Format

Send to

Choose Destination
Biochemistry. 2004 May 4;43(17):4978-82.

Ion binding affinity in the cavity of the KcsA potassium channel.

Author information

1
Howard Hughes Medical Institute and Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, 1230 York Avenue, New York, New York 10021, USA.

Abstract

The hydrophobic cell membrane interior presents a large energy barrier for ions to permeate. Potassium channels reduce this barrier by creating a water-filled cavity at the middle of their ion conduction pore to allow ion hydration and by directing the C-terminal "end charge" of four alpha-helices toward the water-filled cavity. Here we have studied the interaction of monovalent cations with the cavity of the KcsA K(+) channel using X-ray crystallography. In these studies, Tl(+) was used as an analogue for K(+) and the total ion-stabilization energy for Tl(+) in the cavity was estimated by measuring its binding affinity. Binding affinity for the Na(+) ion was also measured, revealing a weak selectivity ( approximately 7-fold) favoring Tl(+) over Na(+). The structures of the cavity containing Na(+), K(+), Tl(+), Rb(+), and Cs(+) are compared. These results are consistent with a fairly large (more negative than -100 mV) electrostatic potential inside the cavity, and they also imply the presence of a weak nonelectrostatic component to a cation's interaction with the cavity.

PMID:
15109256
DOI:
10.1021/bi049876z
[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for American Chemical Society
Loading ...
Support Center