Microstructure and in-depth proteomic analysis of Perna viridis shell

Ecotoxicological impact of heavy metals on wild mud crabs (Scylla olivacea) in Malaysia: An integrative approach of omics, molecular docking and human risk assessment

Mud crab, one of the aquatic organisms found in estuary areas, has become a significant economic source of seafood for communities due to its delectable taste. However, they face the threat of heavy metal contamination, which may adversely affect their biological traits. This study explored the comparison of the mud crabs collected from Setiu Wetland as a reference site, while Kuala Sepetang is an area that contains a higher concentration of heavy metals than Setiu Wetlands. Heavy metal levels were quantified using inductively coupled plasma mass spectrometry (ICP-MS), while proteomes were assessed using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and 1H nuclear magnetic resonance (NMR)-based metabolomics, respectively. Heavy metal contamination affects the proteome, metabolome, and putative molecular targets in mud crabs (Scylla olivacea), leading to oxidative stress. Mud crabs collected from the metal-polluted area of Kuala Sepetang in Perak had considerably elevated concentrations of nickel (Ni), copper (Cu), zinc (Zn), lead (Pb), chromium (Cr), and cadmium (Cd) in comparison to the reference site of Setiu Wetlands in Terengganu. The proteome analysis revealed an upregulation of the stress-response protein Hsp70, which triggered superoxide dismutase (SOD) and increased arginine kinase expression (5.47 fold) in the muscle tissue, results in the alteration of metabolite regulation in the mud crab from Kuala Sepetang. Additionally, in the muscle tissues of mud crabs obtained from Kuala Sepetang, uncharacterized myosin-tail 1 domain proteins and sarcoplasmic calcium-binding proteins were downregulated. The metabolomic investigation identified changes in metabolites associated with energy metabolism and osmoregulation. Exploration of docking analysis suggests potential connections between methylarsonic acid and essential proteins in mud crabs. These findings suggest that the presence of heavy metals disrupts physiological processes and highlights potential molecular targets that warrant further investigation.

Diversification of von Willebrand Factor A and Chitin-Binding Domains in Pif/BMSPs Among Mollusks

Pif is a shell matrix protein (SMP) identified in the nacreous layer of Pinctada fucata (Pfu) comprised two proteins, Pif97 and Pif 80. Pif97 contains a von Willebrand factor A (VWA) and chitin-binding domains, whereas Pif80 can bind calcium carbonate crystals. The VWA domain is conserved in the SMPs of various mollusk species; however, their phylogenetic relationship remains obscure. Furthermore, although the VWA domain participates in protein-protein interactions, its role in shell formation has not been established. Accordingly, in the current study, we investigate the phylogenetic relationship between PfuPif and other VWA domain-containing proteins in major mollusk species. The shell-related proteins containing VWA domains formed a large clade (the Pif/BMSP family) and were classified into eight subfamilies with unique sequential features, expression patterns, and taxa diversity. Furthermore, a pull-down assay using recombinant proteins containing the VWA domain of PfuPif 97 revealed that the VWA domain interacts with five nacreous layer-related SMPs of P. fucata, including Pif 80 and nacrein. Collectively, these results suggest that the VWA domain is important in the formation of organic complexes and participates in shell mineralisation.

Biomineralization in a cold environment: Insights from shield compositions and transcriptomics of polar sternaspids (Sternaspidae, Polychaeta)

The survival and physiological functions of polar marine organisms are impacted by global climate changes. Investigation of the adaptation mechanisms underlying biomineralization in polar organisms at low temperatures is important for understanding mineralized organismal sensitivity to climate change. Here, we performed electron probe analysis on the shields of Antarctic polychaete Sternaspis sendalli and Arctic polychaete Sternaspis buzhinskajae (Sternaspidae), and sequenced the transcriptomes of the tissues surrounding shields to examine biomineral characteristics and adaptive mechanisms in persistently cold environments. Compared to the temperate relative species, the relative abundance of iron, phosphorus, calcium, magnesium, nitrogen, sulfur and silicon in two polar sternaspid shields was similar to Sternaspis chinensis. However, the diversity and expression levels of biomineralization-related shell matrix proteins differed between the polar and temperate species, suggesting distinct molecular mechanisms underlying shield formation in cold environments. Tubulin and cyclophilin were upregulated compared to the temperate species. Furthermore, 42 positively selected genes were identified in Antarctic S. sendalli, with functions in cytoskeletal structure, DNA repair, immunity, transcription, translation, protein synthesis, and lipid metabolism. Highly expressed genes in both polar species were associated with cytoskeleton, macromolecular complexes and cellular component biosynthesis. Overall, this study reveals conserved elemental composition yet distinct biomineralization processes in the shields of polar sternaspids. The unique expression of biomineralization related genes and other cold-adaptation related genes provide molecular insights into biomineralization in cold marine environments.

Outer fold is sole effective tissue among three mantle folds with regard to oyster shell colour

Molluscs constitute the second largest phylum of animals in the world, and shell colour is one of their most important phenotypic characteristics. In this study, we found among three folds on the mantle edge of oyster, only the outer fold had the same colour as the shell. Transcriptome and mantle cutting experiment indicated that the outer fold may be mainly reflected in chitin framework formation and biomineralisation. There were obvious differences in SEM structure and protein composition between the black and white shell periostraca. The black shell periostraca had more proteins related to melanin biosynthesis and chitin binding. Additionally, we identified an uncharacterized protein gene (named as CgCBP) ultra-highly expressed only in the black outer fold and confirmed its function of chitin-binding and CaCO₃ precipitation promoting. RNAi also indicated that CgCBP knockdown could change the structure of shell periostracum and reduce shell pigmentation. All these results suggest that the mantle outer fold plays multiple key roles in shell periostraca bioprocessing, and shell periostracum structure affected by chitin-binding protein is functionally correlated with shell pigmentation. The investigation of oyster shell periostracum structure and shell colour will provide a better understanding in pigmentation during biological mineralisation in molluscs.

Structure and function of the periostracum in the bivalve Perna viridis

The periostracum is an outermost coating of all shelled-molluscs such as bivalves, corresponding to the interfacial layer separating the calcareous shells from the environment. It therefore plays a key role in the growth and survival of bivalves. Nevertheless, the periostracum has attracted little attention. Here, using the optical microscope (OM) and field-emission scanning electron microscope (FE-SEM), we investigate the structure and variation of the periostracum in the green mussel Perna viridis. We find that this periostracum has a novel sandwich structure with an outer (ODL) and inner dense layer (IDL) interleaved with a middle fibrous layer (MFL). The latter consists of locally parallel fibers (57-112 nm wide) and exhibits rich iridescent colors with a reversible hydrochromic behavior. Moreover, we find that this periostracum shows a significant variation in individual shells. Impressively, its thickness varies continuously along the shell edge. In addition, the periostracum at the ventral region is not only the thickest in a shell but also reinforced with the inorganic phosphate. We assume that this unusual variation in a same shell probably originates form defensive adaptations to predation and abrasion. Although many questions remain unanswered, this work reveals a new structure model of the periostracum, which not only advances our understanding of the periostracal formation mechanism, but also provides a natural prototype for design and synthesis of biomimetic coating and photonic materials.

Evolution of nacre- and prisms-related shell matrix proteins in the pen shell, Atrina pectinata

The molluscan shell is a good model for understanding the mechanisms underlying biomineralization. It is composed of calcium carbonate crystals and many types of organic molecules, such as the matrix proteins, polysaccharides, and lipids. The pen shell Atrina pectinata (Pterioida, Pinnidae) has two shell microstructures: an outer prismatic layer and an inner nacreous layer. Similar microstructures are well known in pearl oysters (Pteriidae), such as Pinctada fucata, and many kinds of shell matrix proteins (SMPs) have been identified from their shells. However, the members of SMPs that consist of the nacreous and prismatic layers of Pinnidae bivalves remain unclear. In this study, we identified 114 SMPs in the nacreous and prismatic layers of A. pectinata, of which only seven were found in both microstructures. 54 of them were found to bind calcium carbonate. Comparative analysis of nine molluscan shell proteomes showed that 69 of 114 SMPs of A. pectinata were found to have sequential similarity with at least one or more SMPs of other molluscan species. For instance, nacrein, tyrosinase, Pif/BMSP-like, chitinase (CN), chitin-binding proteins, CD109, and Kunitz-type serine proteinase inhibitors are widely shared among bivalves and gastropods. Our results provide new insights for understanding the complex evolution of SMPs related to nacreous and prismatic layer formation in the pteriomorph bivalves.

The first high-density genetic map of common cockle (Cerastoderma edule) reveals a major QTL controlling shell color variation

Shell color shows broad variation within mollusc species and despite information on the genetic pathways involved in shell construction and color has recently increased, more studies are needed to understand its genetic architecture. The common cockle (Cerastoderma edule) is a valuable species from ecological and commercial perspectives which shows important variation in shell color across Northeast Atlantic. In this study, we constructed a high-density genetic map, as a tool for screening common cockle genome, which was applied to ascertain the genetic basis of color variation in the species. The consensus genetic map comprised 19 linkage groups (LGs) in accordance with the cockle karyotype (2n = 38) and spanned 1073 cM, including 730 markers per LG and an inter-marker distance of 0.13 cM. Five full-sib families showing segregation for several color-associated traits were used for a genome-wide association study and a major QTL on chromosome 13 associated to different color-traits was detected. Mining on this genomic region revealed several candidate genes related to shell construction and color. A genomic region previously reported associated with divergent selection in cockle distribution overlapped with this QTL suggesting its putative role on adaptation.

The Mantle Transcriptome of Chamelea gallina (Mollusca: Bivalvia) and Shell Biomineralization

Simple Summary

Chamelea gallina is a bivalve mollusc that represents one of the most important fishery resources in the Mediterranean basin. In this species, the thickness and sturdiness of the shell valves are two important characteristics as they are decisive for protection against predators and survival of specimens rejected in the sea because caught under commercial size. The aim of this work is to investigate the ability of this species to modulate the expression of genes encoding proteins involved in shell biomineralization process in response to abiotic and biotic factors. Our findings, obtained through a multidisciplinary approach, highlighted a different shell mineralization behaviour in C. gallina clams collected in sampling sites characterized by different salinity and food availability. Moreover, this study provided the first comprehensive transcriptome from mantle, the tissue responsible for shell formation. Therefore, these results contribute to increase knowledge on this process and might help in adopting ad hoc management plans for this fishery resource.

Abstract

The striped venus Chamelea gallina is a bivalve mollusc that represents one of the most important fishery resources of the Adriatic Sea. In this work, we investigated for the first time the ability of this species to modulate the expression of genes encoding proteins involved in biomineralization process in response to biotic and abiotic factors. We provided the first comprehensive transcriptome from the mantle tissue of clams collected in two sampling sites located along the Italian Adriatic coast and characterized by different environmental features. Moreover, the assessment of environmental parameters, scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements on valves were conducted to better contextualize RNA sequencing (RNA-Seq) data. Functional annotation of differentially expressed genes (DEGs) and SEM observations highlighted a different shell mineralization behaviour in C. gallina clams collected from two selected sites characterized by diverse environmental parameters.

Optimized Sensory Units Integrated in the Chiton Shell

The first step for animals to interact with external environment is to sense. Unlike vertebrate animals with flexibility, it is challenging for ancient animals that are less flexible especially for mollusca with heavy shells. Chiton, as an example, has eight overlapping shells covering almost the whole body, is known to incorporate sensory units called aesthetes inside the shell. We used micro-computed tomography combined with quantitative image analysis to reveal the optimized shell geometry to resist force and the aesthetes' global distribution at the whole animal levels to facilitate sense from diverse directions both in the seawater and air. Additionally, shell proteomics combined with transcriptome reveals shell matrix proteins responsible for shell construction and potentially sensory function, highlighting unique cadherin-related proteins among mollusca. Together, this multi-level evidence of sensory units in the chiton shell may shed light on the formation of chiton shells and inspire the design of hard armor with sensory function.

Contamination gradient affects differently carbonic anhydrase activity of mollusks depending on their feeding habits

Aquatic organisms that inhabit coastal areas are often exposed to several contaminants. It is known that the bioaccumulation of contaminants can be amplified according to the species feeding habits and contaminant properties. As a consequence, species can experience different effects to contaminant exposure even if they inhabit the same area. The present study aimed to investigate the activities of carbonic anhydrase (CA), Ca²⁺-ATPase, and Mg²⁺-ATPase in different tissues (soft tissue, mantle, and gill) of three mollusk species (Lottia subrugosa, Stramonita brasiliensis, and Crassostrea brasiliana) with different feeding habits (herbivore, carnivore, and filter-feeder, respectively) which were sampled within a known contamination gradient at Santos Estuarine System (Southeastern Brazil). From the three enzymes tested, only CA was affected by the presence of contaminants within the contamination gradient evaluated. In general, the CA activity from the three species were lower in contaminated sites when compared to the reference site. The contrasting CA activity response observed in S. brasiliensis compared to L. subrugosa and C. brasiliana could be related to the tissue-specificity of this enzyme activity and species feeding habits (filter-feeders can accumulate more contaminants than herbivores and even carnivores). Results indicated that C. brasiliana mantle is the most suitable tissue for the use of CA analysis as a biomarker.

Hydrophilic Shell Matrix Proteins of Nautilus pompilius and the Identification of a Core Set of Conchiferan Domains

Despite being a member of the shelled mollusks (Conchiferans), most members of extant cephalopods have lost their external biomineralized shells, except for the basally diverging Nautilids. Here, we report the result of our study to identify major Shell Matrix Proteins and their domains in the Nautilid Nautilus pompilius, in order to gain a general insight into the evolution of Conchiferan Shell Matrix Proteins. In order to do so, we performed a multiomics study on the shell of N. pompilius, by conducting transcriptomics of its mantle tissue and proteomics of its shell matrix. Analyses of obtained data identified 61 distinct shell-specific sequences. Of the successfully annotated 27 sequences, protein domains were predicted in 19. Comparative analysis of Nautilus sequences with four Conchiferans for which Shell Matrix Protein data were available (the pacific oyster, the pearl oyster, the limpet and the Euhadra snail) revealed that three proteins and six protein domains were conserved in all Conchiferans. Interestingly, when the terrestrial Euhadra snail was excluded, another five proteins and six protein domains were found to be shared among the four marine Conchiferans. Phylogenetic analyses indicated that most of these proteins and domains were probably present in the ancestral Conchiferan, but employed in shell formation later and independently in most clades. Even though further studies utilizing deeper sequencing techniques to obtain genome and full-length sequences, and functional analyses, must be carried out in the future, our results here provide important pieces of information for the elucidation of the evolution of Conchiferan shells at the molecular level.

Proteomics of Shell Matrix Proteins from the Cuttlefish Bone Reveals Unique Evolution for Cephalopod Biomineralization

In contrast to the external shells in bivalves and gastropods, most cephalopods are missing this external protection. The cuttlefish, belonging to class cephalopod, has an internal biomineralized structure made of mainly calcium carbonate for controlling buoyancy. However, the macromolecules, especially proteins that control cuttlebone mineral formation, are not sufficiently understood, limiting our understanding of the evolution of this internal shell. In this study, we extracted proteins from the cuttlebone of pharaoh cuttlefish Sepia pharaonis and performed liquid chromatography-tandem mass spectrometry to identify the shell matrix proteins (SMPs). In total, 41 SMPs were identified. Among them, hemocyanin, an oxygen-carrying protein, was the most abundant SMP. By comparison with SMPs of other marine biominerals, hemocyanin, apolipophorin, soul domain proteins, transferrin, FL-rich, and enolase were found to be unique to the cuttlebone. In contrast, typical SMPs of external shells such as carbonic anhydrase complement control protein, fibronectin type III, and G/A-rich proteins were lacking from the cuttlebone. Furthermore, the cluster analysis of biomineral SMPs suggests that the SMP repertoire of the cuttlebone does not resemble that of other species with external shells. Taken together, this study implies a potential relationship of the cuttlefish internal shell with other internal biominerals, which highlights a unique shell evolutionary pathway in invertebrates.

The 'Shellome' of the Crocus Clam Tridacna crocea Emphasizes Essential Components of Mollusk Shell Biomineralization

Molluscan shells are among the most fascinating research objects because of their diverse morphologies and textures. The formation of these delicate biomineralized structures is a matrix-mediated process. A question that arises is what are the essential components required to build these exoskeletons. In order to understand the molecular mechanisms of molluscan shell formation, it is crucial to identify organic macromolecules in different shells from diverse taxa. In the case of bivalves, however, taxon sampling in previous shell proteomics studies are focused predominantly on representatives of the class Pteriomorphia such as pearl oysters, edible oysters and mussels. In this study, we have characterized the shell organic matrix from the crocus clam, Tridacna crocea, (Heterodonta) using various biochemical techniques, including SDS-PAGE, FT-IR, monosaccharide analysis, and enzyme-linked lectin assay (ELLA). Furthermore, we have identified a number of shell matrix proteins (SMPs) using a comprehensive proteomics approach combined to RNA-seq. The biochemical studies confirmed the presence of proteins, polysaccharides, and sulfates in the T. crocea shell organic matrix. Proteomics analysis revealed that the majority of the T. crocea SMPs are novel and dissimilar to known SMPs identified from the other bivalve species. Meanwhile, the SMP repertoire of the crocus clam also includes proteins with conserved functional domains such as chitin-binding domain, VWA domain, and protease inhibitor domain. We also identified BMSP (Blue Mussel Shell Protein, originally reported from Mytilus), which is widely distributed among molluscan shell matrix proteins. Tridacna SMPs also include low-complexity regions (LCRs) that are absent in the other molluscan genomes, indicating that these genes may have evolved in specific lineage. These results highlight the diversity of the organic molecules – in particular proteins – that are essential for molluscan shell formation.

PU14, a Novel Matrix Protein, Participates in Pearl Oyster, Pinctada Fucata, Shell Formation

Biomineralization is a widespread biological process, involved in the formation of shells, teeth, and bones. Shell matrix proteins have been widely studied for their importance during shell formation. In 2015, our group identified 72 unique shell matrix proteins in Pinctada fucata, among which PU14 is a matrix protein detected in the soluble fraction that solely exists in the prismatic layer. However, the function of PU14 is still unclear. In this study, the full-length cDNA sequence of PU14 was obtained and functional analyses of PU14 protein during shell formation were performed. The deduced protein has a molecular mass of 77.8 kDa and an isoelectric point of 11.34. The primary protein structure contains Gln-rich and random repeat units, which are typical characteristics of matrix protein and indicate its potential function during shell formation. In vivo and in vitro experiments indicated PU14 has prismatic layer functions during shell formation. The tissue expression patterns showed that PU14 was mainly expressed in the mantle tissue, which is consistent with prismatic layer formation. Notching experiments suggested that PU14 responded to repair and regenerate the injured shell. After inhibiting gene expression by injecting PU14-specific double-stranded RNA, the inner surface of the prismatic layer changed significantly and became rougher. Further, in vitro experiments showed that recombinant protein rPU14 impacted calcite crystal morphology. Taken together, characterization and functional analyses of a novel matrix protein, PU14, provide new insights about basic matrix proteins and their functions during shell formation.

Diversified Biomineralization Roles of Pteria penguin Pearl Shell Lectins as Matrix Proteins

Previously, we isolated jacalin-related lectins termed PPL2, PPL3 (PPL3A, 3B and 3C) and PPL4 from the mantle secretory fluid of Pteria penguin (Mabe) pearl shell. They showed the sequence homology with the plant lectin family, jacalin-related β-prism fold lectins (JRLs). While PPL3s and PPL4 shared only 35%–50% homology to PPL2A, respectively, they exhibited unique carbohydrate binding properties based on the multiple glycan-binding profiling data sets from frontal affinity chromatography analysis. In this paper, we investigated biomineralization properties of these lectins and compared their biomineral functions. It was found that these lectins showed different effects on CaCO₃ crystalization, respectively, although PPL3 and PPL2A showed similar carbohydrate binding specificities. PPL3 suppressed the crystal growth of CaCO₃ calcite, while PPL2A increased the number of contact polycrystalline calcite composed of more than one crystal with various orientations. Furthermore, PPL4 alone showed no effect on CaCO₃ crystalization; however, PPL4 regulated the size of crystals collaborated with N-acetyl-D-glucosamine and chitin oligomer, which are specific in recognizing carbohydrates for PPL4. These observations highlight the unique functions and molecular evolution of this lectin family involved in the mollusk shell formation.

Pearl Sac Gene Expression Profiles Associated With Pearl Attributes in the Silver-Lip Pearl Oyster, Pinctada maxima

Pearls are highly prized biomineralized gemstones produced by molluscs. The appearance and mineralogy of cultured pearls can vary markedly, greatly affecting their commercial value. To begin to understand the role of pearl sacs—organs that form in host oysters from explanted mantle tissues that surround and synthesize pearls—we undertook transcriptomic analyses to identify genes that are differentially expressed in sacs producing pearls with different surface and structural characteristics. Our results indicate that gene expression profiles correlate with different pearl defects, suggesting that gene regulation in the pearl sac contributes to pearl appearance and quality. For instance, pearl sacs that produced pearls with surface non-lustrous calcification significantly down-regulate genes associated with cilia and microtubule function compared to pearl sacs giving rise to lustrous pearls. These results suggest that gene expression profiling can advance our understanding of processes that control biomineralization, which may be of direct value to the pearl industry, particularly in relation to defects that result in low value pearls.

Molecular Characterization of a Novel Shell Matrix Protein With PDZ Domain From Mytilus coruscus

Mollusk shells are products of biomineralization and possess excellent mechanical properties, and shell matrix proteins (SMPs) have important functions in shell formation. A novel SMP with a PDZ domain (PDZ-domain-containing-protein-1, PDCP-1) was identified from the shell matrices of Mytilus coruscus. In this study, the gene expression, function, and location of PDCP-1 were analyzed. PDCP-1 was characterized as an ∼70 kDa protein with a PDZ (postsynaptic density/discs large/zonula occludes) domain and a ZM (ZASP-like motif) domain. The PDCP-1 gene has a high expression level and specific location in the foot, mantle and adductor muscle. Recombinantly expressed PDCP-1 (rPDCP-1) altered the morphology of calcite crystals, the polymorph of calcite crystals, binding with both calcite and aragonite crystals, and inhibition of the crystallization rate of calcite crystals. In addition, anti-rPDCP-1 antibody was prepared, and immunohistochemistry and immunofluorescence analyses revealed the specific location of PDCP-1 in the mantle, the adductor muscle, and the aragonite (nacre and myostracum) layer of the shell, suggesting multiple functions of PDCP-1 in biomineralization, muscle-shell attachment, and muscle attraction. Furthermore, pull-down analysis revealed 19 protein partners of PDCP-1 from the shell matrices, which accordingly provided a possible interaction network of PDCP-1 in the shell. These results expand the understanding of the functions of PDZ-domain-containing proteins (PDCPs) in biomineralization and the supramolecular chemistry that contributes to shell formation.

Recombinant transgelin-like protein 1 from Mytilus shell induces formation of CaCO3 polymorphic crystals in vitro

Transgelin is an actin cross-linking/gelling protein of the calponin family, which is associated with actin stress fibres, cell motility, adhesion and the maintenance of cell morphology. Transgelin-like proteins (TLPs) have also been identified as shell matrix proteins (SMPs) in several mollusc species; however, the functions of TLPs in biomineralization remain unknown. Transgelin-like protein 1 (TLP-1) was previously identified from the shell of Mytilus coruscus as a novel 19 kDa SMP with a calponin homology (CH) domain. To understand the role of TLP-1 in shell formation, the expression level and localization of the TLP-1 gene in biomineralization-related tissues were determined in this study. Furthermore, recombinant TLP-1 was expressed in a prokaryotic expression system with codon optimization, and an anti-rTLP-1 antibody was prepared based on the expressed recombinant TLP-1 (rTLP-1) protein. In vitro, rTLP-1 induced the formation of CaCO3 polymorphic crystals with distinct morphologies and inhibited crystallization rate and crystal interactions. Immunohistochemical, immunofluorescence, and pull-down analyses using the anti-rTLP-1 antibody revealed the specific locations of TLP-1 in biomineralization-related tissues and shell myostracum layer, and suggested the existence of a possible TLP-1 interaction network in the shell matrix. Our results are beneficial for understanding the functions of TLP-1, particularly through its CH domain, during shell mineralization.

Molecular characterization of a whirlin-like protein with biomineralization-related functions from the shell of Mytilus coruscus

Mollusc shells are produced from calcified skeletons and have excellent mechanical properties. Shell matrix proteins (SMPs) have important functions in shell formation. A 16.6 kDa whirlin-like protein (WLP) with a PDZ domain was identified in the shell of Mytilus coruscus as a novel SMP. In this study, the expression, function, and location of WLP were analysed. The WLP gene was highly expressed and specifically located in the adductor muscle and mantle. The expression of recombinant WLP (rWLP) was associated with morphological change, polymorphic change, binding ability, and crystallization rate inhibition of the calcium carbonate crystals in vitro. In addition, an anti-rWLP antibody was prepared, and the results from immunohistochemistry and immunofluorescence analyses revealed the specific location of the WLP in the mantle, adductor muscle, and myostracum layer of the shell, suggesting multiple functions for WLP in biomineralization, muscle-shell attachment, and muscle attraction. Furthermore, results from a pull-down analysis revealed 10 protein partners of WLP in the shell matrices and a possible network of interacting WLPs in the shell. In addition, in this study, one of the WLP partners, actin, was confirmed to have the ability to bind WLP. These results expand the understanding of the functions of PDZ-domain-containing proteins in biomineralization and provide clues for determining the mechanisms of myostracum formation and muscle-shell attachment.

Ps19, a novel chitin binding protein from Pteria sterna capable to mineralize aragonite plates in vitro

Mollusk shell is composed of two CaCO3 polymorphs (calcite and aragonite) and an organic matrix that consists of acetic acid- or ethylenediaminetetraacetic acid (EDTA)-soluble and insoluble proteins and other biomolecules (polysaccharides, β-chitin). However, the shell matrix proteins involved in nacre formation are not fully known. Thus, the aim of this study was to identify and characterize a novel protein from the acetic acid-insoluble fraction from the shell of Pteria sterna, named in this study as Ps19, to have a better understanding of the biomineralization process. Ps19 biochemical characterization showed that it is a glycoprotein that exhibits calcium- and chitin-binding capabilities. Additionally, it is capable of inducing aragonite plate crystallization in vitro. Ps19 partial peptide sequence showed similarity with other known shell matrix proteins, but it displayed similarity with proteins from Crassostrea gigas, Mizuhopecten yessoensis, Biomphalaria glabrata, Alpysia californica, Lottia gigantea and Elysia chlorotica. The results obtained indicated that Ps19 might play an important role in nacre growth of mollusk shells.