Electrostatic basis of valence selectivity in cationic channels.
We examine how a variety of cationic channels discriminate between ions of differing charge. We construct models of the KcsA potassium channel, voltage gated sodium channel and L-type calcium channel, and show that they all conduct monovalent cations, but that only the calcium channel conducts divalent cations. In the KcsA and sodium channels divalent ions block the channel and prevent any further conduction. We demonstrate that in each case, this discrimination and some of the more complex conductance properties of the channels is a consequence of the electrostatic interaction of the ions with the charges in the channel protein. The KcsA and sodium channels bind divalent ions strongly enough that they cannot be displaced by other ions and thereby block the channel. On the other hand, the calcium channel binds them less strongly such that they can be destabilized by the repulsion of another incoming divalent ion, but not by the lesser repulsion from monovalent ions.
Corry
Ben
B
Chemistry, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley, WA, 6009, Australia. ben@theochem.uwa.edu.au
Vora
Taira
T
Chung
Shin-Ho
SH
D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D016012:Poisson Distribution; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry / Q000378:metabolism*; D055672:Static Electricity; D013302:Streptomyces / Q000378:metabolism
D001426:Bacterial Proteins; D020746:Calcium Channels, L-Type; D015221:Potassium Channels; D015222:Sodium Channels; C107790:prokaryotic potassium channel; D012964:Sodium; D011188:Potassium; D002118:Calcium