title: Molecular analyses of protein components of the organic matrix in the exoskeleton of two scleractinian coral species.
abstract: Biochemical and histological studies on the exoskeleton of scleractinian corals had demonstrated presence of the organic matrix containing proteins, lipids and chitin. Examination at the electron microscopic level had shown that the initial phase of calcification occurred in close association with organic substances secreted by calicoblastic cells. The possibility was thereby proposed that certain organic substances induce formation of calcium carbonate crystals, presumably functioning as templates for nucleation. In search for such a molecule, biochemical and molecular analyses were initiated on protein components of the organic matrix extracted from the calcified exoskeleton of the hermatypic coral, Galaxea fascicularis and the ahermatype, Tubastrea aurea. In SDS-PAGE analyses of the extracts, one major protein and a few other minor bands were detected in each of the two species. A cDNA encoding the major protein (named galaxin) in G. fascicularis was cloned and its primary structure was deduced. It consisted mostly of tandem repeats of a unit sequence of about 30 residues, and its sequence did not exhibit significant similarity to known proteins. Preliminary characterization of the T. aurea proteins showed that two proteins bound Ca(2+), and suggested that the major protein of 46 kDa was not homologous to galaxin.
authors.affiliation: Division of Marine Bioscience, Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan. toshi@ori.u-tokyo.ac.jp
authors.forename: Toshiki
authors.initials: T
authors.lastname: Watanabe
authors.forename: Isao
authors.initials: I
authors.lastname: Fukuda
authors.forename: Katsunori
authors.initials: K
authors.lastname: China
authors.forename: Yeishin
authors.initials: Y
authors.lastname: Isa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D037421:Anthozoa / Q000033:anatomy & histology* / Q000737:chemistry* / Q000145:classification; D002113:Calcification, Physiologic; D004591:Electrophoresis, Polyacrylamide Gel; D008969:Molecular Sequence Data; D011506:Proteins / Q000032:analysis* / Q000737:chemistry*; D020449:Repetitive Sequences, Amino Acid; D012995:Solubility
chemical_list: D011506:Proteins