title: A novel acidic matrix protein, PfN44, stabilizes magnesium calcite to inhibit the crystallization of aragonite.
abstract: Magnesium is widely used to control calcium carbonate deposition in the shell of pearl oysters. Matrix proteins in the shell are responsible for nucleation and growth of calcium carbonate crystals. However, there is no direct evidence supporting a connection between matrix proteins and magnesium. Here, we identified a novel acidic matrix protein named PfN44 that affected aragonite formation in the shell of the pearl oyster Pinctada fucata. Using immunogold labeling assays, we found PfN44 in both the nacreous and prismatic layers. In shell repair, PfN44 was repressed, whereas other matrix proteins were up-regulated. Disturbing the function of PfN44 by RNAi led to the deposition of porous nacreous tablets with overgrowth of crystals in the nacreous layer. By in vitro circular dichroism spectra and fluorescence quenching, we found that PfN44 bound to both calcium and magnesium with a stronger affinity for magnesium. During in vitro calcium carbonate crystallization and calcification of amorphous calcium carbonate, PfN44 regulated the magnesium content of crystalline carbonate polymorphs and stabilized magnesium calcite to inhibit aragonite deposition. Taken together, our results suggested that by stabilizing magnesium calcite to inhibit aragonite deposition, PfN44 participated in P. fucata shell formation. These observations extend our understanding of the connections between matrix proteins and magnesium.
authors.affiliation: From the Institute of Marine Biotechnology, School of Life Sciences and.
authors.forename: Cong
authors.initials: C
authors.lastname: Pan
authors.forename: Dong
authors.initials: D
authors.lastname: Fang
authors.forename: Guangrui
authors.initials: G
authors.lastname: Xu
authors.forename: Jian
authors.initials: J
authors.lastname: Liang
authors.forename: Guiyou
authors.initials: G
authors.lastname: Zhang
authors.forename: Hongzhong
authors.initials: H
authors.lastname: Wang
authors.forename: Liping
authors.initials: L
authors.lastname: Xie
authors.forename: Rongqing
authors.initials: R
authors.lastname: Zhang
mesh_terms: D000143:Acids / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002119:Calcium Carbonate / Q000737:chemistry / Q000378:metabolism*; D019295:Computational Biology; D003460:Crystallization; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D060734:Nacre / Q000737:chemistry / Q000378:metabolism; D049911:Pinctada / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000143:Acids; D016326:Extracellular Matrix Proteins; D060734:Nacre; C005479:magnesium carbonate; D002119:Calcium Carbonate; D008274:Magnesium; D002118:Calcium
keywords: Biomaterials; Biomineralization; Cloning; Extracellular Matrix Proteins; Protein Chemistry