Studies on two closely related species of octocorallians: biochemical and molecular characteristics of the organic matrices of endoskeletal sclerites.

Two species of alcyonarian corals, Lobophytum crassum and Sinularia polydactyla, are closely related to each other. It is reported that the calcified organic substances in the skeletons of both contain a protein-polysaccharide complex playing a key role in the regulation of biocalcification. However, information on the matrix proteins of endoskeletal sclerite has been lacking. Hence we studied the proteinaceous organic matrices of sclerites for both species, to analyze the sequences and the functional properties of the proteins present. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the preparations showed four bands of proteins with apparent molecular masses of 102, 67, 48, and 37 kDa for L. crassum and seven bands of 109, 83, 70, 63, 41, 30, and 22 kDa for S. polydactyla. A major protein band of about 67 kDa in L. crassum and two bands of proteins of about 70 and 63 kDa in S. polydactyla yielded N-terminal amino acid sequences. Periodic acid-Schiff staining indicated that the 67-kDa protein in L. crassum, and 83- and 63-kDa proteins in S. polydactyla were glycosylated. For detection of calcium binding proteins, a Ca(2+) overlay analysis was conducted in the extract via (45)Ca autoradiography. The 102- and 67-kDa calcium binding proteins in L. crassum, and the 109- and 63-kDa Ca(2+) binding proteins in S. polydactyla were found to be radioactive. An assay for carbonic anhydrase (CA), which is thought to play an important role in the process of calcification, revealed specific activities. Newly derived protein sequences were subjected to standard sequence analysis involving identification of similarities to other proteins in databases. The significantly different protein expressions and compositional analysis of sequences between two species were demonstrated.