| The abalone shell is a microlaminate organic-inorganic composite of mineral and biopolymers exhibiting exceptional nanoscale regularity and a strength 3000 times greater than that of the inorganic crystals. A series of experiments were conducted to investigate the characteristics of both inorganic component and organic matrix in the shell of Haliotis discus hannai Ino. Further more, in vivo (shell repair, flat pearl) and in vitro systems were undertaken to better understand the biomineralization processes of abalone shell. The results are summarized as follows:The internal shell structure of Haliotis discus hannai Ino was studied using scanning electron microscopy. The shell consists of the periostracum, prismatic and nacreous layers with calcite in the outer prismatic layer and aragonite in the inner nacreous layer. FTIR analysis of the prismatic powder showed characteristic spectra of calcite: 876cm-1 (v2) and 710cm-1 (v4), whereas aragonitic nacreous layer with characteristic spectra of 858 cm-1 (v2) and 712-700cm-1 (v4). Another absorption area in the range 2520-2650 cm"1 in both the nacre powder and the prismatic powder was assigned to HCO3 ~ groups resided in the mineral or at the organic mineral interface, which suggested a potential participation of HCO3 ~ groups in shell formation as an intermediate.Biochemical characterization of organic matrix from shell of Haliotis discus hannai Ino was performed by the combination of amino acid composition analysis, SDS-PAGE and Fourier Transform Infrared spectrum techniques. Results of amino acid analyses indicated a high content of Asx, Gly and Glx in the soluble matrix, which account to 70% (mol %) of the total amino acid. While the amino acid composition of the insoluble matrix shows a different profile, dominating by Gly, Ala, Ser and hydrophobic amino acid residues, which indicate strong similarity to the spider dragline silk. From the FTIR spectra, we infer that a major portion of the soluble matrix adopt the a-helix conformation, while most of the insoluble matrix is in the a-helix conformation with a medium band indicating p-sheet conformation. Gel electrophoresis revealed that the soluble fraction from whole shell is composed of at least nine major proteins/peptides, ranging in size from 14 to over 66 kD, while only three proteins/peptides are detected in the nacreous soluble matrix. In addition, preliminary studies on the dissolution of proteins/peptides from insoluble matrix were conducted. For the insoluble matrix of whole shell, at least three proteins/peptides, with apparent molecular mass of 12kD, 14 kD and 38.6 kD, were dissolved, and only one 38.6 kD protein/peptide was solubilized from the insoluble matrix of nacre layer. However, the macromolecules extracted from Haliotis discus hannai Ino share certain important biochemical properties with that from other mineralized tissues: unusually acid proteins rich in aspartic acid and proteins/peptides that have partially adopted thea-helix or p-sheet conformation.In addition, the correspondence between crystal phase and soluble matrix with different origins is studied with in vitro crystallization experiment. It is found that soluble matrix with different origins have specialties to induce different crystals with special morphologies: soluble matrix isolated from the prismatic layer was shown to induce calcite formation in vitro, yielding globular or spindle-shaped growth instead of the rhombohedra obtained in the absence of proteins; while soluble matrix isolated from the nacreous layer induces almost symmetrical hedgehog-like aragonitic aggregates formation. It has been accepted that the formation, morphological development and crystallography of minerals are controlled by the intrinsic molecular recognition of macromolecules for specific molecular motifs exposed on certain crystal plane. To understand the underlying mechanisms of the protein-mineral interactions, it seems essential first of all to know the primary structure of the soluble matrix involved.The difficulty of analyzing biom... |
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