Examples of hydrogen bond interactions from conserved, buried residues within edge strands to mainchain atoms. 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. A) An asparagine forms hydrogen bonds to mainchain atoms in a type IV β-turn in aspartate/ornithine carbamoyltransferases [PDB: 1oth]. Within the cyclodextrin glycosyltransferases [PDB: 1qhp] B) an asparagine forms hydrogen bonds to mainchain atoms within a complicated β-hairpin structure (strands and hairpin shown in purple). C) A tryptophan forms hydrogen bonds to a turn joining two β-strands in the cyclodextrin glycosyltransferases [PDB: 1qhp]. D) Histidine forming hydrogen bonds to a 310 helix in the Cu/Zn superoxide dismutase family [PDB: 2aps]. Two examples of glutamine residues forming hydrogen bonds to mainchain atoms in another strand within a β-sandwich in E) the picornavirus coat protein family (also forms hydrogen bonds to mainchain atoms within a 310 helix and coil region) [PDB: 2plv] and F) the immunoglobulin domain (V set) light chain family [PDB: 6fab].