A crystal of a complex of sSortilin with a ligand; wherein the crystal is selected from the group consisting of: (a) a tetragonal crystal of sSortilin and the ligand: NGF pro domain, wherein sSortilin is a fragment consisting of SEQ ID NO.1 (amino acids 78 to 755), fused C-terminally to His6, and wherein said crystal is in space group P4 1 2 1 2 with unit cell dimension of a=b=159.97 Å, c=106.55 Å, α=β=γ=90°; (b) a tetragonal crystal of sSortilin and the ligand: peptide-4, wherein sSortilin is a fragment consisting of SEQ ID NO. 1 (amino acids 78 to 755), fused C-terminally to His6, and wherein said crystal is in space group P4 1 2 1 2 with unit cell dimensions of a=b=159.37 Å, c=108.72 Å, (α=β=γ=90°; (c) a monoclinic crystal of sSortilin and the ligand: neurotensin, wherein sSortilin is a fragment consisting of the entire luminal domain (amino acids 1 to 758) but not the transmembrane segment or the cytoplasmic tail of Sortilin, fused C-terminally to His6, and wherein said crystal is in space group C2 with unit cell dimensions of a=145.8 Å, b=74.5 Å, c=108.3 Å, α=γ=90°, β=131.87°; (d) a monoclinic crystal of sSortilin and the ligand: neurotensin, wherein sSortilin is a fragment consisting of the entire luminal domain (amino acids 1 to 758) but not the transmembrane segment or the cytoplasmic tail of Sortilin, fused C-terminally to His6, and wherein said crystal is in space group C2 with unit cell dimensions of a=162.1 Å, b=78.7 Å, c=111.1 Å, α=γ=90°, β=126.61°; and (e) a monoclinic crystal of sSortilin and the ligand: sSort-propeptide, wherein sSortilin is a fragment consisting of the entire luminal domain (amino acids 1 to 758) but not the transmembrane segment or the cytoplasmic tail of Sortilin, fused C-terminally to His6, and wherein said crystal is in space group C2 with unit cell dimensions of a=162.1 Å, b=78.1 Å, c=111.7 Å, α=γ=90°, β=127.20°. (a) a tetragonal crystal of sSortilin and the ligand: NGF pro domain, wherein sSortilin is a fragment consisting of SEQ ID NO.1 (amino acids 78 to 755), fused C-terminally to His6, and wherein said crystal is in space group P4 1 2 1 2 with unit cell dimension of a=b=159.97 Å, c=106.55 Å, α=β=γ=90°; (b) a tetragonal crystal of sSortilin and the ligand: peptide-4, wherein sSortilin is a fragment consisting of SEQ ID NO. 1 (amino acids 78 to 755), fused C-terminally to His6, and wherein said crystal is in space group P4 1 2 1 2 with unit cell dimensions of a=b=159.37 Å, c=108.72 Å, (α=β=γ=90°; (c) a monoclinic crystal of sSortilin and the ligand: neurotensin, wherein sSortilin is a fragment consisting of the entire luminal domain (amino acids 1 to 758) but not the transmembrane segment or the cytoplasmic tail of Sortilin, fused C-terminally to His6, and wherein said crystal is in space group C2 with unit cell dimensions of a=145.8 Å, b=74.5 Å, c=108.3 Å, α=γ=90°, β=131.87°; (d) a monoclinic crystal of sSortilin and the ligand: neurotensin, wherein sSortilin is a fragment consisting of the entire luminal domain (amino acids 1 to 758) but not the transmembrane segment or the cytoplasmic tail of Sortilin, fused C-terminally to His6, and wherein said crystal is in space group C2 with unit cell dimensions of a=162.1 Å, b=78.7 Å, c=111.1 Å, α=γ=90°, β=126.61°; and (e) a monoclinic crystal of sSortilin and the ligand: sSort-propeptide, wherein sSortilin is a fragment consisting of the entire luminal domain (amino acids 1 to 758) but not the transmembrane segment or the cytoplasmic tail of Sortilin, fused C-terminally to His6, and wherein said crystal is in space group C2 with unit cell dimensions of a=162.1 Å, b=78.1 Å, c=111.7 Å, α=γ=90°, β=127.20°.