CRYSTALLIZATION OF SEED GLOBULINS FROM LEGUMES

Seeds contain large quantities of proteins and are therefore main food sources. In the last century, protein extracts of legume seeds were d ialysed against distilled water and in some cases small crystals of pu re protein appeared. However, those crystals were generally of poor qu ality with respect to X-ray diffraction. Recently, the crystallization of some of them was improved and the structures of two 7S globulins, phaseolin from Phaseolus vulgaris and canavalin from Canavalia ensifor mis, have been determined at 3.0 and 2.6 angstrom resolution, respecti vely. Efforts to improve the quality of the phaseolin crystals resulte d in three new crystal forms which will be discussed in this paper. Th e only high-resolution X-ray analysis of a seed globulin from legumes is that of narbonin, a 2S protein from Vicia narbonensis. The crystal structure at 1.8 angstrom shows a very compact packing in layers of mo lecules. The intermolecular contacts include salt bridges and hydropho bic clusters that might facilitate both the aggregation of the molecul es and their crystallization. Because the seed globulins appear in lar ge quantities in the protein bodies of the seeds, efficient packing of the molecules similar to the crystal packing can be assumed.