An iron-sulfur cluster: 4Fe4S

This is from an FeS protein involved in the electron transport chain. The 4 Fe atoms are ligated by 4 S^- ions and by 4 Cys sulfides. Fe are colored brown, and sulfides are colored yellow, and are all shown in spacefilling. The protein is shown in wireframe. Three of the Cys are close in sequence, here i, i+3, i+6, while the 4th is about 50 aa residues away.

A zinc finger

This is from a DNA binding protein. The zinc is playing a structural role. It is ligated by 2 cysteine residues (S) and 2 histidine residues (N). The histidine residues come from the C-terminus of an alpha-helix (with nitrogens blue), and the cysteine residues come from the loop of a short beta-hairpin (with sulfur atoms colored yellow). The secondary structures are shown in cartoons (colored by structure). The zinc is colored violet.