In Vitro Regulation of CaCO₃Crystal Growth by the Highly Acidic Proteins of Calcitic Sclerites in Soft Coral,Sinularia Polydactyla

Abstract

Acidic proteins are generally thought to control mineral formation and growth in biocalcification. Analysis of proteinaceous components in the soluble and insoluble matrix fractions of sclerites in Sinularia polydactyla indicates that aspartic acid composes about 60% of the insoluble and 29% of the soluble matrix fractions. We previously analyzed aspartic acids in the matrix fractions (insoluble = 17 mol%; soluble = 38 mol%) of sclerites from a different type of soft coral, Lobophytum crassum, which showed comparatively lower aspartic acid-rich proteins than S. polydactyla. Thus, characterization of highly acidic proteins in the organic matrix of present species is an important first step toward linking function to individual proteins in soft coral. Here, we show that aspartic-acid rich proteins can control the CaCO(3) polymorph in vitro. The CaCO(3) precipitates in vitro in the presence of aspartic acid-rich proteins and 50 mM Mg(2+) was verified by Raman microprobe analysis. The matrix proteins of sclerites demonstrated that the aspartic-acid rich domain is crucial for the calcite precipitation in soft corals. The crystalline form of CaCO(3) in the presence of aspartic acid-rich proteins in vitro was identified by X-ray diffraction and, revealed calcitic polymorphisms with a strong (104) reflection. The structure of soft coral organic matrices containing aspartate-rich proteins and polysaccharides was assessed by Fourier transform infrared spectroscopy. These results strongly suggest that the aspartic acid-rich proteins within the organic matrix of soft corals play a key role in biomineralization regulation.

First evidence of chitin in calcified coralline algae: new insights into the calcification process of Clathromorphum compactum

“…The spectrum reveals two peaks at 2527 and 1799 cm −1 which in shape and position are evidence for the presence of calcite31. Two strong Mg-calcite bands at 718 cm −1 (v4) and 873 cm −1 (v2) were also identified by FTIR32. The main chitin bands in the bulk skeletal structural crystalline side were amide A (3427 cm −1 ), amide B (2962 cm −1 ), amide I & II (1456 cm −1 ), and the amide III (1262 cm −1 ).…”

Biotic Control of Skeletal Growth by Scleractinian Corals in Aragonite–Calcite Seas

“…Galaxin possesses small acidic domains since the Asx (aspartate plus asparagine) fraction in the galaxin is 9.7% [19]. The aspartic acid-rich proteins within the organic matrices of soft corals play a key role in calcitic crystal formation [21]. Organic matrices with acidic domains, including the Asx fraction, may facilitate formation of a calcite skeleton in scleractinian corals.…”

An Overview of the Medical Applications of Marine Skeletal Matrix Proteins

“…However, due to the lack of effective extraction/analytical methods, the applications of these potential resources for drugs are comparatively fewer than for other marine organisms. Recently, we perceived protein induced crystallization [ 2 , 7 , 8 , 12 , 13 ], which showed potential crystal design and growth that could help medicinal chemistry in drug design. Our primary chemical proteomic results from soft coral revealed a number of molecules with high concentrations [ 5 , 14 ].…”

“…Organic matrices have the advantage of being naturally produced, retaining the native, functional conformation of the original proteins. Moreover, a significant number of calcifying marine invertebrates produce polysaccharides within their extracellular matrices and connective tissues [ 7 , 8 ] that have molecular structures and functions similar to human versions [ 1 , 6 ]. Polysaccharides derived from marine invertebrate extracellular matrices encompass an enormous variety of structures and should be considered as an extraordinary source of biochemical diversity.…”