Construction Of Artificial Ion Channel Based On Helical Polymer And α-hemolysin

There are many pores and channels which composed of different types of transporters in biological cells.They are distributed in the cell membrane and intracellularly,and control the exchange of ions and molecules in living organisms,affect cell functions and many life processes.Once the ion channel have gene mutation or deletion,its functional expression will be severely damaged,and causing human ion channel diseases,such as hereditary arrhythmia,various forms of diabetes,cystic fibrosis,myotonia,epilepsy,etc.Therefore,the research on the structure of ion channels,ion transport mechanism,and ion transport selection mechanism have attracted widespread attention in the academic community.Further,based on the study of the properties of biological channels,great efforts have been made to design and synthesize artificial ion channels to improve the understanding of the transport selection mechanism of natural channel proteins,and to develop their application potential in the fields of biosensors,energy conversion,and drug delivery.In the past few decades,a variety of artificial ion channels have been reported.Artificial nanochannels have analogous structures and functions to biological channels,which can be used as biological counterparts of natural channels,simulating the ion transport process of natural channel proteins,and explaining their selection mechanisms.However,based on the current research,there is still a large gap in the performance between artificial channels and natural channels.How to improve ion transmission efficiency,control the sensitivity of the system,and achieve specific ion selectivity are the outstanding problems currently facing.There,it’s of great significance and research value to further construct artificial channels with high selectivity and high throughput.Based on the above considerations,pyridine-oxadiazole containing oxygen atoms was chosen as the structural motif.Due to the electrostatic repulsion,the pyridineoxadiazole unit would undergo bending and folding,which provides basic conditions for the formation of a hollow helical structure.And through π-π interactions,the molecules stacked each other and formed a stable helical structure.Finally,a helical polymer with an inner cavity rich in oxygen atoms was obtained to mimic the active site of natural channel proteins.In addition,the nanopores of α-hemolysin were functionally modified to construct artificial ion channels with alkali metal ion selectivity.This work will further enrich the artificial ion channel model and deepen the understanding of ion selectivity and ion transport rate.1.Construction of artificial ion transmembrane channels based on helical polymers.The active site of the native potassium ion channel protein(Kcs A)consists of four conserved signature sequences,among which,TVGYG(threonine-valine-glycinetyrosine-glycine)acts as a selectivity filter(SF)to conduct K+.The narrowest part of the selectivity filter is only 12 (?).It is lined with hydrophobic amino acids,and carbonyl oxygen atoms are arranged inside.The carbonyl oxygen atoms can coordinate with K+,so that the potassium ion channel has stronger selectivity for K+ than Na+.Inspired by this,we used pyridine-oxadiazole as the basic unit to synthesize an aromatic helical polymer with rich oxygen atoms inside the cavity,and modified hydrophobic side chains.The oxygen atoms in the cavity of the aromatic helical polymer can serve as the binding site for potassium ions,and the external hydrophobic side chains help it to embed into the lipid bilayer to form transmembrane pores.According to computer theoretical simulation calculations,the cavity size of the aromatic helical polymer is3.4 (?),and the pitch is 3.42 (?),which is slightly larger than K+.Therefore,K+ and Na+ can be efficiently transported,and the results showed that its transport efficiency for K+ and Na+ was in the same order of magnitude as that of natural gramicidin.2.Construction of artificial ion channel based on α-hemolysin nanopore.As a natural pore-forming protein,α-hemolysin has the advantages of natural cavity and membrane insertion.Based on its stable structure,easy-to-modify cavity and good biocompatibility,many different functionalized α-hemolysins have been constructed by means of gene mutation and chemical modification,which have widely used in the field of single-molecule detection and biosensing.Based on theoretical simulation calculations,the 8-position lysine of α-hemolysin is mutated to glutamic acid,and the17-position asparagine is mutated to aspartic acid through gene mutation,and a negative potential cavity α-hemolysin nanopore was constructed.In addition,we synthesized a helical polymer with amino side chains based on pyridine-oxadiazole,which would be attracted by the negative potential of the nanopore and vertically enter the cavity of the nanopore,making the nanopore obtain ion selective transmission properties.The natural nanopore advantage of α-hemolysin promoted the accumulation of cations and accelerated the ion transport rate of artificial ion channels.In summary,this work constructed a new type of artificial ion channel model by modifying the nanopores of natural proteins,and provided more references for the construction of artificial ion channels in the future.