Two duplicated chicken-type lysozyme genes in disc abalone Haliotis discus discus: molecular aspects in relevance to structure, genomic organization, mRNA expression and bacteriolytic function

Identification and antibacterial activity of a novel phage-type lysozyme from the freshwater mussel Hyriopsis cumingii

A cDNA encoding a phage-type lysozyme, designated as HcPLYZ, was successfully cloned from Hyriopsis cumingii. The full-length cDNA sequence of HcPLYZ was determined to be 896 base pairs in length. Analysis revealed the absence of a signal peptide at its N-terminus, and identified two highly conserved phage-type lysozyme activity sites, Glu20 and Asp29, within the deduced amino acid sequence of HcPLYZ. The results of the cloning and sequencing symbiotic bacteria in tissues were consistent with those obtained using tissue cDNA as the template, suggesting that HcPLYZ may originate a symbiotic bacterium. The expression levels of HcPLYZ mRNA exhibited significant variations across different tissues. Successful expression was induced using IPTG, and the native recombinant protein was subsequently purified through affinity chromatography employing Ni2+, and the optimal pH and temperature of which were determined to be 5.5 and 50 °C, respectively. Following exposure to Aeromonas hydrophila, there was a significant increase in the levels of HcPLYZ mRNA in the hemocytes, hepatopancreas, and gills. HcPLYZ was demonstrated the inhibition activity of 55% and 83% against Micrococcus lysodeikticus under pH 5.5 and 50 °C conditions, respectively. These results suggested that HcPLYZ possessed antibacterial activity against both A. hydrophila and M. lysodeikticus.

Identification and characterization of the c-type lysozyme gene from a marine fish, Bostrychus sinensis

In this study, a c-type lysozyme gene (BsLyzC) was identified and characterized from a marine fish, Bostrychus sinensis. The BsLyzC encodes 154 amino acids and contains a signal peptide of 17 amino acids, two catalytic residues and eight cysteine residues. The genomic DNA of BsLyzC consists of four exons and three introns. The BsLyzC shares high sequence similarity with c-type lysozyme from other fish species. The qPCR assays indicated that the BsLyzC exhibited a constitutive expression pattern in eleven examined tissues of healthy B. sinensis individuals. The transcripts of BsLyzC could be significantly induced after infection of Vibrio parahemolyticus in blood, spleen and head kidney. The optimal temperature and pH for recombinant BsLyzC (rBsLyzC) were found to be 50 °C and 6.0, respectively. The rBsLyzC exhibited antibacterial activities against two Gram-positive bacteria and two Gram-negative bacteria. These results indicate that the BsLyzC is involved in the antibacterial immunity of B. sinensis.

Comparative Characterization of Two cxcl8 Homologs in Oplegnathus fasciatus: Genomic, Transcriptional and Functional Analyses

CXCL8 (interleukin-8, IL-8) is a CXC family chemokine that recruits specific target cells and mediates inflammation and wound healing. This study reports the identification and characterization of two cxcl8 homologs from rock bream, Oplegnathus fasciatus. Investigation of molecular signature, homology, phylogeny, and gene structure suggested that they belonged to lineages 1 (L1) and 3 (L3), and designated Ofcxcl8-L1 and Ofcxcl8-L3. While Ofcxcl8-L1 and Ofcxcl8-L3 revealed quadripartite and tripartite organization, in place of the mammalian ELR (Glu-Leu-Arg) motif, their peptides harbored EMH (Glu-Met-His) and NSH (Asn-Ser-His) motifs, respectively. Transcripts of Ofcxcl8s were constitutively detected by Quantitative Real-Time PCR (qPCR) in 11 tissues examined, however, at different levels. Ofcxcl8-L1 transcript robustly responded to treatments with stimulants, such as flagellin, concanavalin A, lipopolysaccharide, and poly(I:C), and pathogens, including Edwardsiella tarda, Streptococcus iniae, and rock bream iridovirus, when compared with Ofcxcl8-L3 mRNA. The differences in the putative promoter features may partly explain the differential transcriptional modulation of Ofcxcl8s. Purified recombinant OfCXCL8 (rOfCXCL8) proteins were used in in vitro chemotaxis and proliferation assays. Despite the lack of ELR motif, both rOfCXCL8s exhibited leukocyte chemotactic and proliferative functions, where the potency of rOfCXCL8-L1 was robust and significant compared to that of rOfCXCL8-L3. The results, taken together, are indicative of the crucial importance of Ofcxcl8s in inflammatory responses and immunoregulatory roles in rock bream immunity.

Immune and xenobiotic responses of glutathione S-Transferase theta (GST-θ) from marine invertebrate disk abalone (Haliotis discus discus): With molecular characterization and functional analysis

Representing a multifunctional complex group of proteins, glutathione S- transferases (GSTs) play a major role in the phase II detoxification process in a wide range of organisms. This study focused on the potential detoxification ability of disk abalone (Haliotis discus discus) GST theta (AbGST-θ) under different stress conditions with special reference to post immune challenges. Characterization of AbGST-θ revealed with 226 amino acids, 26.6 kDa of predicted molecular mass and 8.9 of theoretical isoelectric point. As illustrated in the multiple sequence alignment, eight glutathione binding sites (G-sites) and ten substrate binding sites (H-sites) were identified in well-distinct N-terminal and C-terminal domains of AbGST-θ, respectively. AbGST-θ exhibited its highest sequence identity with Mizuhopecten yessoensis (59.1%) and the phylogenetic tree clearly positioned AbGST-θ with pre-defined GST-θ molluscan homologues. The AbGST-θ was highly expressed in the digestive tract of un-challenged abalones. Upon administering the challenge experiment, AbGST-θ showed significant modulations in their transcriptional levels depending on the time and the tissue type. The optimum temperature was 37 °C and optimum pH was 7.5 for AbGST-θ. The determined enzyme kinetic parameters of AbGST-θ showed low affinity towards 1-Chloro-2,4-dinitrobenzene (CDNB) and glutathione (GSH) as substrates. Nonetheless, with Cibacron blue IC₅₀ (half maximal inhibitory concentration) was calculated to be 0.08 μM while observing 100% inhibition with 100 μM. Furthermore, AbGST-θ resulted in significant protection ability towards H₂O₂, CdCl_2, and ZnCl₂ in the disk diffusion assay. Collectively, this study provides evidences for the detoxification ability and the immunological host defensive capability of AbGST-θ in disk abalone.

Molecular cloning, expression and antibacterial activity of goose-type lysozyme gene in Microptenus salmoides

It is well known that lysozymes are key proteins to teleosts in the innate immune system and possess high bactericidal properties. In the present study, a g-type lysozyme gene was cloned from Microptenus salmoides. The g-type sequence consisted of 582 bp, which translated into a 193 amino acid (AA) protein (GenBank accession no: MH087462). The predicted molecular weight and theoretical isoelectric point were 21.36 kDa and 6.91 respectively and no signal peptide was observed. The qRT-PCR analysis showed that the g-type lysozyme gene was differentially expressed in various tissues under normal conditions and the highest g-type lysozyme level was observed in liver, gill and spleen while there seemed to be low expression in the muscle, heart and head-kidney. The expression of g-type lysozyme was differentially upregulated in the spleen, gill and intestine after stimulation with heat stress and Aeromonas hydrophila (A. hydrophila). Under heat stress and A. hydrophila injection, the g-type lysozyme mRNA levels all in spleens, gill and intestine tissues increased significantly (P < 0.05), with the maximum levels attained at 12 h, 24 h (or 12 h) and 24 h. Thereafter, they all decreased significantly (P < 0.01) and the expression in gill returned to nearly the basal value within 72 h. Those results suggested that g-type lysozyme was involved in the immune response to heat stress and bacterial challenge. The cloning and expression analysis of the g-type lysozyme provide theoretical basis to further study the mechanism of anti-adverseness in Microptenus salmoides. The g-type lysozyme gene perhaps also played an important role in the immune responses against bacterial invasion.

Molecular, transcriptional and functional insights into duplicated goose-type lysozymes from Sebastes schlegelii and their potential immunological role

Black rockfish (Sebastes schlegelii), an important aquaculture species in Korea, has been affected by bacterial diseases leading to a drastic decline in production. Goose-type lysozyme (LysG) is a key enzyme of the innate immune system to eradicate bacterial infections. In this study, two isoforms of LysG from black rockfish, designated as RfLysG1 and RfLysG2, have been identified and characterized at the molecular, transcriptional, and functional levels. The deduced amino acid sequences had the LysG family characteristics and exhibited conserved properties, including active residues and domains. The cDNA sequences of RfLysG1 and RfLysG2 were 1514 bp and 900 bp in length, respectively. The 567-bp open reading frame (ORF) of RfLysG1 encoded a protein of 188 amino acids with molecular mass 20.11 kDa, and the 600-bp ORF of RfLysG2 encoded a polypeptide with 199 amino acids and molecular mass of 22.19 kDa. Homology studies indicated that RfLysG1 showed the highest identity (84.6%) with LysG-B of Oplegnathus fasciatus, while RfLysG2 showed the highest identity (74.4%) with LysG of Siniperca chuatsi. Both sequences possessed a soluble lytic trans-glycosylase domain. Both lacked signal peptide and they were not identified as proteins secreted by non-classical pathway by the SecretomeP server. Transcriptional analysis of the two genes showed constitutive expression, where both genes were highly expressed in blood under normal physiological conditions. In response to the immune challenges lipopolysaccharide (LPS), Streptococcus iniae, and poly I:C injection, the expression of RfLysG1 and RfLysG2 was significantly upregulated in blood and spleen tissues in a time-dependent manner. Turbidimetric assays indicated that both recombinant proteins tagged with maltose-binding protein (MBP) were reactive against several Gram-positive and Gram-negative bacteria, but MBP was inactive. Optimum temperatures for the recombinant RfLysG1 and RfLysG2 were 40 °C and 50 °C, respectively, and both were highly active at pH 3.0. The results provide evidence for the vital immunological role and bacteriolytic potential of RfLysG1 and RfLysG2.

Molecular characterization, expression and antimicrobial activities of two c-type lysozymes from manila clam Venerupis philippinarum

Lysozymes play an important role in the innate immune responses with which mollusks respond to bacterial invasion through its lytic activity. In the present study, two c-type lysozymes (designed as VpCLYZ-1 and VpCLYZ-2, respectively) were identified and characterized from the manila clam Venerupis philippinarum. The full-length cDNA of VpCLYZ-1 and VpCLYZ-2 was of 629 and 736 bp, encoding a polypeptide of 156 and153 amino acid residues, respectively. The deduced amino acid sequences of VpCLYZs showed high similarity to other known invertebrate c-type lysozymes. Multiple alignments and phylogenetic relationship strongly suggested that VpCLYZ-1 and VpCLYZ-2 belonged to the c-type lysozyme family. Both VpCLYZ-1 and VpCLYZ-2 transcripts were constitutively expressed in a wide range of tissues with different levels. The VpCLYZ-1 transcript was dominantly expressed in hepatopancreas and hemocytes, while VpCLYZ-2 transcript was mainly expressed in the tissues of hepatopancreas and gills. Both the mRNA expression of VpCLYZ-1 and VpCLYZ-2 was significantly up-regulated at 12 h post Vibrio anguillarum challenge. The recombinant VpCLYZ-1 and VpCLYZ-2 (designed as rVpCLYZ-1 and rVpCLYZ-2) exhibited lytic activity against all tested bacteria, and rVpCLYZ-1 showed higher activities than rVpCLYZ-2 in killing Micrococcus luteus and V. anguillarum. Overall, our results suggested that VpCLYZ-1 and VpCLYZ-2 belonged to the c-type lysozyme family, and played important roles in the immune responses of manila clam, especially in the elimination of pathogens.

Molecular characterization and antibacterial activity of a phage-type lysozyme from the Manila clam, Ruditapes philippinarum

A phage-type lysozyme, designed as RpPLYZ, was cloned and characterized from the clam Ruditapes philippinarum. The full-length cDNA of RpPLYZ was of 699 bp with an open reading frame (ORF) of 534 bp, encoding a polypeptide of 177-amino acid with a calculated molecular mass of 19.6 kDa and an isoelectric point of 9.05. Multiple alignments and phylogenetic analysis strongly suggested that RpPLYZ was a new member of the phage-type lysozyme family. The mRNA transcript of RpPLYZ was found to be constitutively expressed in a wide range of tissues and mainly in hemocytes and mantle. The relative expression of RpPLYZ mRNA in hemocytes was significantly up-regulated at 6, 24, 48 and 72 h after Vibrio anguillarum challenge. The recombinant RpPLYZ (rRpPLYZ) showed high activity against Entherobacter cloacae and Staphyloccocus aureus, and less effective towards Entherobacter aerogenes and V. anguillarum. Moreover, the optimal pH, temperature and ionic strength for rRpPLYZ activity was determined to be 5.5, 50 °C and 5 mM, respectively. These results suggested that RpPLYZ was a member of the phage-type lysozyme family and perhaps played an important role in the immune responses against bacterial invasion.

Molecular cloning, inducible expression and antibacterial analysis of a novel i-type lysozyme (lyz-i2) in Pacific white shrimp, Litopenaeus vannamei

The full-length cDNA coding for a novel invertebrate (i-type) lysozyme was identified in Pacific white shrimp (Litopenaeus vannamei). The newly obtained L. vannamei lysozyme is similar to the Penaeus monodon i-type lysozyme 2, but it is distant from the known L. vannamei c-type lysozyme and i-type lysozyme 1 in protein sequence; therefore, it was defined as L. vannamei i-type lysozyme 2 (lyz-i2). Expression of L. vannamei lyz-i2 transcripts were ubiquitously detected in all tissues we selected, with the highest abundance observed in the hemolymph. Challenge with Vibrio harveyi might elicit L. vannamei lyz-i2 mRNA expression in the hepatopancreas, intestine, muscle, gill and hemolymph. In the themolymph, specifically, the stimulatory effects of Vibrio and lipopolysaccharide (LPS) on lyz-i2 transcript levels were durable and transient, respectively; while Polyinosinic:polycytidylic acid [Poly (I:C)] treatment did not affect lyz-i2 expression. L. vannamei lyz-i2 recombinant protein was generated in an Escherichia coli system. By lysoplate and turbidimetric assays, the L. vannamei lyz-i2 recombinant protein showed a broad spectrum of antimicrobial properties with high activities against Micrococcaceae lysodeikticus and various Vibrio species and relatively low activity against E. coli. In conclusion, L. vannamei lyz-i2 might be a potent antibacterial protein with a role in innate immunity in Penaeid shrimp.

A molluscan calreticulin ortholog from Haliotis discus discus: Molecular characterization and transcriptional evidence for its role in host immunity

Calreticulin (CALR), a Ca(2+) binding chaperone of the endoplasmic reticulum (ER) and mainly involved in Ca(2+) storage and signaling. In this study, we report the molecular characterization and immune responses of CALR homolog from disk abalone (AbCALR). The full length AbCALR cDNA (1837 bp) had an ORF of 1224 bp. According to the multiple alignments analysis, N- and P-domains were highly conserved in all the selected members of CALRs. In contrast, the C-domain which terminated with the characteristic ER retrieval signal (HDEL) was relatively less conserved. The phylogenetic analysis showed that all the selected molluscan homologs clustered together. Genomic sequence of AbCALR revealed that cDNA sequence was dispersed into ten exons interconnected with nine introns. AbCALR mRNA expression shows the significant (P < 0.05) up-regulation of AbCALR transcripts in hemocytes upon bacterial (Listeria monocytogenes and Vibrio parahaemolyticus), viral (Viral haemorrhagic septicaemia virus; VHSV) and immune stimulants (LPS and poly I:C) challenges at middle and/or late phases. These results collectively implied that AbCALR is able to be stimulated by pathogenic signals and might play a potential role in host immunity.

Molecular characterization and expressing analysis of the c-type and g-type lysozymes in Qihe crucian carp Carassius auratus

Lysozyme as an important nonspecific immune factor, can kill bacteria by hydrolyzing β-1,4-glycosidic linkages of peptidoglycan layer, and plays an important role in innate immune response against pathogen infection. In the present study, we report molecular cloning, tissue distribution and functional characterization of the c-type and g-type lysozymes in Qihe crucian carp Carassius auratus (designated as Ca-clys and Ca-glys, respectively). The full-length of Ca-clys and Ca-glys cDNA were cloned using RT-PCR and RACE methods. Catalytic and other conserved residues, required for functionality, were identified by multiple sequence alignment and structure predicted. The findings indicating the Ca-clys with signal peptide sequence, while the Ca-glys without, imply that the two isozymes function in different sites of cell. Phylogenetic analysis revealed that Ca-clys and Ca-glys genes evolve at different rates. Moreover, spatial expression analysis showed that Ca-clys transcript was most abundant in kidney and least in gill. However, the expression level of Ca-glys was significantly lower compared with Ca-clys in various tissues, which was the most abundant in spleen and least in brain. After intraperitoneal injection with A. hydrophila and lipopolysaccharide (LPS), the mRNA levels of Ca-clys and Ca-glys were generally up-regulated in liver and gill, but indicated the different expression changes in spleen, kidney and head kidney. With regard to the lysozyme activity, it was showed that the total enzyme activities generally increased in liver, gill, spleen, and head kidney after stimulation. These results confirmed that both Ca-clys and Ca-glys play an important role in non-specific immunity after A. hydrophila invasion. In this study, it was speculated that expressions of Ca-clys and Ca-glys were regulated in different patterns against pathogens.

An invertebrate signal transducer and activator of transcription 5 (STAT5) ortholog from the disk abalone, Haliotis discus discus: Genomic structure, early developmental expression, and immune responses to bacterial and viral stresses

Signal transducer and activator of transcription (STAT) family members are key signaling molecules that transduce cellular responses from the cell membrane to the nucleus upon Janus kinase (JAK) activation. Although seven STAT members have been reported in mammals, very limited information on STAT genes in molluscans is available. In this study, we identified and characterized a STAT paralog that is homologous to STAT5 from the disk abalone, Haliotis discus discus, and designated as AbSTAT5. Comparison of the deduced amino acid sequence for AbSTAT5 (790 amino acids) with other counterparts revealed conserved residues important for functions and typical domain regions, including the N-terminal domain, coiled-coil domain, DNA-binding domain, linker domain, and Src homology 2 (SH2) domains as mammalian counterparts. Analysis of STAT phylogeny revealed that AbSTAT5 was clustered with the molluscan subgroup in STAT5 clade with distinct evolution. According to the genomic structure of AbSTAT5, the coding sequence was distributed into 20 exons with 19 introns. Immunologically essential transcription factor-binding sites, such as GATA-1, HNF, SP1, C/EBP, Oct-1, AP1, c-Jun, and Sox-2, were predicted at the 5'-proximal region of AbSTAT5. Expression of AbSTAT5 mRNA was detected in different stages of embryonic development and observed at considerably higher levels in the morula and late veliger stages. Tissue-specific expressional studies revealed that the highest level of AbSTAT5 transcripts was detected in hemocytes, followed by gill tissues. Temporal expressions of AbSTAT5 were analyzed upon live bacterial (Vibrio parahemolyticus and Listeria monocytogenes), viral (viral hemorrhagic septicemia virus), and pathogen-associated molecular pattern (lipopolysaccharides and Poly I:C) stimulations, and significant elevations indicated immune modulation. These results suggest that AbSTAT5 may be involved in maintaining innate immune responses from developmental to adult stages in the disk abalone. Further, this study provides a basis for structural and functional exploration of STAT members in the invertebrate JAK/STAT signaling pathway.

Ferritin from the Pacific abalone Haliotis discus hannai: Analysis of cDNA sequence, expression, and activity

Ferritin plays an important role in iron homeostasis due to its ability to bind and sequester large amounts of iron. In this study, the gene encoding a ferritin (HdhFer2) was cloned from Pacific abalone (Haliotis discus hannai). The full-length cDNA of HdhFer2 contains a 5'-UTR of 121 bp, an ORF of 516 bp, and a 3'-UTR of 252 bp with a polyadenylation signal sequence of AATAAA and a poly(A) tail. It also contains a 31 bp iron-responsive element (IRE) in the 5'-UTR position, which is conserved in many ferritins. HdhFer2 consists of 171 amino acid residues with a predicted molecular weight (MW) ∼19.8 kDa and a theoretical isoelectric point (PI) of 4.84. The deduced amino acid sequence of HdhFer2 contains two ferritin iron-binding region signatures (IBRSs). HdhFer2 mRNA was detected in a wide range of tissues and was dominantly expressed in the gill. Infection with the bacterial pathogen Vibrio anguillarum significantly upregulated HdhFer2 expression in a time-dependent manner. Recombinant HdhFer2 (rHdhFer2) purified from Escherichia coli was able to bind ferrous iron in a concentration-dependent manner. In summary, these results suggest that HdhFer2 is a crucial protein in the iron-withholding defense system, and plays an important role in the innate immune response of abalone.

Identification and characterization of a novel phage-type like lysozyme from Manila clam, Ruditapes philippinarum

A novel lysozyme gene (RpLysPh) with high similarity to the bacteriophage lysozymes was identified in Manila clam, Ruditapes philippinarum. The full length cDNA of RpLysPh is 828bp and contains a 462bp open reading frame (ORF) that codes for a 154 amino acid protein. Multiple sequence alignment analysis revealed that the three residues essential for catalytic activity in phage-type lysozyme (Glu(20), Asp(29), and Thr(35)) are conserved in RpLysPh. The comparison of the 3D models of RpLysPh and Coxiella burnetii lysozyme also suggested that the active sites involved in the binding of substrate have similar conformations. Phylogenetic analysis suggested that RpLysPh shares a similar origin with the bacterial phage-type lysozyme group. The highest level of expression of RpLysPh was observed in hemocytes, followed by mantle. Induction of RpLysPh expression was observed in gills in response to lipopolysaccharide (LPS), peptidoglycan (PGN), polyinosinic-polycytidylic acid (Poly(I:C)), and whole glucan particles (WGP) challenge. The recombinant protein of RpLysPh showed antibacterial activity against both Gram-positive and Gram-negative bacteria.

Evidences for the involvement of an invertebrate goose-type lysozyme in disk abalone immunity: cloning, expression analysis and antimicrobial activity

Lysozymes are ubiquitously distributed enzymes with hydrolytic activity against bacterial peptidoglycan and function to protect organisms from microbial pathogens. In this study, an invertebrate goose-type lysozyme, designated as abLysG, was identified in the disk abalone, Haliotis discus discus. The full-length cDNA of abLysG was 894 bp in length with an open reading frame of 789 bp encoding a polypeptide of 263 amino acids containing a signal peptide and a characteristic soluble lytic transglycosylase domain. Six cysteine residues and two catalytic residues (Glu(142) and Asp(168)) conserved among molluscs were also identified. The 3D homology structural models of abLysG and hen egg white lysozyme had similar conformations of the active sites involved in the binding of substrate. BAC sequence data revealed that the genomic structure of disk abalone g-type lysozyme comprises 7 exons with 6 intervening introns. The deduced amino acid sequence of abLysG shared 45.2-61.6% similarity with those of other molluscs and vertebrates. The TFSEARCH server predicted a variety of transcription factor-binding sites in the 5'-flanking region of the abLysG gene, some of which are involved in transcriptional regulation of the lysozyme gene. abLysG expression was detected in multiple tissues with the highest expression in mantle. Moreover, qPCR analysis of abLysG mRNA expression demonstrated significant up-regulation in gill in response to infection by live bacteria (Vibrio parahaemolyticus and Listeria monocytogenes), virus (viral hemorrhagic septicemia) and bacterial mimics (LPS and PGN). Expression of the recombinant disk abalone g-type lysozyme in Escherichia coli BL21, demonstrated its bacteriolytic activity against several Gram-negative and Gram-positive bacterial species. Collectively these data suggest that abLysG is an antimicrobial enzyme with a potential role in the disk abalone innate immune system to protect it from bacterial and viral infections.