Characterization and functional analysis of serine proteinase and serine proteinase homologue from the swimming crab Portunus trituberculatus

Identification and functional characterization of C-type lectins and crustins provide new insights into the immune response of Portunus trituberculatus

A meticulous understanding of the immune characteristics of aquaculture animals is the basis for developing precise disease prevention and control strategies. In this study, four novel C-type lectins (PtCTL-5, PtCTL-6, PtCTL-7 and PtCTL-8) including a single carbohydrate-recognition domain (CRD), and four novel crustins (Ptcrustin-1, Ptcrustin-2, Ptcrustin-3 and Ptcrustin-4) with a single whey acidic protein (WAP) domain were identified from the swimming crab Portunus trituberculatus. Tissue distribution analysis indicated that most of the target genes were predominantly expressed in the hepatopancreas in all examined tissues, except for Ptcrustin-1 which were mainly expressed in the gills. Our results showed that the eight genes displayed various transcriptional profiles across different tissues. In hemocytes, the PtCTL-7 responded quickly to Vibrio alginolyticus and exhibited much more strongly up-regulation than other three PtCTLs. The Ptcrustin-1 rapidly responded to V. alginolyticus within 3 h in all the three tested tissues. Furthermore, recombinant proteins of PtCTL-5 and PtCTL-8 were successfully obtained, and both of them displayed bacterial binding activities toward V. alginolyticus, V. harveyi and Staphylococcus aureus, and only showed antibacterial activity against V. harveyi. These findings provided new insights into the diverse immune response of P. trituberculatus and laid theoretical foundations for the development of precise disease prevention and control strategies in P. trituberculatus farming. Moreover, the specific anti-V. harveyi activities exhibited by rPtCTL-5 and rPtCTL-8 suggested their promising application prospects for controlling diseases caused by V. harveyi.

Characterization and functional analysis of a clip domain serine protease (MncSP) and its alternative transcript (MncSP-isoform) from Macrobrachium nipponense

Clip domain serine protease (cSPs) play an important role in the innate immune defense of crustaceans. In this study, a clip domain serine protease (MncSP) and its alternative transcript (MncSP-isoform) were identified from Macrobrachium nipponense. The full-length cDNA sequences of MncSP and MncSP-isoform were 2447 and 2351 bp with open reading frames comprising 1497 and 1401 bp nucleotides and encoding 498 and 466 amino acids, respectively. The genome of MncSP had 10 exons and 9 introns. MncSP contained all 10 exons, whereas MncSP-isoform lacked the second exon. MncSP and MncSP-isoform contained a signal peptide, a clip domain, and a Tryp_SPc domain. Phylogenetic tree analysis showed that MncSP and MncSP-isoform clustered with cSPs from Palaemonidae. MncSP and MncSP-isoform were widely distributed in hemocytes, heart, hepatopancreas, gills, stomach, and intestine. The expression profiles of MncSP and MncSP-isoform in the hemocytes of M. nipponense changed after simulation by Vibrio parahaemolyticus or Staphylococcus aureus. The RNAi of MncSP could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. Phenoloxidase activity was also down-regulated in MncSP-silenced prawns. This study indicated that MncSP participated in the synthesis of AMPs and the activation of prophenoloxidase.

Identification, functional characterization and the potential role of variable lymphocyte receptor EsVLRA from Eriocheir sinensis in response to secondary challenge after Vibrio parahaemolyticus vaccine

Variable lymphocyte receptors (VLRs) play an important role via their antigen-special reorganization in jawless vertebrates (agnathans) adaptive immune response. In the present study, the open reading frame (ORF) of Eriocheir sinensis VLRA (designated as EsVLRA) was identified. EsVLRA comprised a 799-amino-acid polypeptide with one LRR_NT domain, thirteen LRR domains and one LRR_CT domain, which showed a high domain consistency of the VLR genes in lamprey (Petromyzon marinus). The transcript of EsVLRA was detected in all examined tissues with the highest level detected in hepatopancreas. Notably, the expression of EsVLRA in hepatopancreas, gonads, gill and intestine of male crabs was significantly higher than that in females. The recombinant EsVLRA exhibited strong bacteria-binding activity rather than antibacterial activity, suggesting its crucial role in immune recognition. Furthermore, 6 h earlier response and a significantly higher peak of EsVLRA mRNA expression was observed after challenge with live Vibrio parahaemolyticus (240.6-fold, P < 0.01, crabs receive secondary challenge after V. parahaemolyticus vaccine to the carbs only receive twice PBS injection, N = 6), compared with those only received first injection with formalin-inactivated V. parahaemolyticus (39.7-fold, P < 0.01, challenge 6 h to vaccination 12 h). The findings of this study together demonstrated that EsVLRA plays an important role in the immune system of E. sinensis, serving as a pattern recognition receptor and involving in the immune priming.

Molecular cloning, characterization, and expression of a C-type lectin from Scylla paramamosain, which might be involved in the innate immune response

C-type lectins (CTLs) have characteristic carbohydrate recognition domains (CRDs) and play important roles in the immune system. In the present study, a new CTL, SpCTL5, was identified from the hepatopancreas of the mud crab Scylla paramamosain. The open reading frame of SpCTL5 comprised 762 bp, encoding a polypeptide of 253 amino acids with a putative signaling peptide of 20 amino acids. The predicted SpCTL5 protein contained a single CRD. SpCTL5 transcripts were distributed in all examined tissues, with the highest level being detected in the hepatopancreas. Upon challenging with Vibrio alginolyticus, the mRNA levels of SpCTL5 in the hepatopancreas were up-regulated. The recombinant protein of SpCTL5 could agglutinate three Gram-positive bacteria and three Gram-negative bacteria in the presence of Ca²⁺. Furthermore, hemagglutination analysis showed that the recombinant protein of SpCTL5 can agglutinate rabbit erythrocytes. This study indicated that SpCTL5 acts as a pattern recognition receptor for the innate immune response which protects S. paramamosain from bacterial infection. Moreover, these findings also provide information to further our understanding of the innate immunology of invertebrates.

Functional characterization of two clip-domain serine proteases in the swimming crab Portunus trituberculatus

Clip domain serine proteases (cSPs), a family of multifunctional proteins, play a crucial role in innate immune system. Here, we report the functional characterization of two clip domain serine proteases (PtcSP1 and PtcSP3) from the swimming crab Portunus trituberculatus. The recombinant N-terminal clip domains and the C-terminal SP-like domains of PtcSP1 and PtcSP3 were expressed in Escherichia coli system, and assayed for various biological functions: protease activity, antimicrobial activity, bacterial clearance and microbial-binding activity. The recombinant SP-like domains of PtcSP1 and PtcSP3 exhibited trypsin-like protease activity, while their recombinant clip domains showed strong antibacterial activity and could bind to bacteria and yeast, suggesting the potential roles of PtcSP1 and PtcSP3 in immune defense and pattern recognition. Unlike PtcSP3, PtcSP1 revealed the opsonic activity as shown by a higher bacterial clearance rate of Vibrio alginolyticus coated with the combination of the recombinant clip domain and SP-like domain of PtcSP1 as compared with V. alginolyticus only. Knockdown of PtcSP1 or PtcSP3 by RNA interference resulted in a significant decrease of total phenoloxidase (PO) activity in crab, suggesting that PtcSP1 and PtcSP3 are involved in the proPO system. In addition, suppression of PtcSP1 or PtcSP3 changed the expression of PtALFs and complement-like components. All these findings suggest that PtcSP1 and PtcSP3 are multifunctional immune molecules and perform different protective functions in crab defense.

Two novel serine proteases from Scylla paramamosain involved in the synthesis of anti-lipopolysaccharide factors and activation of prophenoloxidase system

Serine proteases (SPs) are important in various immune responses, including prophenoloxidase (proPO) activation, antimicrobial peptides (AMPs) synthesis, and hemolymph coagulation in invertebrates. In this study, SP3 and SP5 of mud crab (Scylla paramamosain) were studied. SP3 and SP5 were expressed in all examined tissues (mainly in hemocytes), and are associated with the immune responses of mud crab to Vibrio parahemolyticus and Staphylococcus aureus, as well as interacted with TRAF6, and are involved in the activation of anti-lipopolysaccharide factors (ALFs) probably through the TLR/NF-κB pathway. Depletion of SP3 inhibited the expression of ALF1, ALF2, ALF3, and ALF6, while knockdown of SP5 significantly decreased ALF5, and ALF6. Furthermore, both SP5 and TRAF6 regulated the PO activity in the hemolymph of mud crab. Overexpression assay showed that both SP3 and SP5 could enhance the promoter activities of ALFs in mud crab. Taken together, the results of this study indicate that SP3 and SP5 might play important roles in the immune system of mud crab against pathogen invasion.

Molecular cloning of a C-type lectin from Portunus trituberculatus, which might be involved in the innate immune response

C-type lectin plays an important role in the innate immune response of crustaceans including Portunus trituberculatus which is an important marine species. In the present study, we cloned the full length of a C-type lectin (designated as PtCTL4) from P. trituberculatus via 3'RACE. The full length of the nucleic acid sequence has a length of 654 bp including an open reading frame (ORF) of 480 bp. PtCTL4 possesses conserved CTL features, while containing a CRD domain with Ca²⁺ binding site 2 and six conserved cysteine residues. Quantitative RT-PCR analysis showed that PtCTL4 expression level was highest in the hepatopancreas, while it was relatively low in other tissues such as hemocytes, eyestalk, muscle, and gonad. The expression level of PtCTL4 reached a maximum at 3 h after challenge with Vibrio alginolyticus, then decreased to the lowest level at 12 h, and returned to normal level at 48 h. Hemagglutination analysis showed that the recombinant PtCTL4 (rPtCTL4) can agglutinate rabbit erythrocyte. The rPtCTL4 can agglutinate Gram-positive bacteria (Bacillus aquimaris, Micrococcus lysodeik, and Staphylococcus aureus) and Gram-negative bacteria (Aeromonas hydrophila, V. alginolyticus, and Chryseobacterium indologenes) in the presence of Ca²⁺. This study indicated that PtCTL4 acts as a pattern recognition receptor in the innate immune response of P. trituberculatus.

A chymotrypsin-like serine protease from Portunus trituberculatus involved in pathogen recognition and AMP synthesis but not required for prophenoloxidase activation

Clip domain serine proteases (clip-SPs) play critical roles in various immune responses in arthropods, such as hemolymph coagulation, antimicrobial peptide (AMP) synthesis, cell adhesion and melanization. In the present study, we report the molecular and functional characterization of a clip domain serine protease (PtcSP2) from the swimming crab Portunus trituberculatus. The N-terminal clip domain and the C-terminal SP-like domain of PtcSP2 were expressed in Escherichia coli system, and assayed for their activities. Sequence similarity and phylogenetic analysis revealed that PtcSP2 may belong to the chymotrypsin family, which was confirmed by protease activity assay of the recombinant SP-like domain. The clip domain of PtcSP2 exhibited strong antibacterial activity and microbial-binding activity, suggesting the potential role in immune defense and recognition. Knockdown of PtcSP2 by RNA interference could significantly reduce PtcSP2 transcript levels, but neither decrease the total phenoloxidase (PO) activity in crab nor significantly alter the expression levels of serine protease inhibitors PtPLC and PtSerpin. These results indicate that PtcSP2 is not involved in the proPO system. However, suppression of PtcSP2 led to a significant change in the expression of AMP genes PtALFs and PtCrustin but not PtALF5. All these findings suggest that PtcSP2 is a multifunctional chymotrypsin-like serine protease and may participate in crab innate immunity by its antibacterial activity, immune recognition or regulation of AMP expression.

Characterization and functional analysis of a novel C-type lectin from the swimming crab Portunus trituberculatus

C-type lectins (CTLs) are a family of calcium-dependent carbohydrate-binding proteins. In the present study, a novel C-type lectin (designated as PtCTL1) was identified and characterized from Portunus trituberculatus. The full-length cDNA of PtCTL1 was of 702 bp, containing a 5' untranslated region (UTR) of 91 bp, a 3' UTR of 110 bp with a poly (A) tail, and an open reading frame (ORF) of 501 bp encoding a polypeptide of 166 amino acids with a putative signaling peptide of 21 amino acids. A C-type lectin carbohydrate-recognition domain (CRD) containing four conserved cysteines was identified in the amino acid sequence of PtCTL1. The cDNA fragment encoding the mature peptide of PtCTL1 was recombined into pET-21a(+) with a C-terminal hexa-histidine tag fused in-frame and expressed in Escherichia coli Origami (DE3). The recombinant PtCTL1 (rPtCTL1) can agglutinate all the tested bacteria, including three Gram-positive bacterial strains and three Gram-negative bacterial strains. In addition, erythrocyte agglutination and LPS-binding activity were observed in a Ca²⁺-dependent manner. The erythrocyte agglutination was inhibited by EDTA, indicating that PtCTL1 was Ca²⁺-dependent. The mRNA transcripts of PtCTL1 were detected mainly in the tissues of hepatopancreas and hemocytes and its levels were significantly up-regulated in hemocytes following Vibrio alginolyticus challenge. These results indicate that PtCTL1 may function as a pattern recognition receptor (PRR) for protecting P. trituberculatus from bacterial infection. Moreover, such findings also provide evidence for further understanding the innate immunology of invertebrate.

Changes of exoskeleton surface roughness and expression of crucial participation genes for chitin formation and digestion in the mud crab (Macrophthalmus japonicus) following the antifouling biocide irgarol

Irgarol is a common antifoulant present in coastal sediment. The mud crab Macrophthalmus japonicus is one of the most abundant of the macrobenthos in the costal environment, and its exoskeleton has a protective function against various environmental threats. We evaluated the effects of irgarol toxicity on the exoskeleton of M. japonicus, which is the outer layer facing the environment. We analyzed transcriptional expression of exoskeleton, molting, and proteolysis-related genes in the gill and hepatopancreas of these exposed M. japonicus. In addition, changes in survival and exoskeleton surface characteristics were investigated. In the hepatopancreas, mRNA expression of chitinase 1 (Mj-chi1), chitinase 4 (Mj-chi4), and chitinase 5 (Mj-chi5) increased in M. japonicus exposed to all concentrations of irgarol. Mj-chi1 and Mj-chi4 expressions from 1 to 10μgL(-1) were dose- and time-dependent. Ecdysteroid receptor (Mj-EcR), trypsin (Mj-Tryp), and serine proteinase (Mj-SP) in the hepatopancreas were upregulated in response to different exposure levels of irgarol at day 1, 4, or 7. In contrast, gill Mj-chi5, Mj-Tryp, and Mj-SP exhibited late upregulated responses to 10μgL(-1) irgarol compared to the control at day 7. Mj-chi1 showed early upregulation upon exposure to 10μgL(-1) irgarol and Mj-chi4 showed no changes in transcription in the gill. Gill Mj-EcR presented generally downregulated expression patterns. In addition, decreased survival and change of exoskeleton surface roughness were observed in M. japonicus exposed to the three concentrations of irgarol. These results suggest that exposure to irgarol induces changes in the exoskeleton, molting, and proteolysis metabolism of M. japonicus.

PtPLC, a pacifastin-related inhibitor involved in antibacterial defense and prophenoloxidase cascade of the swimming crab Portunus trituberculatus

Pacifastin-related inhibitor is a new family of serine protease inhibitors that regulate the proteolytic cascade in multiple biological processes. Contrary to the knowledge on the structure and inhibitory mechanism of pacifastin-like members in locust, very little is known about their functions. Here, we report the inhibitory activities in relation to the structural characteristics of pacifastin light chain (PtPLC) gene identified from the swimming crab Portunus trituberculatus. The mature PtPLC and five PLD-related domains with critical residues were expressed in Escherichia coli, and assayed for their activities. The recombinant PtPLC (rPtPLC) displayed inhibitory activities against trypsin and chymotrypsin in a dose dependent manner, with a preference for trypsin. Except for rPtPLC-D4, the other four rPtPLC-related domains could inhibit at least one of serine proteases. The enzyme specificity of PtPLC domains generally corresponded to the nature of the P1 residue at the reactive site. rPtPLC was able to inhibit the growth of Gram-negative bacteria Vibrio alginolyticus and Pseudomonas aeruginosa, but not the Gram-positive bacterium and fungus tested. Further phenoloxidase (PO) assay showed the rPtPLC could depress the crab proPO system activation in vitro, and lead to 72.8% inhibition of PO activity at the concentration of 9.11 μM. It also suppressed proPO activation induced by rPtcSP and rPtSPH1. As the first functional study of the recombinant PLC protein in crustaceans, the present results together indicate that PtPLC functions in the crab immune response possibly via inhibiting bacterial growth and regulating the proPO system.

PtSerpin from the swimming crab Portunus trituberculatus, a putative regulator of prophenoloxidase activation with antibacterial activity

Serpin or serine protease inhibitor is the largest family of protease inhibitors involved in many innate immune pathways, particularly the prophenoloxidase (proPO) activating system in arthropod. Here, we report the molecular and functional characterization of PtSerpin identified from the swimming crab Portunus trituberculatus. The genomic sequence encoding mature peptide of PtSerpin gene contained two exons of 84 and 1098 bp separated by one intron of 111 bp. The recombinant PtSerpin (rPtSerpin) with a predicted size of 44 kDa was expressed in Escherichia coli system, purified and assayed for its activities. The rPtSerpin exhibited inhibitory activity against trypsin in a dose-dependent manner, but did not affect chymotrypsin, which could define a role for PtSerpin as a trypsin inhibitor. The rPtSerpin could inhibit the growth of Gram-negative bacterium Vibrio alginolyticus, but not the tested Gram-positive bacterium and fungus. Further phenoloxidase (PO) assay showed PO activity was dramatically increased in hemocyte lysate supernatant of P. trituberculatus upon bacterial challenge. The rPtSerpin could depress the crab proPO system activation in vitro, and it could lead to 100% inhibition of PO activity under the concentration of 8.62 μM. Moreover, the rPtSerpin was able to inhibit the PO activity induced by rPtcSP and rPtSPH1. These results together indicate that PtSerpin is a potential trypsin inhibitor and may participate in crab innate immunity by the inhibition of bacterial growth and the regulation of proPO system.

Rare Earth Nanoprobes for Functional Biomolecular Imaging and Theranostics

Contrast agents designed to visualize the molecular mechanisms underlying cancer pathogenesis and progression have deepened our understanding of disease complexity and accelerated the development of enhanced drug strategies targeted to specific biochemical pathways. For the next generation probes and imaging systems to be viable, they must exhibit enhanced sensitivity and robust quantitation of morphologic and contrast features, while offering the ability to resolve the disease-specific molecular signatures that may be critical to reconstitute a more comprehensive portrait of pathobiology. This feature article provides an overview on the design and advancements of emerging biomedical optical probes in general and evaluates the promise of rare earth nanoprobes, in particular, for molecular imaging and theranostics. Combined with new breakthroughs in nanoscale probe configurations, and improved dopant compositions, and multimodal infrared optical imaging, rare-earth nanoprobes can be used to address a wide variety of biomedical challenges, including deep tissue imaging, real-time drug delivery tracking and multispectral molecular profiling.