We next determined whether the association requires a significant conformational change of either of the two proteins, or it is of a rigid-body type. Superimposition of the LPHN3-OLF subunit with the P65 Ca2+-bound structure reveals an r.m.s.d. of 0.56 Å over 256 aligned Cα. The same procedure made with the FLRT3-LRR subunit with the recently determined structure (PDB ID 4V2E) (Seiradake et al., 2014) gives an overall r.m.s.d. of 1.20 Å for 321 aligned Cα, a value that falls to 0.96 Å when aligning the first 219 Cα (residues 30 to 248) which contain the main interfacing residues described earlier. This comparison indicates that the structures of LPHN3-OLF and FLRT3-LRR are rigid and undergo a rigid-body type interaction without any significant rearrangements, providing that the LPHN3-OLF is in the closed state.
