Separation, identification and gene expression analysis of PmAMP-1 from Pinctada fucata martensii

Identification and functional characterization of a superoxide dismutase (CuZnSOD) from Pinctada fucata martensii

Copper/zinc superoxide dismutase (Cu/Zn-SOD) can effectively eliminate reactive oxygen species (ROS)，avoid damage from O2 to the body, and maintain O2 balance. In this study, multi-step high-performance liquid chromatography (HPLC), combined with Mass Spectrometry (MS), was used to isolate and identify Cu/Zn-SOD from the serum of Pinctada fucata martensii (P. f. martensii) and was designated as PmECSOD. With a length of 1864 bp and an open reading frame (ORF) of 1422 bp, the cDNA encodes a 473 amino acid protein. The PmECSOD transcript was detected in multiple tissues by quantitative real-time PCR (qRT-PCR), with its highest expression level being in the gills. Additionally, the temporal expression of PmECSOD mRNA in the hemolymph was highest at 48 h after in vivo stimulation with Escherichia coli and Micrococcus luteus. The results from this study provide a valuable base for further exploration of molluscan innate immunity and immune response.

Molecular cloning, expression, and functional analysis of a putative lectin from the pearl oyster (Pinctada fucata, Gould 1850)

Marine lectins are a group of proteins that possess specific carbohydrate recognition and binding domains. They exhibit various activities, including antimicrobial, antitumor, antiviral, and immunomodulatory effects. In this study, a novel galectin-binding lectin gene named PFL-96 (GenBank: OQ561753.1) was cloned from Pinctada fucata. The PFL-96 gene has an open reading frame of 324 base pairs (bp) and encodes a protein comprising 107 amino acids. The protein has a molecular weight of 11.95 kDa and an isoelectric point of 9.27. It contains an N-terminal signal peptide and a galactose-binding lectin domain. The sequence identity to lectin proteins from fish, echinoderms, coelenterates, and shellfish ranges from 31.90 to 40.00 %. In the phylogenetic analysis, it was found that the PFL-96 protein is closely related to the lectin from Pteria penguin. The PFL-96 recombinant protein exhibited coagulation activity on 2 % rabbit red blood cells at a concentration of ≥8 μg/mL. Additionally, it showed significant hemolytic activity at a concentration of ≥32 μg/mL. The PFL-96 recombinant protein exhibited significant antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Candida albicans, and Vibrio alginolyticus, with minimum inhibitory concentrations (MIC) of 4, 8, 16, and 16 μg/mL, respectively. The minimum bactericidal concentrations (MBC) were determined to be 8, 16, 32, and 32 μg/mL, respectively. Furthermore, the PFL-96 recombinant protein exhibited inhibitory effects on the proliferation of Hela tumor cells, HepG2 tumor cells, and C666-1 tumor cells, with IC50 values of 7.962, 8.007, and 9.502 μg/mL, respectively. These findings suggest that the recombinant protein PFL-96 exhibits significant bioactivity in vitro, contributing to a better understanding of the active compounds found in P. fucata. The present study establishes a fundamental basis for further investigation into the mechanism of action and structural optimization of the recombinant protein PFL-96. The aim is to develop potential candidates for antibacterial and anti-tumor agents.

Preliminary investigation of the immune activity of PmH2A-derived antimicrobial peptides from the pearl oyster Pinctada fucata martensii

Antimicrobial peptides (AMPs) play important roles in the immune defense against pathogenic microorganisms. For instance, histone 2A (H2A)-derived AMPs is an antimicrobial peptide involved in the host's innate immune defense and immunoregulation. AMPs have been isolated from the pearl oyster Pinctada fucata martensii but their role in host defense remains poorly understood. To elucidate the structural features of P. f. martensii H2A (PmH2A)-derived AMPs and their potential immune functions, we synthesized a series of laboratory-designed synthetic analogs of PmH2A and examined their antimicrobial properties, as well as their mechanisms of action. This analysis revealed inhibitory effects on the growth of Gram-positive and Gram-negative bacteria. Further assessment by transmission electron microscopy (TEM) of two of the three peptides, PmH2A-AMP and PmH2A-AMP(5-13)[KLLK]₃, confirmed that it exerted an anti-bacterial activity through membrane lysis. Finally, we found that the hemocytes and gills of P. f. martensii released antimicrobial H2A histones in response to LPS exposure, mimicking tissue damage and infection. This immune response is reminiscent of the neutrophil extracellular traps (NETs) recently described in oysters. Thus, the LPS challenge is sufficient to induce histone-derived peptide accumulation in pearl oyster P.f. martensii.

Members of the histone-derived antimicrobial peptide family from the pearl oyster Pinctada fucata martensii: Inhibition of bacterial growth

Because it is difficult to isolate standard antimicrobial peptides (AMPs) using traditional biochemical approaches, we designed, synthesized, and evaluated a series of structurally altered histone-derived AMPs (HDAPs) from the pearl oyster Pinctada fucata martensii using molecular cloning approaches. Four histone-homolog genes (PmH2A, PmH2B, PmH3, and PmH4-1) were identified, of which PmH2A and PmH2B had yet to be described. PmH2A and PmH2B were therefore cloned using Rapid Amplification of cDNA Ends (RACE) and characterized. Constitutive PmH2A and PmH2B mRNA expression was detected in all six pearl oyster tissues tested, with comparatively greater transcript abundance in the gonads. Because α-helical content, hydrophilicity index, and the presence of a proline hinge may be the three important factors influencing the antimicrobial efficacy of HDAPs, we synthesized a series of eight N- and C-terminally truncated or amino acid-substituted synthetic candidate HDAP analogs derived from PmH2A, PmH2B, PmH3, and PmH4-1. Only the PmH2A- and PmH4-derived AMPs inhibited bacterial growth. The PmH2A-derived AMPs were α-helical proteins, while the PmH4-derived AMPs were extended strand/random coil proteins. Our results suggested that having an α-helical structure was particularly important for the antibacterial efficacy of the PmH2A-derived peptides; amphipathic structures (hydrophilic index, 0.3 to -0.3) may enhance the antimicrobial function of both the PmH2A- and PmH4-derived peptides. The high antibacterial efficacy of one of the HDAP analogs studied, PmH2A-AMP (5-13) [KLLK]₃, indicated that this protein may represent a promising candidate for the treatment of bacterial infections in aquaculture mollusk species. This first study of HDAPs from the pearl oyster P. f. martensii provides new insights into the design and function of highly effective antimicrobial peptides.

Gene cloning and functional study of PmKSPI from Pinctada fucata martensii

Kunitz-type serine protease inhibitors (KSPI) are a family of serine protease inhibitors (SPIs) and are extensively found in animals, plants, and microbes. SPI can inhibit proteases that may be harmful or unwanted to its cells. Here, a four-domain Kunitz-type SPI, PmKSPI, was cloned by RACE in the pearl oyster Pinctada fucata martensii. The full-length cDNA sequence of PmKSPI was 1318 bp, including the 5' UTR (25 bp), the 3' UTR (96 bp) and ORF (1197 bp). Homology analysis indicated that PmKSPI had the highest resemblance (30.14%) with its homolog in Crassostrea gigas. Phylogenetic analysis revealed that PmKSPI clustered with homologs in other molluscs. We found that PmKSPI mRNA expression in P. f. martensii was distributed in all six tissues, with the highest level in the mantle, and almost no expression in other tissues. After PAMPs challenge, expression of PmKSPI mRNA in the mantle was significantly up-regulated. The recombinant protein rPmKSPI significantly inhibited the growth of 5 kinds of Gram-negative bacteria but had little effect on Gram-positive bacterial activity. Transmission electron microscopy showed that plasmolysis occurred in two Gram-negative bacteria species when treated with rPmKSPI. rPmKSPI may thus have a bactericidal effect by destroying the bacterial cell membrane or cell walls and releasing its contents. Therefore, our results suggest that PmKSPI is tightly associated with the immunological defence of P. f. martensii.

Comprehensive analysis of the lncRNAs, mRNAs, and miRNAs implicated in the immune response of Pinctada fucata martensii to Vibrio parahaemolyticus

Non-coding RNAs (ncRNAs) have been implicated in a variety of biological processes. However, most ncRNAs are of unknown function and are as-yet unannotated. The immune-related functions of ncRNAs in the pearl oyster Pinctada fucata martensii were explored based on transcriptomic differences in the expression levels of long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and messenger RNAs (mRNAs) in the hemocytes of P.f. martensii after challenge by the pathogenic bacterium Vibrio parahaemolyticus. Across the challenged and control pearl oysters, 144 miRNAs and 14,571 lncRNAs were identified. In total, 13,375 ncRNAs were differentially expressed between the challenged and control pearl oysters; in the challenged pearl oysters as compared to the controls, 15 miRNAs and 5147 lncRNAs were upregulated, while 51 miRNAs and 8162 lncRNAs were downregulated. The sequencing results were validated using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. GO and KEGG pathway analysis showed that genes targeted by the differentially expressed ncRNAs were associated with the vascular endothelial growth factor (VEGF) signaling pathway and the nuclear factor kappa-B (NF-κB) signaling pathway. An lncRNA-mRNA-miRNA network that was developed based on the transcriptomic results of this study suggested that lncRNAs may compete with miRNAs for mRNA binding sites. This study may provide a useful framework for the detection of additional novel ncRNAs, as well as new insights into the pathogenic mechanisms underlying the response of P.f. martensii to V. parahaemolyticus.

The succinylome of Pinctada fucata martensii implicates lysine succinylation in the allograft-induced stress response

Lysine succinylation is a novel protein post-translational modification associated with the regulation of a variety of cellular processes. Post-translational modifications may regulate the immune response of Pinctada fucata martensii, a marine bivalve used to produce cultured pearls, in response to the surgical implantation of the seed pearl. This allograft-induced stress response may lead to transplant rejection or host death. However, the regulatory effects of post-translational modifications following nucleus insertion surgery in P.f. martensii remain largely unknown. Here, we used 4D label-free quantitative proteomics (4D-LFQ) with LC-MS/MS to explore the effects of nucleus implantation on lysine succinylation in P.f. martensii. We identified 4430 succinylated sites on 964 succinylated proteins in P.f. martensii after nucleus insertion surgery, and seven conserved motifs were identified upstream and downstream of these sites. In total, 269 succinylation sites were differentially expressed in response to implantation (|fold-change| > 1.5 and FDR <1%; 211 upregulation and 58 downregulation), corresponding to 163 differentially expressed succinylated proteins (DESPs; 124 upregulated and 39 downregulated). The terms over-enriched in the DESPs included "cellular processes", "metabolic pathways", and "binding activity", while the significantly enriched pathways included "ECM-receptor interaction", "PI3K-Akt signaling", and "focal adhesion". "EGF-like structural domains", "platelet-responsive protein type 1 structural domains", and "laminin EGF-like (domains III and V) domains" were overrepresented in the DESPs. Parallel reaction-monitoring (PRM) analysis validated 13 DESPs from the proteomics data. The succinylome of P.f. martensii (generated here for the first time) helps to clarify the biological role of large-scale succinylation in this bivalve after nucleus insertion surgery, providing a theoretical basis for further investigations of stress-induced post-translational modifications in other mollusks and extending our knowledge of the molluscan succinylated proteome.

Cloning and functional analysis of a trypsin-like serine protease from Pinctada fucata martensii

Trypsin-like serine proteases (TLSs) play various roles in dietary protein digestion, hemolymph coagulation, antimicrobial peptide synthesis, and, in particular, the rapid immune pathways activated in response to pathogen detection. The cultured pearl industry, of which Pinctada fucata martensii is one of the most important species, is plagued by disease, thus leading to large economic losses. Herein, the molecular mechanisms underlying the innate immune response of P.f. martensii were explored. First, immune effector molecules from the P.f. martensii genome were screened and a TLS-like gene encoding a protein with a trypsin domain, herein designated as PmTLS, was identified. A multi-sequence alignment indicated a low sequence homology between PmTLS and other mollusk TLS-like proteins. Furthermore, a neighbor-joining phylogenetic analysis indicated that PmTLS has the closest genetic relationship to a Crassostrea gigas TLS. Additionally, real-time quantitative PCR (qPCR) analysis showed that PmTLS mRNA is constitutively expressed in all of the 6 examined P.f. martensii tissues, with significantly higher expression noted in hemocytes relative to the other tissues examined (p < 0.05). P.f. martensii samples were then challenged with various pathogen-associated molecular patterns (PAMPs), including lipopolysaccharide, peptidoglycan, and polyinosinic acid. In the challenge groups, PmTLS was significantly upregulated in hemocytes at 48 h post-challenge when compared to the unchallenged controls. Furthermore, treatment with recombinant PmTLS (rPmTLS) also significantly inhibited the growth of most of the examined gram-negative bacteria tested in vitro (p < 0.05), but it had little effect on the growth of the examined gram-positive bacteria. When examining morphological changes via transmission electron microscopy, rPmTLS treated bacteria exhibited morphological changes such as plasma wall separation. Thus, rPmTLS appears to play a bactericidal role by destroying bacterial cell membranes or cell walls, which subsequently leads to a release of the cellular contents and cell death. The findings presented herein have enabled further characterization of the immune defense mechanisms in P.f. martensii and may lead to improved disease control methods for the pearl cultivation industry.

Antimicrobial properties and immune-related gene expression of a C-type lectin isolated from Pinctada fucata martensii

C-type lectins are carbohydrate-binding proteins that play important roles in the innate immune response to pathogen infections. Here, multi-step high performance liquid chromatography (HPLC), combined with mass spectrometry (MS), was used to isolate and identify proteins with antibacterial activity from the serum of Pinctada fucata martensii. Using this method, we obtained a novel isoform of C-type lectin (PmCTL-1). PmCTL-1 strongly inhibited gram-positive bacteria. The complete cDNA sequence of PmCTL-1 was 636 bp in length, and encoded a protein 149 amino acids long, containing a typical carbohydrate recognition domain (CRD). A phylogenetic analysis based on a multiple sequence alignment indicated that PmCTL-1 was highly similar to C-type lectins from other mollusks. Fluorescent quantitative real-time PCR analysis showed that PmCTL-1 mRNA was strongly upregulated in the mantle of healthy P.f. martensii, but was expressed only at low levels in the gill, gonad, hepatopancreas, adductor muscle, and hemocytes. PmCTL-1 expression levels in the mantle and hemocytes increased significantly in response to bacterial stimulation. This study provides a valuable framework for further explorations of innate immunity and the immune response in mollusks.

In-Depth In Silico Search for Cuttlefish (Sepia officinalis) Antimicrobial Peptides Following Bacterial Challenge of Haemocytes

Cuttlefish (Sepia officinalis) haemocytes are potential sources of antimicrobial peptides (AMPs). To study the immune response to Vibrio splendidus and identify new AMPs, an original approach was developed based on a differential transcriptomic study and an in-depth in silico analysis using multiple tools. Two de novo transcriptomes were retrieved from cuttlefish haemocytes following challenge by V. splendidus or not. A first analysis of the annotated transcripts revealed the presence of Toll/NF-κB pathway members, including newly identified factors such as So-TLR-h, So-IKK-h and So-Rel/NF-κB-h. Out of the eight Toll/NF-κB pathway members, seven were found up-regulated following V. splendidus challenge. Besides, immune factors involved in the immune response were also identified and up-regulated. However, no AMP was identified based on annotation or conserved pattern searches. We therefore performed an in-depth in silico analysis of unannotated transcripts based on differential expression and sequence characteristics, using several tools available like PepTraq, a homemade software program. Finally, five AMP candidates were synthesized. Among them, NF19, AV19 and GK28 displayed antibacterial activity against Gram-negative bacteria. Each peptide had a different spectrum of activity, notably against Vibrio species. GK28—the most active peptide—was not haemolytic, whereas NF19 and AV19 were haemolytic at concentrations between 50 and 100 µM, 5 to 10 times higher than their minimum inhibitory concentration.

Collective Locomotion of Human Cells, Wound Healing and Their Control by Extracts and Isolated Compounds from Marine Invertebrates

The collective migration of cells is a complex integrated process that represents a common theme joining morphogenesis, tissue regeneration, and tumor biology. It is known that a remarkable amount of secondary metabolites produced by aquatic invertebrates displays active pharmacological properties against a variety of diseases. The aim of this review is to pick up selected studies that report the extraction and identification of crude extracts or isolated compounds that exert a modulatory effect on collective cell locomotion and/or skin tissue reconstitution and recapitulate the molecular, biochemical, and/or physiological aspects, where available, which are associated to the substances under examination, grouping the producing species according to their taxonomic hierarchy. Taken all of the collected data into account, marine invertebrates emerge as a still poorly-exploited valuable resource of natural products that may significantly improve the process of skin regeneration and restrain tumor cell migration, as documented by in vitro and in vivo studies. Therefore, the identification of the most promising invertebrate-derived extracts/molecules for the utilization as new targets for biomedical translation merits further and more detailed investigations.