Cyclic Purine and Pyrimidine Nucleotides Bind to the HCN2 Ion Channel and Variably Promote C-Terminal Domain Interactions and Opening

• Published in: Structure (London) 2016-10, Vol.24 (10), p.1629-1642
• Main Authors: Ng, Leo C.T., Putrenko, Igor, Baronas, Victoria, Van Petegem, Filip, Accili, Eric A.
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites; Crystallography, X-Ray; Cyclic CMP - metabolism; Cyclic IMP - metabolism; Dynamic Light Scattering; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels - chemistry; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels - metabolism; Mice; Models, Molecular; Potassium Channels - chemistry; Potassium Channels - metabolism; Protein Domains; Protein Structure, Secondary
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2016.06.024

Cyclic AMP is thought to facilitate the opening of the HCN2 channel by binding to a C-terminal domain and promoting or inhibiting interactions between subunits. Here, we correlated the ability of cyclic nucleotides to promote interactions of isolated HCN2 C-terminal domains in solution with their ability to facilitate channel opening. Cyclic IMP, a cyclic purine nucleotide, and cCMP, a cyclic pyrimidine nucleotide, bind to a C-terminal domain containing the cyclic nucleotide-binding domain but, in contrast to other cyclic nucleotides examined, fail to promote its oligomerization, and produce only modest facilitation of opening of the full-length channel. Comparisons between ligand bound structures identify a region between the sixth and seventh β strands and the distal C helix as important for facilitation and tight binding. We propose that promotion of interactions between the C-terminal domains by a given ligand contribute to its ability to facilitate opening of the full-length channel. •Facilitation of HCN2 channel opening by cAMP analogs was investigated•Some analogs bind but do not fully promote opening or C-terminal interactions•Promotion of C-terminal interactions and facilitation of opening are correlated•Ligand bound structures identify regions important for facilitation and binding Ng et al. show that direct binding of cyclic nucleotides to the HCN2 ion channel variably facilitates channel opening, and those nucleotides that are less effective openers are also unable to promote C-terminal interactions. Regions of the binding site that control facilitation and binding are identified.