title: Identification of a novel matrix protein contained in a protein aggregate associated with collagen in fish otoliths.
abstract: In the biomineralization processes, proteins are thought to control the polymorphism and morphology of the crystals by forming complexes of structural and mineral-associated proteins. To identify such proteins, we have searched for proteins that may form high-molecular-weight (HMW) aggregates in the matrix of fish otoliths that have aragonite and vaterite as their crystal polymorphs. By screening a cDNA library of the trout inner ear using an antiserum raised against whole otolith matrix, a novel protein, named otolith matrix macromolecule-64 (OMM-64), was identified. The protein was found to have a molecular mass of 64 kDa, and to contain two tandem repeats and a Glu-rich region. The structure of the protein and that of its DNA are similar to those of starmaker, a protein involved in the polymorphism control in the zebrafish otoliths [Söllner C, Burghammer M, Busch-Nentwich E, Berger J, Schwarz H, Riekel C & Nicolson T (2003) Science302, 282-286]. (45)Ca overlay analysis revealed that the Glu-rich region has calcium-binding activity. Combined analysis by western blotting and deglycosylation suggested that OMM-64 is present in an HMW aggregate with heparan sulfate chains. Histological observations revealed that OMM-64 is expressed specifically in otolith matrix-producing cells and deposited onto the otolith. Moreover, the HMW aggregate binds to the inner ear-specific short-chain collagen otolin-1, and the resulting complex forms ring-like structures in the otolith matrix. Overall, OMM-64, by forming a calcium-binding aggregate that binds to otolin-1 and forming matrix protein architectures, may be involved in the control of crystal morphology during otolith biomineralization.
authors.affiliation: Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Japan.
authors.forename: Hidekazu
authors.initials: H
authors.lastname: Tohse
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Takagi
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Nagasawa
mesh_terms: D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry; D003094:Collagen / Q000235:genetics / Q000378:metabolism*; D007758:Ear, Inner / Q000033:anatomy & histology / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D017686:Oncorhynchus mykiss / Q000033:anatomy & histology / Q000378:metabolism; D010037:Otolithic Membrane / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D016326:Extracellular Matrix Proteins; D029941:Fish Proteins; D011993:Recombinant Fusion Proteins; C449659:otolin-1; D003094:Collagen; D002119:Calcium Carbonate