Packing modes of 3₁₀ helices. (A) Mode A. Two views of the packing of a 10-residue-long 3₁₀ helix (in red) in glycogen phosphorylase (Protein Data Bank accession no. 1GPB). The rest of the protein is shown as blue surface. (B) Mode B. Two views of packing of a 10-residue-long 3₁₀ helix (in red) in dienelactone hydrolase (Protein Data Bank accession no. 1DIN). Two phenylalanine residues, shown as green CPK spheres, interact with the face of the 3₁₀ helix. Other protein regions are shown as a blue cartoon. (C) Bar graph showing percentage of solvent-accessible surface area for each of the 3₁₀ helices identified. Black bars indicate helices in packing mode A. Protein Data Bank accession numbers and residue numbering of respective 3₁₀ helices: 1TAG, 201–208; 3SDH, 44–51; 1GPB, 515–524; 1PZ4, 95–103; 1OBO, 1040–1047; 1GS6, 405–412; 1H1N, 180–186; 1LRV, 172–178 (1LRV is a leucine-repeat protein with a 3₁₀ helix present in each repeat; we have only considered one repeat in our analysis). Gray bars indicate helices in packing mode B. Protein Data Bank accession numbers and residue numbering of respective 3₁₀ helices: 1TYS, 134–140; 1CEO, 241–248; 1DIN, 150–158; 1PZ4, 104–110. Empty bar indicates the fully encased 3₁₀ helix (8ACN, 168–174).