Fig. 4

Binding of PEG and crown ether to lysine. The PEG fragments are shown as thick stick models in pink, and the lysine side chains as thin sticks in green and cyan for the heavy and light chains. The identity of ligands and the lysine residues are indicated on the top and at the bottom of each panel. In (a) and (b) the alternate binding modes to the same lysine side chain formed a closed ring structure, even though there was no crown ether in the 3.3-Fab crystal. In (c) the PEG fragment bound to the same lysine in another 3.3-Fab is more open. In (d) a real crown ether is bound to the equivalent lysine in the 2B5-Fab crystal. In (e) – (h) each lysine has crown ether bound in a similar mode