Figure 1

Polypeptide conformations. Stick pictures show main chain atoms of polypeptides; side chains are omitted; colors: carbon, green; oxygen, red; iron, rust; nitrogen blue; phosphorus, orange; sulphur, yellow; nickel, brown; potassium, purple. a) α-helix b) β-strand, as in i c) polyproline type II helix d) RL nest e) phosphate bound to LRLR nest f) Fe₃S₄ bound to RLRLR nest g) α-strand, as in l h) Nickel-tetraglycine [62] i) β-sheet j) A row of potassium ions bound at the selectivity filter of the potassium channel; only two of the four polypeptides are shown. k) A row of waters (hydrogens not shown) bound to part of the aquaporin channel l) α-sheet, made from strands as in g, a possible early membrane.