| Popis: |
While single channel recordings readily discern whether a K+ pore is in a conducting or non-conducting state, the same does not apply to crystal structures of K+ channels. There is at present no cogent means for demarcation of physiological state, or for pinpointing non-native structure arising when a channel is removed from the natural environment of a bilayer. The nature of molecular reconfiguration during gating remains indistinct (other than significant variability in width of the intracellular aperture). Defining a consistent set of molecular indicators of physiological state would lay a solid foundation for interpretation of K+ channel structure, and enhance its usefulness to the biophysics community.The architecture of the potassium selective pore is conserved in all known K+ channels indicating that the core of the gating process may be universal, even though the means by which opening is instigated differs between families. We have targeted a single type of potassium channel for structure determination in conducting, intermediate, and non-conducting states. Our rationale is that excluding effects due to familial differences will pin down structural features reflecting the physiological gating transition. This initial study uses prokaryotic Kir channels, which are a good structural model for eukaryotic inward rectifiers. Our data suggest that discrete structural fingerprints characterise open and closed states.An earlier study in collaboration with D.A. Doyle yielded the structure of a prokaryotic inward rectifier (KirBac1.1). Complete obstruction of the pore by phenylalanine side chains denoted an unambiguously non-conductive state, providing a structural reference point. A close homologue, KirBac3.1, has now yielded several further structures that collectively reveal a pattern of molecular rearrangement. A consistent sketch is emerging. Additionally, a reduction to 2-fold symmetry in some structures, particularly pronounced in the intracellular regions, indicates that Kir channel opening occurs stepwise. |
