In both crystal forms, the crystallized LPHN3-OLF construct polypeptidic chain was built in their respective electron density maps except from its N-terminal (linker, FLAG tag and Lys199) and C-terminal (463–495 and the 3C Protease residual recognition motif) fragments, as well as the loop 392–405 which could not be entirely modeled due to the lack of reliable definition of the position by the electron density maps for several residues (i.e. fragments 395–403 and 397–403 absent in the C2221 and the P65 form, respectively) (Table S1, related to Figure 2). Consistently, those three fragments are shown to be among the highest solvent-exposed portions of the protein by DXMS experiment (see below). The peptide 395-YEDDDNEAT-403 is most likely highly solvated on the five negatively charged Asp and Glu residues clustered in this small nine-residue fragment on the surface of the protein. As for the N- and C-terminal fragments, they likely have undergone cleavage during the crystallization process, as we found that the form of the protein that provided suitable crystals was shorter than the one present in freshly purified preparations used for AUC
