Purification, crystallization and preliminary X-ray analysis of a water-soluble chlorophyll protein from Brassica oleracea L. var. acephala (kale)

A water-soluble chlorophyll protein (WSCP) with a chlorophyll a:b ratio of 6:1 from Brassica oleracea L. var. acephala (kale) was purified and crystallized by the hanging-drop vapour-diffusion method using PEG 8000 and zinc acetate as precipitants. The crystal belongs to the hexagonal space group P6(4)22, with unit-cell parameters a = b = 162.2, c = 38.7 Angstrom. A native data set was collected to 2.80 Angstrom resolution at 293 K using Cu Kalpha radiation from a rotating-anode generator. Preliminary analysis via molecular replacement identified one kale WSCP monomer in the asymmetric unit. The crystal packing showed a tetrameric structure for kale WSCP, as suggested by previous biochemical studies of WSCPs from Brassicaceae plants.