KcsA is a homotetrameric 68-kDa membrane-associated potassium channel which selectively gates the flux of potassium ions across the membrane. The channel is known to undergo a pH-dependent open-to-closed transition. Here we describe an NMR study of the monomeric subunit of the channel (KcsAM), solubilized in SDS micelles. Chemical shift, solvent exchange, backbone 15N relaxation and residual dipolar coupling (RDC) data show the TM1 helix to remain intact, but the TM2 helix contains a distinct kink, which is subject to concentration-independent but pH-dependent conformational exchange on a microsecond time scale. The kink region, centered at G99, was previously implicated in the gating of the tetrameric KcsA channel. An RDC-based model of KcsAM at acidic pH orients TM1 and the two helical segments of the kinked TM2 in a configuration reminiscent of the open conformation of the channel. Thus, the transition between states appears to be an inherent capability of the monomer, with the tetrameric assembly exerting a modulatory effect upon the transition which gives the channel its physiological gating profile.
|Number of pages||11|
|Journal||Biochimica et Biophysica Acta - Biomembranes|
|State||Published - Dec 2007|
Bibliographical noteFunding Information:
We thank Dr. Alex Grishaev for his assistance with the RDC fitting algorithms and Annie Aniana for the technical assistance in sample preparation. J.H.C. acknowledges the support of a long-term EMBO fellowship. This work was supported by the Intramural Research Program of the NIDDK, NIH, and by the Intramural AIDS-Targeted Antiviral Program of the Office of the Director, NIH.
- Membrane proteins
- Potassium channel
- Solvent exchange