Channel selectivity, electrostatic

Noskov, S.Y. Berneche, S. Roux, B., Control of ion selectivity in potassium channels by electrostatic and dynamic properties of carbonyl ligands, Nature 2001,431, 830-834. 

K+ channels selectively transport K+ across membranes, hyperpolarize cells, set membrane potentials and control the duration of action potentials, among a myriad of other functions. They use diverse forms of gating, but they all have very similar ion permeabilities. All K+ channels show a selectivity sequence of K+ Rb+ > Cs+, whereas the transport of the smallest alkali metal ions Na+ and Li+ is very slow—typically the permeability for K+ is at least 104 that of Na+. The determination of the X-ray structure of the K+-ion channel has allowed us to understand how it selectively filters completely dehydrated K+ ions, but not the smaller Na+ ions. Not only does this molecular filter select the ions to be transported, but also the electrostatic repulsion between K+ ions, which pass through this molecular filter in Indian file, provides the force to drive the K+ ions rapidly through the channel at a rate of 107-108 per second. (Reviewed in Doyle et al., 1998 MacKinnon, 2004.)... 

Barrett, J. 2002. Atomic Structure and Periodicity. Cambridge The Royal Society of Chemistry. Bichet, D., M. Grabe, Y.N. Jan, and L.Y. Jan. 2006. Electrostatic interactions in the channel cavity as an important determinant of potassinm channel selectivity. P. Natl. Acad. Sci. USA 103 14355-1460. 

Boda D, Valisko M, Henderson D, Eisenberg B, Gillespie D, Nonner W (2009) Ionic selectivity in L-type calcium channels by electrostatics and hard-core repulsion. J Gen Physiol 133(5) 497-509... 

Functionalization of the matrix allows incorporation of a variety of catalytic activities into the material. Recently, procedures were developed to add functional groups that are electrostatically or hydrophobically attractive to the ammonium surfactant head groups and are able to compete with silicate anions during self-assembly. This has led to a class of mesoporous materials that are functionalized only on the inside of the pores. Highly selective polymerization and cooperative catalytic systems have been developed from these materials.3 Furthermore, by incorporating caps onto the pores, chemical reagents can be stored in the channels,... 

Electrostatic interactions between fibrils and a surface can be exploited to create micron-sized patterns of fibrils. Mesquida and colleagues (2005) used this approach to selectively deposit fibrils onto negatively charged stripes of mica that were exposed between alternating stripes of deposited cationic poly-L-lysine, as shown in Figure 9. The striped pattern was formed by directing poly-L-lysine through the channels of a polydi-methysiloxane (PDMS) stamp that was placed in contact with the mica surface. 

Immediately below the selectivity filter, which comprises the narrowest part of the ionophore, the channel opens up into a cavity (10 A in diameter) that holds a pool of water to stabilize and shield an ion from what would otherwise be the most hydrophobic part of the membrane. Additional stabilization is provided by the C-termini end of the four pore helices which have substantial negative electrostatic potential due to the helix dipole and point right at the pool.9 The hydrophobic lining of the pool is also probably conducive to the high flux of ions by providing a low-resistance pathway. 

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