Figure 9.

Examples of hydrogen bond interactions from conserved, buried residues to mainchain atoms in 3₁₀ 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].