Structure and Energetics of Allosteric Regulation of HCN2 Ion Channels by Cyclic Nucleotides.
Bottom Line: Binding of cyclic nucleotides increases the rate and extent of channel activation and shifts it to less hyperpolarized voltages.We probed the allosteric mechanism of different cyclic nucleotides on the CNBD and on channel gating.We explain these results with a model where different allosteric mechanisms in the CNBD all converge to have the same effect on the C-linker and render all three cyclic nucleotides similarly potent activators of the channel.
Affiliation: From the Departments of Chemistry, Physiology and Biophysics, and.Show MeSH
Mentions: The magnitudes of the chemical shift perturbations for the assigned resonances are plotted in Fig. 4. Residues with chemical shifts that disappeared or could not be tracked upon addition of cyclic nucleotide are shown in gray. A comparison of the chemical shift perturbations induced by binding cGMP or cCMP relative to chemical shift perturbations induced by binding cAMP is shown in supplemental Fig. S1. If the CNBD were to sample only two conformations, the chemical shift perturbations of cAMP, cGMP, and cCMP would be expected to be collinear. However, a comparison of chemical shift perturbations indicates that they are not collinear (Figs. 3, B and C, and supplemental Fig. S1). In contrast to these findings, a previous study with the HCN4 isoform found that the cCMP and cAMP chemical shift perturbations fell largely along a line (32). Differences in the HCN isoform used in these experiments may be the cause of this discrepancy. Our results indicate that the HCN2 CNBD is not limited to sampling two conformations corresponding to cyclic nucleotide bound and unbound, but rather operates in a more complex conformational landscape, adopting different conformations depending on which cyclic nucleotide species is bound. The nature of the structural differences between these conformations is unknown at this point.
Affiliation: From the Departments of Chemistry, Physiology and Biophysics, and.