Proteomic analysis of skeletal organic matrix from the stony coral Stylophora pistillata

Abstract

It has long been recognized that a suite of proteins exists in coral skeletons that is critical for the oriented precipitation of calcium carbonate crystals, yet these proteins remain poorly characterized. Using liquid chromatography-tandem mass spectrometry analysis of proteins extracted from the cell-free skeleton of the hermatypic coral, Stylophora pistillata , combined with a draft genome assembly from the cnidarian host cells of the same species, we identified 36 coral skeletal organic matrix proteins. The proteome of the coral skeleton contains an assemblage of adhesion and structural proteins as well as two highly acidic proteins that may constitute a unique coral skeletal organic matrix protein subfamily. We compared the 36 skeletal organic matrix protein sequences to genome and transcriptome data from three other corals, three additional invertebrates, one vertebrate, and three single-celled organisms. This work represents a unique extensive proteomic analysis of biomineralization-related proteins in corals from which we identify a biomineralization “toolkit,” an organic scaffold upon which aragonite crystals can be deposited in specific orientations to form a phenotypically identifiable structure.

Temporal and spatial expression patterns of biomineralization proteins during early development in the stony coral Pocillopora damicornis

“…Although the role of galaxin in biomineralization remains unresolved, the protein shows sequence similarity to usherin, a type IV collagen binding protein. Type IV collagen is also found in the coral skeleton [16,17] and four orthologues of collagen IV Figure 5. Summary of the major findings of our study on gene differential expression (DE) and protein immunolocalization during early development in P. damicornis.…”

“…In addition, the coral proteome is composed of paralogues of adhesion, structural and functional proteins. The fact that 11 proteins were previously reported to be part of the biomineralization toolkit [16,17] and the encoding genes are upregulated in stage III, suggests that corals co-opt pre-existing genes for biomineralization. The novel characterization of the temporal and spatial pattern of SOM proteins presented here (figure 5) illuminates the timeline and key players in a critical biological function, biomineralization.…”

“…This dataset was mean centred and clustered (hclust package in R) to identify expression patterns conserved across the life stages. A more comprehensive annotation of SOM structural proteins was completed based on previous proteomic analysis of coral SOM [16].…”

“…The rationale for this approach was that the soluble fraction of the SOM is known to be rich in acidic amino acids [6,29,30] and five CARPs have been suggested to play a major role in calcium carbonate nucleation [16,18]. This dataset was clustered (hclust package in R) to identify expression patterns conserved across the life-history stages that may be important in organizing and promoting calcification within the organic matrix.…”

Immunolocalization of skeletal matrix proteins in tissue and mineral of the coralStylophora pistillata

“…The first published proteome analysis of the SOM in a stony coral (27) revealed a group of coral acid-rich proteins (CARPs) that can spontaneously catalyze the precipitation of calcium carbonate in vitro (28). The proteome also contained an assemblage of adhesion and structural proteins, which potentially create a framework for the precipitation of aragonite (27).…”