title: Identification and characterization of a matrix protein (PPP-10) in the periostracum of the pearl oyster, Pinctada fucata.
abstract: The periostracum is a layered structure that is formed as a mollusk shell grows. The shell is covered by the periostracum, which consists of organic matrices that prevent decalcification of the shell. In the present study, we discovered the presence of chitin in the periostracum and identified a novel matrix protein, Pinctada fucata periostracum protein named PPP-10. It was purified from the sodium dodecyl sulfate/dithiothreitol-soluble fraction of the periostracum of the Japanese pearl oyster, P. fucata. The deduced amino acid sequence was determined by a combination of amino acid sequence analysis and cDNA cloning. The open reading frame encoded a precursor protein of 112 amino acid residues including a 21-residue signal peptide. The 91 residues following the signal peptide contained abundant Cys and Tyr residues. PPP-10 was expressed on the outer side of the outer fold in the mantle, indicating that PPP-10 was present in the second or third layer of the periostracum. We also determined that the recombinant PPP-10 had chitin-binding activity and could incorporate chitin into the scaffolds of the periostracum. These results shed light on the early steps in mollusk shell formation.
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Nakayama
authors.forename: Michio
authors.initials: M
authors.lastname: Suzuki
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Endo
authors.forename: Kurin
authors.initials: K
authors.lastname: Iimura
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Kinoshita
authors.forename: Shugo
authors.initials: S
authors.lastname: Watabe
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kogure
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Nagasawa
keywords: Biomineralization; Chitin; DOPA, 3,4-dihydroxyphenylalanine; DTT, dithiothreitol; HPLC, high performance liquid chromatography; Matrix protein; PPP, Pinctada fucata periostracum protein; Periostracum; Pinctada fucata; SDS, sodium dodecyl sulfate