Team:NWU-China/Kcsa Modify

KcsA Modify

The selective filter is the central structure of the ion channel,which is also the narrowest part of the channel. Its amino acid sequence is TVGYG from77-79[1], which is the same in all potassium channels. The carbonyl oxygen atoms on the amino acid sequence point inward toward the ion channel and form four ion-binding sites on the potential energy.

After simulation,reading dissertation[2][3] and with the help of AEMD(Automation Enzyme Muatation Design) 链接From NPU , we decide to mutate Gly77 to D-Ala77.

The free enegy landscape of simulation progress about Na+ get through the selective filter shows that there is a energy barry when Na+ get through the site of Gly77.So the best way for us is to mutate the Gly77.

We don't make a great change on the filter or the narrow may fatally expand that loses the ability of specific selective. The side chain of Gly is -H(or it doesn't have side chain) ,the most similar group is -CH3 ,So we try mutating to Ala77 first. But the simulation told us that the methyl of Ala77 in each subunit would point to the centre of the narrow, which totally blocks the channel.

And alternative try is mutating to D-Ala,which is the same as Ala but chirality.The simulation is very successful and shows that the addition 4 methyls affect the structure of selective filter to have a 0.16A average displacement on the filter atoms.A profound change it brought is that the channel will keep open.

The other novel characteristic is that the new channel can pass Na+.the new landscape shows that the barry of Na+ get though residue 77 is weaken.But the channel is still 'more favourite' to K+,so the channel pass K+ under the high concentration of K+ and allow the Na+ get though when the K+ concentration is low.

[1] Benoît Roux Ion channels and ion selectivity Essays in Biochemistry Essays Biochem. 2017 May 09; 61(2): 201–209
[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] Francis I. Valiyaveetil,* Manuel Leonetti, Tom W. Muir,† Roderick MacKinnonIon Selectivity in a SemisyntheticK+ Channel Locked in theConductive Conformation Science 314 (5801), 1004-1007.