(A) MST1 forms two non-polar strands arranged as a double helix. Repeating units of MST1 are visualized here with the immunoglobulin-like domains and the poly(proline) helix hidden to better display the strand-like architecture of the cysteine-rich domains. The boxes indicate the regions shown in (B)–(D).
(B) The fundamental repeat unit of the mastigoneme is an antiparallel MST1 homodimer. Only the cysteine-rich domains are shown for clarity.
(C) Intrastrand interactions between the C-terminal ends of cysteine-rich domains from adjacent homodimers. Interacting residues, which are predominantly hydrophobic, are labeled.
(D) The C terminus of the poly(proline) type II (PPII) helix binds near the interstrand interface between neighboring cysteine-rich domains. The box indicates the region shown in detail in (E).
(E) Details of the interactions between the C terminus of MST1 and the interstrand interface. See also Figure S1.