Structure of the KvAP voltage-dependent K+ channel and its on the lipid membrane

Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2005; 102(43):15441-6. DOI: 10.1073/pnas.0507651102
Source: PubMed


Voltage-dependent ion channels gate open in response to changes in cell membrane voltage. This form of gating permits the propagation of action potentials. We present two structures of the voltage-dependent K(+) channel KvAP, in complex with monoclonal Fv fragments (3.9 A) and without antibody fragments (8 A). We also studied KvAP with disulfide cross-bridges in lipid membranes. Analyzing these data in the context of the crystal structure of Kv1.2 and EPR data on KvAP we reach the following conclusions: (i) KvAP is similar in structure to Kv1.2 with a very modest difference in the orientation of its voltage sensor; (ii) mAb fragments are not the source of non-native conformations of KvAP in crystal structures; (iii) because KvAP contains separate loosely adherent domains, a lipid membrane is required to maintain their correct relative orientations, and (iv) the model of KvAP is consistent with the proposal of voltage sensing through the movement of an arginine-containing helix-turn-helix element at the protein-lipid interface.

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    • "revealed that the top of the S3 transmembrane domain is farthest away from the center of the pore, followed by S1 and that the extracellular loop between the S3 and S4 transmembrane domains are the closet to the channel pore. The subsequently solved crystal structures of different Kv channels (Lee et al. 2005; Long et al. 2005) indicated that although these distances were systematically shorter than the atomic distances, the arrangement of transmembrane helices was correct. Reexamination of the data revealed that using 50 % block yield similar distances as seen in the crystal structure (Morin and Kobertz 2008b), demonstrating that these molecular tape measures provide a straightforward approach to determine the radial arrangement of helices around the pore of K + channels. "
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    • "Flexible or unfolded segments, in some cases, make it difficult to estimate the structural proximity; we were not able to evaluate the data for the loops. On the other hand, the cross-linking approach for the membrane-spanning helices has been used successfully to examine the helix proximity (Careaga and Falke, 1992; Wu and Kaback, 1997; Wu et al., 1998; Dmitriev et al., 1999; Lainé et al., 2003; Lee et al., 2005). Cross-linking ratios were plotted against the mutation sites, and we found a periodicity in the variation (Fig. 3 C). "
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