Characterization and functional analysis of a novel mannose-binding lectin from the swimming crab Portunus trituberculatus

Characteristics and functional analysis of a novel mannose receptor in Penaeus vannamei

The mannose receptor (MR) plays a key role in the innate immune system as a pattern recognition receptor. Here, a novel type of mannose receptor, named PvMR2, was identified from Penaeus vannamei (P. vannamei). The PvMR2 coding sequence (CDS) obtained was 988 base pairs in length, encoding a protein consisting of 328 amino acids. This protein includes a signal peptide and two classical C-type lectin domains (CTLD). Quantitative real-time PCR showed that PvMR2 was distributed in all detected tissues, with the highest levels in the intestines and stomach. Following a bacterial challenge with Vibrio anguillarum (V. anguillarum), PvMR2 showed significant up-regulation in both the intestines and stomach of shrimp. To validate the function of PvMR2, recombinant proteins were extracted and purified using a His-tag. The resulting rPvMR2 demonstrated binding capability with lipopolysaccharides (LPS) and peptidoglycan (PGN) in a dose-dependent manner, affirming its binding affinity. The purified rPvMR2 demonstrated calcium-independent binding activity towards both Gram-positive bacteria (V. anguilliarum and Vibrio parahaemolyticus) and Gram-negative bacteria (Escherichia coli and Aeromonas Veronii). Antibacterial assays confirmed that rPvMR2 inhibits bacterial growth. Intestinal adhesion and adhesion inhibition experiments confirmed that the rPvMR2 can be used to reduce the adhesion capacity of harmful bacteria in the gut. Phagocytosis experiments have shown that rPvMR2 promotes phagocytosis in hemocytes and protects the host from external infection. Treatment with recombinant PvMR2 significantly bolstered bacterial clearance within the hemolymph and markedly augmented shrimp survival post-infection with V. anguillarum. These results suggest that PvMR2 has agglutination, growth inhibition, adhesion inhibition, clearance promotion, and phagocytosis effects on harmful bacteria, and plays a crucial role in the antimicrobial immune response of P. vannamei.

Crab microRNA-381-5p regulates prophenoloxidase activation and phagocytosis to promote intracellular bacteria Spiroplasma eriocheiris infection by targeting mannose-binding protein

Mannose-binding lectin plays an essential role in bacteria or virus-triggered immune response in mammals. Previous proteomic data revealed that in Eriocheir sinensis, the mannose-binding protein was differentially expressed after Spiroplasma eriocheiris infection. However, the function of mannose-binding protein against pathogen infection in invertebrates is poorly understood. In this study, a crab mannose-binding protein (EsMBP) was characterized and enhanced the host resistance to S. eriocheiris infection. The application of recombinant C-type carbohydrate recognition domain (CTLD) of EsMBP led to increased crab survival and decreased S. eriocheiris load in hemocytes. Meanwhile, the overexpression of CTLD of EsMBP in Raw264.7 cells inhibited S. eriocheiris intracellular replication. In contrast, depletion of EsMBP by RNA interference or antibody neutralization attenuated phenoloxidase activity and hemocyte phagocytosis, rendering host more susceptible to S. eriocheiris infection. Furthermore, miR-381-5p in hemocytes suppressed EsMBP expression and negatively regulated phenoloxidase activity to exacerbate S. eriocheiris invasion of hemocytes. Taken together, our findings revealed that crab mannose-binding protein was involved in host defense against S. eriocheiris infection and targeted by miR-381-5p, providing further insights into the control of S. eriocheiris spread in crabs.

Heat stress, especially when coupled with high light, accelerates the decline of tropical seagrass (Enhalus acoroides) meadows

Heat stress threatens the survival of seagrass, but its damage mechanisms are unclear. In this study, the results reveal that heat stress exceeding 36 °C in the dark caused inactivation of the PSII reaction center, damaging both the PSII donor and acceptor sides in Enhalus acoroides. High light further increased the damage to the photosynthetic apparatus under heat stress. The stronger the heat stress under high light, the harder the recovery of photosynthetic activity. Therefore, during ebb tide at noon in nature, heat stress combined with strong light would induce a significant, even irreversible decrease in photosynthetic activity. Moreover, the heat stress hindered the transcription of psbA and RuBisCO, enhanced respiratory O₂, and induced severe peroxidation even if the SOD, APX, and GPX activities significantly improved. The results clearly suggest that heat stress, especially when coupled with high light, may be an important cause for the decline of E. acoroides meadows.

Complement-related proteins in crustacean immunity

As an important part of innate immune system, complement system is widely involved in defense response and immune regulation, and plays an important biological role. The complement system has been deeply studied. More than 30 complement-related molecules and three major complement-activation pathways have been identified in vertebrates. Crustacean animals do not have complement system. There are only some complement-related proteins in crustaceans which are important for host defense. In this review, we summarize the current knowledge about complement-related proteins in crustaceans, and their functions in crustacean immunity. We also make a comparation of the crustacean pro-phenoloxidase activating system and the mammalian complement system. This review provides a better understanding of the evolution and function of complement-related proteins in crustaceans.

A pattern recognition receptor ficolin from Portunus trituberculatus (Ptficolin) regulating immune defense and hemolymph coagulation

Ficolins, belonging to the fibrinogen-related protein superfamily, are important pattern recognition receptors in innate immunity. Here, a ficolin gene Ptficolin was characterized from the swimming crab Portunus trituberculatus. The completed cDNA sequence of Ptficolin encoded a signal peptide, a coiled-coil region and a fibrinogen-like domain but without the typical collagen region of vertebrate ficolins. Ptficolin showed higher expression in stomach and hepatopancreas, and presented a time-dependent response after pathogen challenge and injury stimulation. The recombinant Ptficolin (rPtficolin) could bind to various PAMPs and microorganisms, and agglutinate microorganisms and rabbit erythrocytes in a Ca²⁺-dependent manner, with strong binding ability to N-acetyl sugars. Meanwhile, rPtficolin promoted the hemocyte phagocytosis and clearance activity of Vibrio, while Ptficolin knockdown impaired the bacterial phagocytosis and clearance ability, suggesting the opsonin activity of Ptficolin. Knockdown of Ptficolin could downregulate the transcription of most complement-like genes and AMPs, but enhance the expression of most proPO system-related genes and key genes of Toll, IMD and JNK pathways. Moreover, knockdown of Ptficolin led to the increased hemolymph clotting time and the decreased expression of clotting-related genes. Our results indicate that Ptficolin could recognize and eliminate invading pathogens, and might be a prominent component in hemolymph coagulation of crab.

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.

Effects of ammonia-N stress on molecular mechanisms associated with immune behavior changes in the haemocytes of Litopenaeus vannamei

High concentration of ammonia-N will inhibit the immune defense of aquatic animals. The neuroendocrine-immune (NEI) regulatory mechanism under ammonia-N stress has been systematically studied, but the final response mechanism of ammonia-N affecting the immune system remains unclear. To investigate the relationship among immune factors of Litopenaeus vannamei (L. vannamei) exposed to 0, 2, 10 and 20 mg/L ammonia-N, the determination of complement components, C-type lectins, proPO system, signal transduction pathway and phagocytosis as well as exocytosis were performed. The results showed that the expressions of complement components including C1q, MBL, ficolin and alpha-2 macroglobulin (A2M) and the complement receptor integrin were decreased significantly in ammonia-N treatment groups at 6,12 and 24 h. C-type lectins and signal transduction factors changed significantly. The decrease of phagocytosis-related genes and phagocytic activity were similar to the changes of complement components, C-type lectins and the signal pathway. The mRNA abundance of exocytosis-related genes was significantly down-regulated under ammonia-N exposure. Correspondingly, significantly changes occurred in the expressions of PPAE and PPO3, immune factors-related genes (Pen3, crustin, stylicins, ALFs and LYC) and inflammatory factors (HSP90, TNFα, IL-16) in haemocytes. Eventually, the serine proteinase activity, PO activity, antibacterial activity and bacteriolytic activity in plasma were decreased significantly. In addition, we speculated that under ammonia-N stress, phagocytosis and exocytosis were affected by complement components, and C-type lectins through intracellular signal transduction pathway. Complement components may involve in the regulation of proPO-activating system to response to ammonia-N stress. This study helped to further understanding the relationship among immune factors of crustacean in response to environmental stress, which implied that when it comes to the decrease of immunity affected by environmental stress, we should not only focus on the mechanism of upstream neuroendocrine response, but also pay attention to the role of immune factors.

Molecular Mechanisms Underlying Vibrio Tolerance in Ruditapes philippinarum Revealed by Comparative Transcriptome Profiling

The clam Ruditapes philippinarum is an important species in the marine aquaculture industry in China. However, in recent years, the aquaculture of R. philippinarum has been negatively impacted by various bacterial pathogens. In this study, the transcriptome libraries of R. philippinarum showing different levels of resistance to challenge with Vibrio anguillarum were constructed and RNA-seq was performed using the Illumina sequencing platform. Host immune factors were identified that responded to V. anguillarum infection, including C-type lectin domain, glutathione S-transferase 9, lysozyme, methyltransferase FkbM domain, heat shock 70 kDa protein, Ras-like GTP-binding protein RHO, C1q, F-box and BTB/POZ domain protein zf-C2H2. Ten genes were selected and verified by RT-qPCR, and nine of the gene expression results were consistent with those of RNA-seq. The lectin gene in the phagosome pathway was expressed at a significantly higher level after V. anguillarum infection, which might indicate the role of lectin in the immune response to V. anguillarum. Comparing the results from R. philippinarum resistant and nonresistant to V. anguillarum increases our understanding of the resistant genes and key pathways related to Vibrio challenge in this species. The results obtained here provide a reference for future immunological research focusing on the response of R. philippinarum to V. anguillarum infection.

Crucial roles of a novel exoskeletal-derived lectin in innate immunity of the oriental river prawn, Macrobrachium nipponense

As important pattern recognition receptors (PRRs), C-type lectins play crucial roles in the crustacean innate immune system. In this study, a novel C-type lectin, designated as MnLec1, was obtained from the exoskeleton of the oriental river prawn Macrobrachium nipponense for the first time. The full-length cDNA of MnLec1 was 1329 bp with an open reading frame of 774 bp. The predicted MnLec1 protein contains a single carbohydrate-recognition domain with an EPN/LND motif and one Ca²⁺ binding site-2. MnLec1 transcripts were widely detected in the tested tissues of M. nipponense and significantly up-regulated after Aeromonas hydrophila challenge. The recombinant MnLec1 protein was found to have a wide spectrum of binding activities towards various microorganisms, agglutinate two kinds of Gram-negative bacteria (Escherichia coli and A. hydrophila) in a Ca²⁺ -independent manner. What's more, the survivability of prawns was significantly down-regulated after RNAi of MnLec1 when infected with A. hydrophila. Collectively, these findings suggest that MnLec1 from the exoskeleton might function as a PRR and play a crucial role in immune defense against invading pathogens in M. nipponense.

A new calnexin modulates antibacterial immune response in obscure puffer Takifugu obscurus

Calnexin (Cnx) is a membrane-bound lectin chaperone of the endoplasmic reticulum. In this study, a novel Cnx homologue from the obscure puffer Takifugu obscurus was characterized, tentatively named ToCnx. The cDNA of ToCnx was 1803 bp, and it contained an open reading frame encoding a polypeptide of 600 amino acid residues with a calculated molecular weight of 67.5 kDa. Multiple alignment of the deduced amino acid sequences of ToCnx and other related fish Cnxs revealed that ToCnx had typical characteristics of fish Cnxs. Sequence comparison and phylogenetic tree analysis showed that ToCnx had the closest relationship with Cnxs from Takifugu flavidus and Takifugu rubripes. ToCnx transcripts were detected in all the tissues examined, and they were mainly expressed in the liver, kidney, and intestine. Upon Vibrio harveyi, Edwardsiella tarda, and Aeromonas hydrophila infection, ToCnx transcripts were all significantly upregulated in the kidneys. The recombinant calreticulin domain of ToCnx (rToCnx) was prepared by prokaryotic expression. In the absence of calcium, rToCnx was able to bind three Gram-negative bacteria (V. harveyi, E. tarda, and A. hydrophila) and two bacterial saccharides, such as lipopolysaccharide and peptidoglycan. In the presence of calcium, rToCnx could agglutinate all the detected microorganisms. In addition, rToCnx possessed the effect of inhibiting the growth of three microbe strains. These observations suggested that ToCnx is an important participant in host immune defense against bacteria.

Transcriptomic analysis using dual RNA sequencing revealed a Pathogen-Host interaction after Edwardsiella anguillarum infection in European eel (Anguilla anguilla)

Many studies have explored differentially expressed genes (DEGs) between some pathogens and hosts, but no study has focused on the interaction of DEGs between Edwardsiella anguillarum (Ea) and Anguilla anguilla (Aa). In this study, we examined the interactions of DEGs during Ea infection and Aa anti-infection processes by dual RNA sequencing. Total RNA from in vitro and in vivo (Aa liver) Ea culture was extracted. Using high-throughput transcriptomics, significant DEGs that were expressed between Ea cultured in vitro versus in vivo and those in the liver of the infected group versus control group were identified. Protein-protein interactions between the pathogen and host were explored using Cytoscape according to the HPIDB 3.0 interaction transcription database. The results showed that the liver in the infection group presented with severe bleeding and a large number of thrombi in the hepatic vessels. We found 490 upregulated and 398 downregulated DEGs of Ea in vivo versus Ea cultured in vitro, and 2177 upregulated and 970 downregulated genes in the liver of the infected eels. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of the pathogen DEGs revealed that the upregulated genes were mainly enriched in migration, colonization, biofilm formation, and significantly enriched in ABC transport and quorum sensing; the downregulated genes were mainly involved in metabolism, information transduction, organelle formation, enzyme catalysis, molecular transport, and binding. GO of the host DEGs showed that metabolic process, catalytic activity, single organism metabolic process, small molecule binding, nucleotide binding, nucleotide phosphate binding, and anion binding were markedly enriched. Finally, we found that 79 Ea and 148 Aa proteins encoded by these DEGs were involved in an interaction network, and some pathogen (DegP, gcvP, infC, carB, rpoC, trpD, sthA, and FhuB) and host proteins (MANBA, STAT1, ETS2, ZEP1, TKT1, NMI and RBPMS) appear to play crucial roles in infection. Thus, determining the interaction networks revealed crucial molecular mechanisms underlying the process of pathogenic infection and host anti-infection.

A C-Type Lectin Highly Expressed in Portunus trituberculatus Intestine Functions in AMP Regulation and Prophenoloxidase Activation

A C-type lectin (PtCLec2) from Portunus trituberculatus was identified for characterization of its role in defense and innate immunity. PtCLec2 contains a single carbohydrate-recognition domain (CRD) with a conserved QPD motif, which was predicted to have galactose specificity. The mRNA expression of PtCLec2 was predominantly detected in intestine and increased rapidly and significantly upon pathogen challenge. The recombinant PtCLec2 (rPtCLec2) could bind various microorganisms and PAMPs with weak binding ability to yeast and PGN. It agglutinated the tested Gram-negative bacteria (Vibrio alginolyticus and Pseudomonas aeruginosa), Gram-positive bacteria (Staphylococcus aureus and Micrococcus luteus), and rabbit erythrocytes in the presence of exogenous Ca²⁺, and these agglutination activities were suppressed by LPS, d-galactose, and d-mannose. Further, rPtCLec2 enhanced phagocytosis and clearance of V. alginolyticus, and displayed inhibitory activities against the tested bacteria. Knockdown of PtCLec2 decreased the transcription of two phagocytosis genes (PtArp and PtMyosin), three prophenoloxidase (proPO) system-related genes (PtPPAF, PtcSP1, and PtproPO), six antimicrobial peptides (AMPs) (PtALF4-7, PtCrustin1, and PtCrustin3), and PtRelish but upregulated the expression levels of PtJNK, PtPelle, and PtTLR. These results collectively indicate that PtCLec2 might perform its immune recognition function via binding and agglutination, and mediate pathogen elimination via regulating hemocyte phagocytosis, AMP synthesis, and proPO activation.

Characterization and functional analysis of fibrinogen-related protein (FreP) in the black tiger shrimp, Penaeus monodon

Ficolin is classified as an immune related protein containing collagen-like and fibrinogen-related domain (FreD). In invertebrates, the functions of fibrinogen-related proteins (FrePs) are of importance to innate immunity. In this study, a FreP in the black tiger shrimp Penaeus monodon was identified and characterized. The PmFreP cDNA is 1,007 bp long with a 921 bp-open reading frame that encodes for 306 amino acids. The deduced PmFreP sequence consists of a signal peptide, an unknown region and the FreD. Phylogenetic analysis showed that PmFreP was clustered with fibrinogen-like proteins in crustaceans which was separated from vertebrate ficolin-like proteins. The deduced fibrinogen-like domain contains four conserved cysteine residues (Cys96, Cys127, Cys249, and Cys262) that are responsible for the formation of disulfide bridges. Gene expression analysis shows that Pmfrep is mainly expressed in the intestine and the expression is significantly upregulated after Vibrio harveyi and white spot syndrome virus (WSSV) challenge. Recombinant PmFreP (rPmFreP) were successfully expressed and purified, and forms a trimeric structure as judged by native-PAGE. Bacterial binding assay showed that the rPmFreD can bind and agglutinate Gram-negative and Gram-positive bacteria in the presence of calcium (Ca²⁺) ions. Moreover, the rPmFreP facilitates the clearance of V. harveyi in vivo. Overall, our results suggested that the PmFreP may serve as pattern recognition receptors implicated in shrimp innate immunity.

A stomach-specific lectin plays a crucial role in the innate immunity of red swamp crayfish, Procambarus clarkii

C-type lectins (CTLs) play important roles in innate immune system of crustaceans as pattern recognition receptors (PRRs). In this study, a novel CTL gene was obtained from the red swamp crayfish, Procambarus clarkii, designated as PcLec. PcLec encodes a peptide with 175 amino acids, with a signal peptide and a single carbohydrate recognition domain (CRD). The PcLec transcripts were specifically expressed in crayfish stomach and were induced by bacterial challenge. In vitro assays with recombinant PcLec protein revealed that it had bacterial binding activity, polysaccharide binding activity, bacterial agglutination activity, and antimicrobial activity. Most importantly, PcLec knockdown significantly impaired the survivability of crayfish upon oral infection with its pathogen A. hydrophila. According to these results, we infer that the PcLec plays a crucial role in antibacterial defense of crayfish.

TMT-based quantitative proteomic analysis of Eriocheir sinensis hemocytes and thoracic ganglion during Spiroplasma eriocheiris infection

Spiroplasma eriocheiris, a novel pathogen of Chinese mitten crab Eriocheir sinensis tremor disease, has led into catastrophic economic losses in aquaculture. S. eriocheiris invaded the hemocytes in the early stage, then invaded nerve tissue and caused typically paroxysmal tremors of pereiopod in the late stage of infection. The purpose of this study was to detect the infection mechanism of hemocytes in the early stage and thoracic ganglion in the late stage of S. eriocheiris infection at the protein level. Hemocytes and thoracic ganglion were collected at 24 h and 10 d after injection (the crabs with typical paroxysmal tremors of the pereiopod), respectively. TMT was performed with isobaric markers, followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). In hemocytes, 127 proteins were up-regulated and 85 proteins were down-regulated in 2747 quantified proteins. Many proteins and process including proPO system proteins, hemolymph coagulation system proteins and lectins were differently expressed in hemocytes and involved in the early immune process of E. sinensis against S. eriocheiris infection. Meanwhile, 545 significantly different expression proteins (292 down-regulated and 253 up-regulated protein including a number of immune-associated, nervous system development and signal transmission related proteins) were identified in thoracic ganglion in the late stage of S. eriocheiris infection. The qRT-PCR analysis results shown that the selected significantly changed proteins in hemocytes and thoracic ganglion were consistent with the TMT proteomics. This paper reported for the first time to study the responses of crab hemocyte and thoracic ganglion against the S. eriocheiris infection at different stages. These findings help us understand the infection mechanism of S. eriocheiris at different stage with the different tissue.

Microwave Hydrodiffusion and Gravity (MHG) Extraction from Different Raw Materials with Cosmetic Applications

Microwave hydrodiffusion and gravity (MHG) and ethanolic solid-liquid extraction were compared using selected plant sources. Their bioactive profile, color features, and proximate chemical characterization were determined. MHG extracts, commercial antioxidants, and three distinct types of thermal spring water were used in a sunscreen cream formulation. Their bioactive capacity, chemical and rheological properties were evaluated. MHG Cytisus scoparius flower extract provided the highest bioactive properties. Pleurotus ostreatus MHG liquor exhibited the highest total solid extraction yield. The Brassica rapa MHG sample stood out for its total protein content and its monosaccharide and oligosaccharide concentration. Quercus robur acorns divided into quarters supplied MHG extract with the lowest energy requirements, highest DPPH inhibition percentage, total lipid content and the highest enzyme inhibition. The chemical and bioactive capacities stability of the sunscreen creams elaborated with the selected MHG extracts and the thermal spring waters showed a similar behavior than the samples containing commercial antioxidants.