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We found a novel 52 kDa matrix glycoprotein MPP1 in the shell ofCras-sostrea nippona that was unusually acidic and heavily phosphorylated. Deduced from the nucleotide sequence of 1.9 kb cDNA, which is likely to encode MPP1 with high probability, the primary structure of this protein shows a modular structure characterized by repeat sequences rich in Asp, Ser and Gly. | ỊFEBS Journal A novel phosphorylated glycoprotein in the shell matrix of the oyster Crassostrea nippona Tetsuro Samata Daisuke Ikeda Aya Kajikawa Hideyoshi Sato Chihiro Nogawa Daishi Yamada Ryo Yamazaki and Takahiro Akiyama Laboratory of Cell Biology Faculty of EnvironmentalHealth Azabu University Sagamihara Japan Keywords domain structure foliated layer oyster shell phosphorylated matrix protein poly-Asp sequences Correspondence T. Samata Laboratory of Cell Biology Faculty of EnvironmentalHealth Azabu University 1-17-71 Fuchinobe Sagamihara Kanagawa 229-0006 Japan Fax 81 42 769 2560 Tel 81 42 769 2560 E-mail samata@azabu-u.ac.jp Database The nucleotide sequences have been submitted to DDBJ with the accession number AB207821-AB207826 Received 11 January 2008 revised 31 March 2008 accepted 7 April2008 We found a novel 52 kDa matrix glycoprotein MPP1 in the shell of Cras-sostrea nippona that was unusually acidic and heavily phosphorylated. Deduced from the nucleotide sequence of 1.9 kb cDNA which is likely to encode MPP1 with high probability the primary structure of this protein shows a modular structure characterized by repeat sequences rich in Asp Ser and Gly. The most remarkable of these is the DE-rich sequence in which continuous repeats of Asp are interrupted by a single Cys residue. Disulfide-dependent MPP1 polymers occurring in the form of multimeric insoluble gels are estimated to contain repetitive locations of the anionic molecules of phosphates and acidic amino acids particularly Asp. Thus MPP1 and its polymers possess characteristic features of a charged molecule for oyster biomineralization namely accumulation and trapping of Ca2 . In addition MPP1 is the first organic matrix component considered to be expressed in both the foliated and prismatic layers of the molluscan shell microstructure. In vitro crystallization assays demonstrate the induction of tabular crystals with a completely different morphology from those formed spontaneously indicating that
