Examples of hydrogen bond interactions from conserved, buried arginine residues to mainchain atoms in α-helix C-terminal regions. Representative structures were chosen for each family based on resolution; residues are coloured by atom type with buried, conserved polar residues shown in magenta. Hydrogen bonds are shown in black. Two examples of arginine residues forming hydrogen bonds to C-terminal regions of α-helices from coil regions in A) the eukaryotic-type carbonic anhydrase family [PDB: 1koq] and B) the peroxidise family [PDB: 2cyp]. C) An arginine in a β-sheet forms two hydrogen bonds to a C-terminal region in the chalcone and stilbene synthases [PDB: 1i88]. D) An arginine in the N-terminal region of an α-helix forms hydrogen bonds to C-terminal regions of two helices in the annexin family [PDB: 1axn]. Two examples of arginine residues in C-terminal regions of α-helices that form hydrogen bonds to C-terminal regions in other helices in E) the cytochrome P450 s [PDB: 1jfb] and F) the cyclodextrin glycosyltransferases [PDB: 1qhp]. In the latter case a second arginine within a β-sheet also interacts with C-terminal residues of a third short helix.