Team:NWU-China/Design
Design
We meet the problem
The lopsided ratio of ions(too much Na+ and less K+) of saline soil could affect the growing of the crop[1] such as wheat and rice.
The high concentration of Na+ in sea water limits our range of drinking water.
How to solve the problem
To solve those problems ,we need to distinguish the potassium ions and the sodium ions.But because of the similarity between K+ and Na+ (radius of ion and chemical charaters), it is very difficult to distinguish them in solution. And alternatively we need to exclude or absorb sodium ions in an efficient way.We decided to use ion channel to meet both requirements simultaneously.
Why we choose ion channel
Ion channel is a protein that locals in the membrane of cell.The selectivity carried by the structure can identify different ions ,open for the particular ion and resist the others from get through the channel.And the transfering rate of channel is so high that reachs 10^8 ions per second [2], near to the diffusion rate .Alternatively the transfering process is hardly wrong.We use KcsA(https://2018.igem.org/Team:NWU-China/Kcsa_Modify) potassium ion channel ,which from the soil bacteria Streptomyces lividans that has been studied extensively in ion channel research[3].
The modify on the channel
The wild potassium channel is not enough,we need to get a channel with a more powerful function. After trying and researching ,we find a way to get a novel characteristic.
The fantistic KcsA* channel protein can absorb K+ under the high concentration of K+ and allow the Na+ get though when the K+ concentration is low.
Extend the codon
The mutated channel protein includes a D-Ala, so we decided to generate a path to introduce a non-natrual amino acid into the protein expressing system[4].
We design a new path with tRNAD-Ala D-AlaRS Alr KcsA* .
part
Here are the parts we design: 
Experiment
We will connect those part into psb1c3 and then introduce into the bacteria to express the protein.
After then ,we will test the ability of absorbing ions of bacteria.
We will extract the KcsA to test the function by Patch Clamp and a new method.
We will also extract the D-AlaRS to test the ability of specifically select D-Ala.
[1] Kehui Xie, Yong Deng, Shaocun Zhang, Wenhao Zhang, Jianrong Liu, Yulong Xie, Xuze Zhang, and He Huang Prokaryotic Community Distribution along an Ecological Gradient of Salinity in Surface and Subsurface Saline Soils Sci Rep. 2017; 7: 13332.
[2] David Medovoy, Eduardo Perozo, and Benoît Roux Multi-ion free energy landscapes underscore the microscopic mechanism of ion selectivity in the KcsA channel Biochim Biophys Acta. 2016 July 1858(7 Pt B): 1722–1732
[3] Cuello LG, Cortes DM, Perozo E.The gating cycle of a K+ channel at atomic resolution.Elife. 2017 Novbr
[4] Nediljko Budisa Prolegomena to Future Experimental Efforts on Genetic Code Engineering by Expanding Its Amino Acid Repertoire Angew. Chem. Int. Ed. 2004, 43, 6426 – 6463