1. A crystal of a polypeptide consisting of the amino acid sequence of residues 33-766 of SEQ ID NO: 2 and a polyhistidine tag added to the C-terminal end thereof wherein the crystal has a space group of P2 1 2 1 2 1 with unit cell parameters of a=118.0±5.0 Å, b=125.9±5.0 Å, c=136.8±5.0 Å, and α=β=γ=90°, and said crystal diffracts X-rays for the determination of the atomic coordinates of the polypeptide at a resolution of 3 Å or better.