Examples of hydrogen bond interactions from conserved, buried residues to mainchain atoms in edge strands. 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 arginine in the peroxidases which forms hydrogen bonds to an edge strand [PDB: 1qpa]. B) An example of asparagine forming a hydrogen bond to a strand in a β-barrel (classified as edge strands) in the xylose isomerise family [PDB: 1bxb]. C) A cysteine forms a hydrogen bond with a strand in a β-sheet in the Zinc-binding domain present in Lin-11, Isl-1, Mec-3 protein family [PDB: 1a7i]. Two examples of threonines forming hydrogen bonds to edge strands in D) the pyridine nucleotide-disulphide oxidoreductases (class 1) [PDB: 3grs] and E) the aldehyde oxidase and xanthine dehydrogenase (domains 3&4) family [PDB: 1n62]. F) A tyrosine in cyclodextrin glycosyltransferases forms a hydrogen bond to an edge strand [PDB: 1qhp].