| Autor: |
T.D. Panosian, Ilsoo Kim, Ameer N. Thompson, Tina M. Iverson, Crina M. Nimigean, Toby W. Allen |
| Jazyk: |
angličtina |
| Předmět: |
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| Zdroj: |
Biophysical Journal. (3):660a |
| ISSN: |
0006-3495 |
| DOI: |
10.1016/j.bpj.2008.12.3487 |
| Popis: |
KcsA channel pores are blocked by intracellular Na+ and Li+ ions. We are investigating Na+/Li+ binding locations using electrophysiology, X-ray crystallography, and molecular dynamics simulations. We found that intracellular Li+ blocks KcsA channels with low, voltage-dependent affinity and competes with K+ for the blocking site. Its movement to the blocking site is not coupled with movement of permeant ions in the field. In contrast, Na+ blocks with less affinity and larger voltage dependence. We proposed that both small cations block in the hydrated vestibule with Na+ binding deeper in the pore at a site requiring partial dehydration while Li+ resides lower, remaining fully hydrated. Molecular dynamics calculations indicated low affinity binding for Na+/Li+ in the cavity but also predicted a high affinity binding-site in the S4 site, not “in-cage” where K+ ions bind but “in-plane” coordinated by Thr75 carbonyl oxygens. In search for all potential Li+ binding-sites we crystallized KcsA in the presence of Li+. Consistent with the MD results, we found three potential binding sites, one of which is in the S4 site of the selectivity filter in the plane of the Thr75 carbonyls. This suggests that Li+ and Na+ may be favored to bind in the S4 site but that they need to overcome a large energy barrier to get there. MD simulations unveil such barriers through free energy calculations involving multiple ion mechanisms for the smaller ions. We are now investigating experimentally the existence of a high-affinity binding-site inside the selectivity filter for both Na+ and Li+. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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