CRYSTALLIZATION AND PRELIMINARY X-RAY DIFFRACTION STUDY OF TRICHOSANTHES KIRILOWII LECTIN. Yao-Ping Wang, Ji-Shen Pan, Ke-Yi Wang^#, Ru-Chang Bi. Institute of Biophysics, Academia Sinica, Beijing 100101, P.R.China; ^#Institute of Biochem., Academia Sinica, Shanghai 200031, P.R.China

Trichosanthes Kirilowii lectin(TKL) is a new protein purified from a Chinese herb medicine, the tuber of Trichosanthes Kirilowii maxim. It consists of two peptide chains, each with approximately 30kD molecule weight. TKL has diverse biochemistry, physiology and toxicology activities and binds strongly with galactose and lactose. It shows immunological cross-reactions with both ricin contained in seeds of Ricinus communis and trichosanthin, another interesting protein from Trichosanthes Kirilowii maxim with anti-AIDS effects. There is high structural similarity between the A-chain of ricin and trichosanthin. It is important to determine TKL structure and to compare the structural aspects of TKL, ricin and trichosanthin in elucidating the structure-function relationships of these proteins at molecular level.

After screening of crystallization conditions with the conventional hanging- drop method, better TKL crystals appeared under the following conditions: a drop prepared by mixing 2ul sample solution with concentration of 8.3mg/ml TKL and 2ul reservoir solution, equilibrated against 500ul reservoir solution, containing 0.5M Li₂SO₄ and 15% PEG-8000. The crystals belong to an orthogonal space group with unit cell parameters of a=44.7 Å, b=69.5 Å and c=180.9 Å, and there is one molecule in the asymmetric unit. 3 Å diffraction data were collected at room temperature, using Mar Research Image Plate System in our laboratory.