Characterization and in vitro mineralization function of a soluble protein complex P60 from the nacre of Pinctada fucata

A soluble protein complex P60 from the powdered nacre of Pinctada fucata was extracted and partially characterized. The biological activity of the P60 on pre-osteoblast cell line MC3T3-E1 and bone marrow stroma cells (MSCs) was investigated. The P60 protein from the decalcified powered nacre was solubilized with acetic acid and then purified by liquid chromatography. The P60 protein was a protein complex composed of several subunits with disulfide bridges. The known protein nacrein, and its two derivatives, N28 and N35, were included in the P60 protein complex. The most abundant amino acids in the P60 that account for 68.3% of the total residues are glycine (32.1%), aspartic acid (17.4%), alanine (13.6%), and glutamic acid (5.2%). The in vitro study of the crystallization showed that this protein complex could control the formation and size of calcium carbonate. The assay of biological activity of the P60 protein complex on the pre-osteoblast cell line MC3T3-E1 and MSCs suggested that the P60 could stimulate the formation of mineralized nodules.