Prt/ZP domain, predicted binding. (A) Prt/ZP2 (ZP domain) model; (B) Prt/ZP3(ZP domain) model; (C) Prt/ZP4(ZP domain) model. ZP domains and Prt are shown respectively in surface and cartoon representations. N-terminal region of ZP domain is coloured in yellow-orange. C-terminal region of ZP domain is coloured in pale cyan. Expected Internal Hydrophobic Patch (IHP) interdomain linker (using the mouse and human IHP linkers as templates; as described in Jovine et al. ), are coloured in magenta. Polar contacts with corresponding ZP amino acids are indicated with one-letter code. Based on UniProtKB/Swiss-Prot sequences [Prt (A4ULE2); ZP2 (Q9BH10; a.a. 366–632); ZP3(P48830; a.a. 44–306); ZP4(Q9BH11; a.a. 188–465)].