Table 1. Overview of PDB-IDs of Channels, Sequence Regions of Closed Gaps in Loop Regions, CNBD Residues, and Residues Designated as Ligand-Binding Residues within the CNBD.

PDB-ID	identifier	closed gaps	CNBD residues	ligand-binding residues
5U6O	apo HCN1, closed	201–202, 243–251	466–585	503, 522, 527,530, 532, 537–545, 548–553
5U6P	holo HCN1, closed			503, 522, 527,530, 532, 537–545, 548–553
6GYN	apo HCN4, closed		593–706	624, 643, 645, 651, 653, 658–664, 669–674
6GYO	holo HCN4, closed
7NP3	apo HCN4, open			624, 632, 643, 645, 651, 653, 658–664, 669–672, 674
7NP4	holo HCN4, closed
6WEJ	apo TAX4, closed	162–164	593–706	521, 527, 529, 540, 549, 550, 552, 557–563, 574–579, 616, 617
6WEK	holo TAX4, open	161–166
6V1X	KAT1, closed	158–160	374–491	405, 413, 426, 428, 436, 438, 443–449, 454–457, 459