Crystallization and preliminary X-ray analysis of lectin C from the roots of pokeweed (Phytolacca americana).

Lectin C from the roots of pokeweed (Phytolacca americana) (PL-C; 13 747 Da, 126 amino-acid residues), which consists of three chitin-binding domains, was initially crystallized in two crystal forms. One form, obtained in the presence of 30%(w/v) PEG 4000, belongs to the tetragonal system. The other, obtained in the presence of 2.0 M ammonium sulfate, belongs to the rhombohedral system. Statistical analyses of the X-ray diffraction intensities showed that both crystals were twinned. Single crystals suitable for a diffraction experiment were obtained by the addition of 0.5%(v/v) dioxane to the latter precipitant solution. They belong to space group R3, with unit-cell parameters a = b = 104.1, c = 69.7 A, and diffract X-rays to 1.8 A resolution. A heavy-atom derivative crystal has been obtained and structure determination is presently ongoing using the SIRAS method.