Examples of hydrogen bond interactions from conserved, buried residues in centre 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. Examples of coils that are supported by hydrogen bonds from polar residues at the end of central strands, including A) an aspartate in the aldehyde oxidase and xanthine dehydrogenases (domains 3&4) [PDB: 1n62], two glutamates in B) the alcohol dehydrogenases [PDB: 2ohx] and C) the isocitrate and isopropylmalate dehydrogenases [PDB: 1cnz] and D) an arginine in the serine proteinase inhibitor family [PDB: 1hle]. E) A tyrosine residue in the pancreatic lipase family forms a hydrogen bond with a type IV β-turn [PDB: 1bu8]. Two cases where mainchain atoms in helices are satisfied by hydrogen bonds from F) an asparagine in eukaryotic-type carbonic anhydrases [PDB: 1koq] and G) a glutamate in the NADH ubiquinone oxidoreductases. Examples of mainchain atoms in β-barrel strands that are satisfied by hydrogen bonds from H) an aspartate in PDZ domain proteins [PDB code 1be9] and I) a serine in the aldo/keto reductases [PDB: 1ads].