Examples of hydrogen bond interactions from conserved, buried residues to mainchain atoms in 3
helices. Representative structures were chosen for each family based on resolution; residues are coloured by atom type with buried, polar residues shown in magenta. Hydrogen bonds are shown in black. A) Two arginines in the cyclodextrin glycosyltransferases family which hydrogen bond to two 310 helices [PDB: 1d3c]. B) A tryptophan that forms a hydrogen bond to a 310 helix in the papain family cysteine proteinases [PDB 1mem]. C) Two aspartates that form a hydrogen bond to each other's respective mainchain amide atom group in a 310 helix in the pancreatic lipases [PDB: 1bu8]. D) A cysteine forms a hydrogen bond with a 310 helix in the aldehyde oxidase and xanthine dehydrogenase family (domains 1&2) [PDB: 1n62] E) Three cysteines that form a complex with an iron sulphate (4Fe-4S) cluster also form hydrogen bonds to 310 helices that form the binding site [PDB: 1e3d]. F) A tyrosine within a central strand forms a hydrogen bond to a mainchain carbonyl within a 310 helix in the immunoglobulin domain (V set) family [PDB 2rhe].