Rahman M Azizur, Isa Y, Takemura A, Uehara T
Department of Marine and Environmental Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara-cho, Okinawa 903-0213, Japan.
Calcif Tissue Int. 2006 Mar;78(3):178-85. doi: 10.1007/s00223-005-0253-y. Epub 2006 Mar 8.
The mesoglea of alcyonarians is occupied by an abundance of minute calcitic sclerites. The sclerites of the alcyonarian Lobophytum crassum contain a water-soluble organic matrix comprising 0.48% of the sclerite weight and a water-insoluble fraction comprising 1.15% of the sclerite weight. Analysis of proteinaceous components in the soluble fraction shows a particularly high content of aspartic acid, followed by alanine, glycine, and glutamate. Aspartic acid, glycine, alanine, and glutamate are the most abundant residues in the insoluble fraction. In both cases, the fractions show the highest concentration of aspartic acid from the total proteins. In an in vitro assay, we show that the matrix proteins extracted from the calcitic sclerites induce the formation of amorphous calcium carbonate prior to its transformation into the calcitic crystalline form. We also show scanning electron micrographs of the rhombohedral calcite crystals used as template, the protein imprinted with these crystals. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of both matrices shows the protein fractions at 67 and 48 kDa. The soluble matrix shows two additional faint bands. Both fractions stain for a carbohydrate at 67 kDa, indicating a glycoprotein at this molecular weight. A newly derived protein sequence was subjected to bioinformatics analysis involving identification of similarities to other acidic proteins. The identification of these proteins in alcyonarian endoskeletal sclerites emphasizes the fundamental importance of such acidic proteins and sheds more light on the functions of these proteins in the processes of biocalcification.
软珊瑚的中胶层中充满了大量微小的方解石骨针。软珊瑚厚叶短指软珊瑚的骨针含有一种水溶性有机基质，占骨针重量的0.48%，还有一种水不溶性部分，占骨针重量的1.15%。对可溶部分蛋白质成分的分析表明，天冬氨酸含量特别高，其次是丙氨酸、甘氨酸和谷氨酸。天冬氨酸、甘氨酸、丙氨酸和谷氨酸是不溶部分中含量最丰富的残基。在这两种情况下，这些部分中天冬氨酸在总蛋白质中的浓度最高。在体外试验中，我们表明从方解石骨针中提取的基质蛋白在其转化为方解石晶体形式之前诱导无定形碳酸钙的形成。我们还展示了用作模板的菱形方解石晶体的扫描电子显微镜照片，以及印有这些晶体的蛋白质。两种基质的十二烷基硫酸钠-聚丙烯酰胺凝胶电泳显示蛋白质条带分别在67 kDa和48 kDa处。可溶基质还显示出另外两条 faint 条带。两种部分在67 kDa处均对碳水化合物染色，表明该分子量处存在糖蛋白。对一个新推导的蛋白质序列进行了生物信息学分析，包括鉴定与其他酸性蛋白质的相似性。在软珊瑚内骨骼骨针中鉴定出这些蛋白质，强调了此类酸性蛋白质的根本重要性，并为这些蛋白质在生物矿化过程中的功能提供了更多线索。
