Modifications on the morphology of synthetically-grown calcium oxalate crystals by crystal-associated proteins isolated from bean seed coats (Phaseolus vulgaris)

Higher plants form crystals of calcium oxalate in well-controlled conditions. This control is performed in specialized cells by an organic matrix composed by soluble and insoluble water macromolecules. The water-soluble protein matrix associated with the calcium oxalate crystals from bean seed coat (Phaseolus vulgaris) contains many polypeptides of different molecular masses. In this study, we observed that the water-soluble matrix macromolecules strongly inhibited the nucleation of calcium oxalate crystals (this inhibition was concentration dependent). Additionally, two proteins were isolated and purified from the water-soluble matrix with masses of 250 kDa called calcium oxalate macromolecule associated 1 (COMA1) and 27 kDa called calcium oxalate macromolecule associated 2 (COMA2). These proteins were also strong inhibitors of the nucleation of calcium oxalate monohydrate. On the other hand, we found that the modification in the morphology of calcium oxalate crystals due to the presence of water-soluble macromolecules (altogether) affected mainly the {1 2 0} face. Particularly, COMA1 and COMA2 separately had the same influence on the morphology of these crystals.