people will know the food isn’t fresh.
Figure 5: The operating principle of test paper.
. Programmable Artificial Cells Using Histamine-Responsive Synthetic Riboswitch (by Mohammed Dwidar, Yusuke Seike, Shungo Kobori, Charles Whitaker, Tomoaki Matsuura, and Yohei Yokobayashi)
. Expression of rat diamine oxidase in Escherichia coli(by Elena Rosini , Serena Nossa , Mattia Valentino, Paola D’Arrigo, Stéphane Marinesco, Loredano Pollegioni)
. Overexpression and characterization of CCD4 from Osmanthus fragrans andβ-ionone biosynthesis fromβ-carotene in vitro(by Xuesong Zhang Jianjun Pei Linguo Zhao Feng Tang Xianying Fang Jingcong Xie)