Abstract
For understanding the structural characteristics and the proteome of Perna shell, the microstructure, polymorph, and protein composition of the adult Perna viridis shell were investigated. The P. viridis shell have two distinct mineral layers, myostracum and nacre, with the same calcium carbonate polymorph of aragonite, determined by scanning electron microscope, Fourier transform infrared spectroscopy, and x-ray crystalline diffraction. Using Illumina sequencing, the mantle transcriptome of P. viridis was investigated and a total of 69,859 unigenes was generated. Using a combined proteomic/transcriptomic approach, a total of 378 shell proteins from P. viridis shell were identified, in which, 132 shell proteins identified with more than two matched unique peptides. Of the 132 shell proteins, 69 are exclusive to the nacre, 12 to the myostracum, and 51 are shared by both. The Myosin-tail domain containing proteins, Filament-like proteins, and Chitin-binding domain containing proteins represent the most abundant molecules. In addition, the shell matrix proteins (SMPs) containing biomineralization-related domains, such as Kunitz, A2M, WAP, EF-hand, PDZ, VWA, Collagen domain, and low complexity regions with abundant certain amino acids, were also identified from P. viridis shell. Collagenase and chitinase degradation can significantly change the morphology of the shell, indicating the important roles of collagen and chitin in the shell formation and the muscle-shell attachment. Our results present for the first time the proteome of P. viridis shell and increase the knowledge of SMPs in this genus.
Highlights
The bivalve shell, consisting of calcium carbonate crystals within an organic matrix, has been investigated as a typical biomineralization model for many years [1,2,3,4]
At the outside of the shell, we found that the tablets of the nacre layer become thicker and a prismatic-like layer can be seen at the outermost layer of the shell (Fig 1E and 1F)
Perna viridis shell proteome characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD)
Summary
The bivalve shell, consisting of calcium carbonate crystals within an organic matrix, has been investigated as a typical biomineralization model for many years [1,2,3,4]. The bivalve shell presents superior mechanical properties, such as stiffness, fracture toughness, and tensile strength, because of the complex architecture and involvement of biological macromolecules [5,6,7]. It is well known that there are three major polymorphs of calcium carbonate: calcite, aragonite, and vaterite. The two most thermodynamically stable structures, calcite and aragonite, are deposited extensively as biominerals [8]. Most adult bivalve shells are composed of calcite and/or aragonite and consist of various microstructures (or layers) with different.
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