LPHN3-OLF crystallized in two lattices – P65 and C2221. The major difference in the crystallization conditions was in the range of concentration of MgCl2 used (either 50 for the P65 form or 300 mM for the C2221 form, see Methods). When superimposed, the structures refined from the two lattices were very similar (r.m.s.d = 0.9 Å, 243 aligned Cα out of 254), with the exception of the loop 316–329 which is stabilized by the protein core in the P65 lattice (“closed” conformation) and projecting towards a symmetric neighbor in the C2221 lattice (“open” conformation) (Figure 2B). In the open state, this loop is highly flexible as illustrated by a dramatic increase of its thermal motion (B-factors), as compared to the rest of the protein and the closed conformation (Figure 2C). Indeed, the position of the loop in the open conformation was weakly defined by the electron density maps. Accompanying the movement of loop 316–329, two other neighboring loops (392–405 and 425–434) undergo a noticeable conformational change (Figure 2B). Interestingly, loop 392–405 includes the unmodeled fragment 397–403.
