Supplementary Figure 3: Crystal structures of SYCP1 αN-end (101–206) and αN-end truncated (101–175).

(a-b) Sample 2Fo-Fc electron density maps contoured at 1.2σ and superimposed on the refined crystallographic models for (a) SYCP1 αN-end (101-206) and (b) SYCP1 αN-end truncated (101-175). (c-e) Superposition of the SYCP1 αN-end (101-206) (purple) and αN-end truncated (101-175) (green) crystal structures with an rmsd of 2.28 Å. (c) Overall structural superposition (in a series of 45° rotations) reveals a similar global conformation but with a key distinction that chain B copies of αN-end splay from the midline to create an open rather than closed head-to-head assembly. (d) Close-up of the head-to-head assembly demonstrating how chain A copies of the αN-end structure adopt a similar conformation to the αN-end truncated structure, whilst chain B copies splay apart to create the open interface. (e) Cross-sections through the αN-end head-to-head open and closed interfaces. The open interface contains no hydrophobic core and is asymmetrical in nature, whereas the closed interface is formed of symmetry-related chains and contains a hydrophobic core of residues L102, L109 and I116. (f) Superposition of the two unique chains of the αN-end (101-206) structure (cyan and red) with the sole chain of the αN-end truncated (101-175) structure (blue); rmsd values between all chains are shown. Whilst αN-end chain A and αN-end truncated adopt similar conformations at the N-terminus, αN-end chain B deviates to form the open conformation. Chain A and B of αN-end further differ in angulation along the length of the dimeric coiled-coil.