Evolution of the vertebrate goose-type lysozyme gene family

Characterization and expression patterns of lysozymes reveal potential immune functions during male pregnancy of seahorse

Seahorses are one of the most amazing ovoviviparous fishes in the ocean because males, and not females, have evolved a brood pouch for incubating embryos. During male pregnancy, paternal seahorses need to develop effective immune protection for embryos in the brood pouch from potential infection by pathogens. Lysozymes (Lyz) are a group of antibacterial enzymes of the innate immune system that play an important role in resisting pathogen invasion. However, the immune function of lysozymes in the brood pouch of the pregnancy-lined seahorse (Hippocampus erectus) remains unknown. In this study, we found three different lysozymes in the lined seahorse: HeLyzC, HeLyzG1, and HeLyzG2. Synteny analysis revealed that HeLyzG1 and HeLyzG2 were generated by species-specific expansion rather than tandem duplication. Tissue expression patterns showed that the highest mRNA expression levels of the three lysozymes occurred in the brood pouches. Immunostimulation-induced expression analysis showed that all three HeLyzs in the brood pouches up-regulated their mRNA expression levels after Vibrio parahaemolyticus infection, but only the HeLyzG2 was upregulated after Poly(I:C) injection. Similarly, except for HeLyzC, upregulated expressions of HeLyzG1 and HeLyzG2 were found quickly in brood pouches injected with LPS. The upregulated levels of HeLyzC and HeLyzG2 in brood pouches during pregnancy were significantly higher than those in non-pregnancy, implying that seahorse lysozymes might function in the immune defense in brood pouches during pregnancy. In addition, the expression levels of HeLyzs were low in embryos in the brood pouch but significantly increased in neonates. This implies that embryos in the brood pouch might not necessarily express more lysozymes by themselves due to paternal immune protection. In conclusion, our study demonstrated that HeLyzs play an important role in immune protection during male seahorse gestation, and the synergistic effect of multiple HeLyzs may contribute to improved neonatal survival.

Lysozymes in Fish

In recent years, the deterioration of the aquaculture ecological environment has led to a high incidence of fish diseases. Lysozymes, important antimicrobial enzymes, play an important role in the innate immune system of fish. The studies of fish lysozymes benefit the control of fish infections caused by pathogens. In this review, we reviewed recent progress in fish lysozymes, including their classification, structural characteristics, biological functions and mechanisms, tissue distributions, and properties of their recombinant proteins, which will help us to systematically understand the fish lysozymes and facilitate their applications in the fields of food and agriculture.

Parallel Independent Losses of G-Type Lysozyme Genes in Hairless Aquatic Mammals

Lysozyme enzymes provide classic examples of molecular adaptation and parallel evolution, however, nearly all insights to date come from chicken-type (c-type) lysozymes. Goose-type (g-type) lysozymes occur in diverse vertebrates, with multiple independent duplications reported. Most mammals possess two g-type lysozyme genes (Lyg1 and Lyg2), the result of an early duplication, although some lineages are known to have subsequently lost one copy. Here we examine g-type lysozyme evolution across >250 mammals and reveal widespread losses of either Lyg1 or Lyg2 in several divergent taxa across the mammal tree of life. At the same time, we report strong evidence of extensive losses of both gene copies in cetaceans and sirenians, with an additional putative case of parallel loss in the tarsier. To validate these findings, we inspected published short-read data and confirmed the presence of loss of function mutations. Despite these losses, comparisons of selection pressures between intact g- and c-type lysozyme genes showed stronger purifying selection in the former, indicative of conserved function. Although the reasons for the evolutionary loss of g-type lysozymes in fully aquatic mammals are not known, we suggest that this is likely to at least partially relate to their hairlessness. Indeed, although Lyg1 does not show tissue-specific expression, recent studies have linked Lyg2 expression to anagen hair follicle development and hair loss. Such a role for g-type lysozyme would explain why the Lyg2 gene became obsolete when these taxa lost their body hair.

Fish lysozyme gene family evolution and divergent function in early development

Lysozymes are an ancient group of antimicrobial enzymes of the innate immune system. Here we provide a comparative analysis of the evolution and function of lysozymes during early development in fish, the most speciose vertebrate group. In fishes, lineage and species-specific evolution of both C-type (chicken or conventional) and G-type (goose type) genes occurred. Phylogenetic analysis revealed that the teleost lysozyme G-type members group with the tetrapod homologues but the teleost C-type form three different clusters with the tetrapods. Most of the teleost C-type cluster with tetrapod Lyz but there are some that group with the mammalian Lyzl1/2 and LALBA. This suggests that early in gnathostome evolution these genes already existed and that lyzl1/2 and lalba genes are present in fish and tetrapods. Gene synteny analysis to confirm sequence orthologies failed to identify conserved genome regions between teleosts and other vertebrates lysozyme gene regions suggesting that in the ancestral bony fish genome lyz, lyzl1/2, lalba and lyg precursor genes were transposed to different chromosome regions. The homologue of the mammalian lactalbumin (LALBA) gene was identified for the first time in teleosts and was expressed in skin and during egg and larval development. Lysozyme activity was detected in teleost eggs and varied between species and in the gilthead sea bream lyg and lalba transcript abundance differed in eggs and larvae from different brood stock suggesting differences exist in maternal innate immune protection.

Molecular characterization and expression analysis of the chicken-type and goose-type lysozymes from totoaba (Totoaba macdonaldi)

Lysozymes play a key role in innate immune response to bacterial pathogens, catalyzing the hydrolysis of the peptidoglycan layer of bacterial cell walls. In this study, the genes encoding the c-type (TmLyzc) and g-type (TmLyzg) lysozymes from Totoaba macdonaldi were cloned and characterized. The cDNA sequences of TmLyzg and TmLyzc were 582 and 432 bp, encoding polypeptides of 193 and 143 amino acids, respectively. Amino acid sequences of these lysozymes shared high identity (60-90%) with their counterparts of other teleosts and showed conserved functional-structural signatures of the lysozyme superfamily. Phylogenetic analysis indicated a close relationship with their vertebrate homologues but distinct evolutionary paths for each lysozyme. Expression analysis by qRT-PCR revealed that TmLyzc was expressed in stomach and pyloric caeca, while TmLyzg was highly expressed in stomach and heart. These results suggest that both lysozymes play important roles in defense of totoaba against bacterial infections or as digestive enzyme.

Expression of β-1,4-galactosyltransferases during Aging in Caenorhabditis elegans

BACKGROUND

Altered plasma activity of β-1,4-galac-tosyl-transferases (B4GALTs) is a novel candidate biomarker of human aging. B4GALT1 is assumed to be largely responsible for this activity increase, but how it modulates the aging process is unclear at present.

OBJECTIVES

To determine how expression of B4GALT1 and other B4GALT enzymes changes during aging of an experimentally tractable model organism, Caenorhabditis elegans.

METHODS

Targeted analysis of mRNA levels of all 3 C. elegans B4GALT family members was performed by qPCR in wild-type and in long-lived daf-2 (insulin/IGF1-like receptor)-deficient or germline-deficient animals.

RESULTS

bre-4 (B4GALT1/2/3/4) is the only B4GALT whose expression increases during aging in wild-type worms. In addition, bre-4 levels also rise during aging in long-lived daf-2-deficient worms, but not in animals that are long-lived due to the lack of germline stem cells. On the other hand, expression of sqv-3 (B4GALT7) and of W02B12.11 (B4GALT5/6) appears decreased or constant, respectively, in all backgrounds during aging.

CONCLUSIONS

The age-dependent bre-4 mRNA increase in C. elegans parallels the age-dependent B4GALT activity increase in humans and is consistent with C. elegans being a suitable experimental organism to define potentially conserved roles of B4GALT1 during aging.

Activity of mammalian peptidoglycan-targeting immunity against Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most important opportunistic pathogens, whose clinical relevance is not only due to the high morbidity/mortality of the infections caused, but also to its striking capacity for antibiotic resistance development. In the current scenario of a shortage of effective antipseudomonal drugs, it is essential to have thorough knowledge of the pathogen's biology from all sides, so as to find weak points for drug development. Obviously, one of these points could be the peptidoglycan, given its essential role for cell viability. Meanwhile, immune weapons targeting this structure could constitute an excellent model to be taken advantage of in order to design new therapeutic strategies. In this context, this review gathers all the information regarding the activity of mammalian peptidoglycan-targeting innate immunity (namely lysozyme and peptidoglycan recognition proteins), specifically against P. aeruginosa. All the published studies were considered, from both in vitro and in vivo fields, including works that envisage these weapons as options not only to potentiate their innate effects within the host or for use as exogenously administered treatments, but also harnessing their inflammatory and immune regulatory capacity to finally reduce damage in the patient. Altogether, this review has the objective of anticipating and discussing whether these innate immune resources, in combination or not with other drugs attacking certain P. aeruginosa targets leading to its increased sensitization, could be valid therapeutic antipseudomonal allies.

Molecular cloning, expression analyses and functional characterization of a goose-type lysozyme gene from Bostrychus sinensis (family: Eleotridae)

In this study, we sequenced and characterized the goose-type lysozyme gene, termed as BsLysG, from the Chinese black sleeper (Bostrychus sinensis). The BsLysG encodes 196 amino acids and contains a soluble bacterial lytic transglycosylases domain, three catalytic residues (Glu⁷², Asp⁸⁵ and Asp¹⁰²) and the GLMQ motif (Gly⁹⁷, Leu⁹⁸, Met⁹⁹ and Gln¹⁰⁰). No signal peptide was observed in the BsLysG protein. The genomic DNA of BsLysG contains five exons and four introns. The sequence analyses showed that the BsLysG exhibits high similarity with LysG from other fishes. Phylogenetic analyses showed that the BsLysG is clustered together with its counterparts from other teleost fishes. The Real-time PCR analyses showed that the BsLysG was found to be ubiquitously expressed in ten examined organs in Chinese black sleeper, with predominant expression in spleen, followed by head kidney and peripheral blood. Expression analyses showed that the BsLysG was significantly upregulated in vivo after either pathogen Vibrio parahemolyticus infection or poly (I:C) challenge in peripheral blood, head kidney, liver and spleen organs. The purified recombinant BsLysG (rBsLysG) has optimal activity at 35 °C and pH 5.5. The rBsLysG exhibited antimicrobial activity against two Gram-positive bacteria (Micrococcus lysodeikticus and Staphylococcus aureus) and two Gram-negative bacteria (Escherichia coli and V. parahemolyticus). The Scanning electron microscope (SEM) imaging analyses showed that the rBsLysG-treated V. parahemolyticus cells displayed morphological deformation. These results indicate that the BsLysG is involved in host immune defense against bacterial infection.

A Comparison of the Innate and Adaptive Immune Systems in Cartilaginous Fish, Ray-Finned Fish, and Lobe-Finned Fish

The immune system is composed of two subsystems-the innate immune system and the adaptive immune system. The innate immune system is the first to respond to pathogens and does not retain memory of previous responses. Innate immune responses are evolutionarily older than adaptive responses and elements of innate immunity can be found in all multicellular organisms. If a pathogen persists, the adaptive immune system will engage the pathogen with specificity and memory. Several components of the adaptive system including immunoglobulins (Igs), T cell receptors (TCR), and major histocompatibility complex (MHC), are assumed to have arisen in the first jawed vertebrates-the Gnathostomata. This review will discuss and compare components of both the innate and adaptive immune systems in Gnathostomes, particularly in Chondrichthyes (cartilaginous fish) and in Osteichthyes [bony fish: the Actinopterygii (ray-finned fish) and the Sarcopterygii (lobe-finned fish)]. While many elements of both the innate and adaptive immune systems are conserved within these species and with higher level vertebrates, some elements have marked differences. Components of the innate immune system covered here include physical barriers, such as the skin and gastrointestinal tract, cellular components, such as pattern recognition receptors and immune cells including macrophages and neutrophils, and humoral components, such as the complement system. Components of the adaptive system covered include the fundamental cells and molecules of adaptive immunity: B lymphocytes (B cells), T lymphocytes (T cells), immunoglobulins (Igs), and major histocompatibility complex (MHC). Comparative studies in fish such as those discussed here are essential for developing a comprehensive understanding of the evolution of the immune system.

Evolution of digestive enzymes and dietary diversification in birds

As the most species-rich class of tetrapod vertebrates, Aves possesses diverse feeding habits, with multiple origins of insectivory, carnivory, frugivory, nectarivory, granivory and omnivory. Since digestive enzymes mediate and limit energy and nutrient uptake, we hypothesized that genes encoding digestive enzymes have undergone adaptive evolution in birds. To test this general hypothesis, we identified 16 digestive enzyme genes (including seven carbohydrase genes (hepatic amy, pancreatic amy, salivary amy, agl, g6pc, gaa and gck), three lipase genes (cyp7a1, lipf and pnlip), two protease genes (ctrc and pgc), two lysozyme genes (lyz and lyg) and two chitinase genes (chia and chit1)) from the available genomes of 48 bird species. Among these 16 genes, three (salivary amy, lipf and chit1) were not found in all 48 avian genomes, which was further supported by our synteny analysis. Of the remaining 13 genes, eight were single-copy and five (chia, gaa, lyz, lyg and pgc) were multi-copy. Moreover, the multi-copy genes gaa, lyg and pgc were predicted to exhibit functional divergence among copies. Positively selected sites were detected in all of the analyzed digestive enzyme genes, except agl, g6pc, gaa and gck, suggesting that different diets may have favored differences in catalytic capacities of these enzymes. Furthermore, the analysis also revealed that the pancreatic amylase gene and one of the lipase genes (cyp7a1) have higher ω (the ratio of nonsynonymous to the synonymous substitution rates) values in species consuming a larger amount of seeds and meat, respectively, indicating an intense selection. In addition, the gck carbohydrase gene in species consuming a smaller amount of seeds, fruits or nectar, and a lipase gene (pnlip) in species consuming less meat were found to be under relaxed selection. Thus, gene loss, gene duplication, functional divergence, positive selection and relaxed selection have collectively shaped the evolution of digestive enzymes in birds, and the evolutionary flexibility of these enzymes may have facilitated their dietary diversification.

Identification and functional characterization of a g-type lysozyme gene of Labeo rohita, an Indian major carp species

Lysozyme, an important secretory innate immune component, possesses antimicrobial activity against broad spectrum of bacteria and viruses. In the present study, complete CDs (558 bps) of g-type lysozyme of rohu (Labeo rohita) was amplified and translated for a putative protein of 185 amino acids. The domain architecture and tertiary structure was also predicted for the protein. Its expression profile was studied in three infection models (bacteria: Aeromonas hydrophila, poly I:C, a dsRNA viral analogue and an ectoparasite: Argulus siamensis) in liver and kidney tissues of rohu. An up-regulation of 630-fold and 420-fold of the gene was observed at 48 h in liver and anterior kidney tissues respectively, after A. hydrophila infection. Significant increase in transcript level was noticed in both liver (0.8-fold) and kidney (480-fold) after 1 h and 12 h of poly I:C induction, respectively. Similarly, expression of lysozyme g transcripts was increased 6000-fold after 7 d of A. siamensis infection in liver tissue. The recombinant protein of g-type lysozyme of rohu (rLr-lysG) of 20.19 kDa was produced in Escherichia coli system and the lysozyme activity of rLr-lysG was found to be most active at pH 6.0 and temperature 35 °C. The potential lytic activity was found to be against A. hydrophila (U_L = 0.53) followed by for E. tarda (U_L = 0.45) whereas the lytic activity was the least against S. aureus (U_L = 0.35) and M. lysodeikticus (U_L = 0.34), at pH 6.0 and temperature 35 °C. The normal serum level of protein was estimated using indirect ELISA and was found to be very low (0.12-0.15 μg/ml). These results suggested that g-type lysozyme of rohu might be a potent immunostimulant against microbial infections, with a major role in innate immunity.

Efficient production of human goose-type lysozyme 2 in the methylotrophic yeast Pichia pastoris

Infectious diseases caused by antibiotic multidrug-resistant microorganisms are major causes of morbidity and mortality in humans. Hence, there is an urgent need to search for new antimicrobial agents. Initially known as a defensive effector in the innate immunity of certain organs of the human body, human goose-type lysozyme 2 (hLysG2) has been shown to possess therapeutically useful potential against multidrug-resistant microorganisms. Developing a novel strategy for large-scale production that provides high yields of this protein with high purity, quality, and potency is critical for pharmaceutical applications. To overcome the issues related to prokaryotic expression, here we report the production of recombinant hLysG2 (rhLysG2) using the methylotrophic yeast Pichia pastoris as expression host. The strong inducible alcoholoxidase 1 (AOX1) promoter was used to drive expression of the optimized hLysG2 gene. Under the optimal expression conditions, the lytic activity of rhLysG2 reached 113 U/mL of culture supernatant in shake flask cultivation and this was increased to 2084 U/mL in fed-batch fermentation. Using chitin affinity chromatography and size-exclusion chromatography, rhLysG2 was produced with a yield of 137 mg/L, purity of > 99%, molecular weight of 21,504.6 Da, and specific activity of 13,500 U/mg. In vitro assays indicated that rhLysG2 possessed muramidase activity, isopeptidase activity, and free radical scavenging activity. This report describes an efficient strategy for the production of biologically active rhLysG2 in P. pastoris on a large scale with a high yield, which provides a solid foundation for possible future pharmaceutical applications.

LYG1 exerts antitumor function through promoting the activation, proliferation, and function of CD4+ T cells

Identification of novel stimulatory cytokines with antitumor function would have great value in tumor immunotherapy investigations. Here, we report LYG1 (Lysozyme G-like 1) identified through the strategy of Immunogenomics as a novel classical secretory protein with tumor-inhibiting function. LYG1 recombinant protein (rhLYG1) could significantly suppress the growth of B16 tumors in WT B6 mice, but not in SCID-beige mice, Rag1^-/- mice, CD4⁺- or CD8⁺ T cell-deleted mice. It could increase the number of CD4⁺ and CD8⁺ T cells in tumor-infiltrating lymphocytes, tumor-draining lymph nodes, and spleens, and promote IFNγ production by T cells in tumor-bearing mice. In vitro experiments demonstrated that rhLYG1 could directly enhance IFNγ secretion by CD4⁺ T cells, but not CD8⁺ T cells. Moreover, it could promote the activation, proliferation, and IFNγ production of tumor antigen-specific CD4⁺ T cells. The tumor-inhibiting effect of LYG1 was eliminated in Ifng^-/- mice. Furthermore, LYG1 deficiency accelerated B16 and LLC1 tumor growth and inhibited the function of T cells. In summary, our findings reveal a tumor-inhibiting role for LYG1 through promoting the activation, proliferation, and function of CD4⁺ T cells in antitumor immune responses, offering implications for novel tumor immunotherapy.

Multiple specialised goose-type lysozymes potentially compensate for an exceptional lack of chicken-type lysozymes in Atlantic cod

Previous analyses of the Atlantic cod genome showed unique combinations of lacking and expanded number of genes for the immune system. The present study examined lysozyme activity, lysozyme gene distribution and expression in cod. Enzymatic assays employing specific bacterial lysozyme inhibitors provided evidence for presence of g-type, but unexpectedly not for c-type lysozyme activity. Database homology searches failed to identify any c-type lysozyme gene in the cod genome or in expressed sequence tags from cod. In contrast, we identified four g-type lysozyme genes (LygF1a-d) constitutively expressed, although differentially, in all cod organs examined. The active site glutamate residue is replaced by alanine in LygF1a, thus making it enzymatic inactive, while LygF1d was found in two active site variants carrying alanine or glutamate, respectively. In vitro and in vivo infection by the intracellular bacterium Francisella noatunensis gave a significantly reduced LygF1a and b expression but increased expression of the LygF1c and d genes as did also the interferon gamma (IFNγ) cytokine. These results demonstrate a lack of c-type lysozyme that is unprecedented among vertebrates. Our results further indicate that serial gene duplications have produced multiple differentially regulated cod g-type lysozymes with specialised functions potentially compensating for the lack of c-type lysozymes.

A novel antimicrobial peptide derived from fish goose type lysozyme disrupts the membrane of Salmonella enterica

In aquaculture, accumulation of antibiotics resulted in development of resistance among bacterial pathogens. Consequently, it became mandatory to find alternative to synthetic antibiotics. Antimicrobial peptides (AMPs) which are described as evolutionary ancient weapons have been considered as promising alternates in recent years. In this study, a novel antimicrobial peptide had been derived from goose type lysozyme (LyzG) which was identified from the cDNA library of freshwater fish Channa striatus (Cs). The identified lysozyme cDNA contains 585 nucleotides which encodes a protein of 194 amino acids. CsLyzG was closely related to Siniperca chuatsi with 92.8% homology. The depicted protein sequence contained a GEWL domain with conserved GLMQ motif, 7 active residues and 2 catalytic residues. Gene expression analysis revealed that CsLyzG was distributed in major immune organs with highest expression in head kidney. Results of temporal expression analysis after bacterial (Aeromonas hydrophila) and fungal (Aphanomyces invadans) challenges indicated a stimulant-dependent expression pattern of CsLyzG. Two antimicrobial peptides IK12 and TS10 were identified from CsLyzG and synthesized. Antibiogram showed that IK12 was active against Salmonella enterica, a major multi-drug resistant (MDR) bacterial pathogen which produces beta lactamase. The IK12 induced loss of cell viability in the bacterial pathogen. Flow cytometry assay revealed that IK12 disrupt the membrane of S. enterica which is confirmed by scanning electron microscope (SEM) analysis that reveals blebs around the bacterial cell membrane. Conclusively, CsLyzG is a potential innate immune component and the identified antimicrobial peptide has great caliber to be used as an ecofriendly antibacterial substance in aquaculture.

FMiR: A Curated Resource of Mitochondrial DNA Information for Fish

Mitochondrial genome sequences have been widely used for evolutionary and phylogenetic studies. Among vertebrates, fish are an important, diverse group, and their mitogenome sequences are growing rapidly in public repositories. To facilitate mitochondrial genome analysis and to explore the valuable genetic information, we developed the Fish Mitogenome Resource (FMiR) database to provide a workbench for mitogenome annotation, species identification and microsatellite marker mining. The microsatellites are also known as simple sequence repeats (SSRs) and used as molecular markers in studies on population genetics, gene duplication and marker assisted selection. Here, easy-to-use tools have been implemented for mining SSRs and for designing primers to identify species/habitat specific markers. In addition, FMiR can analyze complete or partial mitochondrial genome sequence to identify species and to deduce relational distances among sequences across species. The database presently contains curated mitochondrial genomes from 1302 fish species belonging to 297 families and 47 orders reported from saltwater and freshwater ecosystems. In addition, the database covers information on fish species such as conservation status, ecosystem, family, distribution and occurrence downloaded from the FishBase and IUCN Red List databases. Those fish information have been used to browse mitogenome information for the species belonging to a particular category. The database is scalable in terms of content and inclusion of other analytical modules. The FMiR is running under Linux operating platform on high performance server accessible at URL http://mail.nbfgr.res.in/fmir.

Evolution of the Vertebrate Resistin Gene Family

Resistin (encoded by Retn) was previously identified in rodents as a hormone associated with diabetes; however human resistin is instead linked to inflammation. Resistin is a member of a small gene family that includes the resistin-like peptides (encoded by Retnl genes) in mammals. Genomic searches of available genome sequences of diverse vertebrates and phylogenetic analyses were conducted to determine the size and origin of the resistin-like gene family. Genes encoding peptides similar to resistin were found in Mammalia, Sauria, Amphibia, and Actinistia (coelacanth, a lobe-finned fish), but not in Aves or fish from Actinopterygii, Chondrichthyes, or Agnatha. Retnl originated by duplication and transposition from Retn on the early mammalian lineage after divergence of the platypus, but before the placental and marsupial mammal divergence. The resistin-like gene family illustrates an instance where the locus of origin of duplicated genes can be identified, with Retn continuing to reside at this location. Mammalian species typically have a single copy Retn gene, but are much more variable in their numbers of Retnl genes, ranging from 0 to 9. Since Retn is located at the locus of origin, thus likely retained the ancestral expression pattern, largely maintained its copy number, and did not display accelerated evolution, we suggest that it is more likely to have maintained an ancestral function, while Retnl, which transposed to a new location, displays accelerated evolution, and shows greater variability in gene number, including gene loss, likely evolved new, but potentially lineage-specific, functions.

Two c-type lysozymes boost the innate immune system of the invasive ladybird Harmonia axyridis

The invasive ladybird beetle Harmonia axyridis has a two-layered immune system, featuring the constitutive production of the low-molecular-mass antimicrobial compound harmonine and the inducible production of a broad range of antimicrobial peptides (AMPs). Here we show that the immune system also features two c-type lysozymes, the acidic c-lys3 (pI = 5.46) and the basic c-lys4 (pI = 8.18). The injection of bacteria into H.axyridis boosted c-lys4 gene expression 8-fold in the gut, whereas the c-lys3 gene was expressed at comparable levels in both naïve and challenged beetles. Both c-lys3 and c-lys4 were expressed in Pichia pastoris and the bacteriolytic activity of the recombinant proteins was found to be calcium-dependent with pH maxima of 6.0 and 6.5, respectively. In a Bacillus subtilis growth inhibition assay, the antimicrobial activity of harmonine and two highly-inducible H.axyridis AMPs (coleoptericins) was potentiated in the presence of c-lys4 but not c-lys3, resulting in 4-fold (harmonine) and up to 16-fold (AMP) lower minimum inhibitory concentrations. Our results suggest that two structurally and functionally distinct lysozymes contribute to innate immune responses of H.axyridis and augment the harmonine and AMP components of the immune response.

Evolution of the vertebrate goose-type lysozyme gene family

BACKGROUND

Lysozyme g is an antibacterial enzyme that was first found in the eggs of some birds, but recently has been found in additional species, including non-vertebrates. Some previously characterized lysozyme g sequences are suggested to have altered secretion potential and enzymatic activity, however the distribution of these altered sequences is unknown. Duplicated copies of the lysozyme g gene exist in some species; however, the origins of the duplicates and their roles in altered function are unclear.

RESULTS

We identified 234 lysozyme g sequences from 118 vertebrate species, including 181 sequences that are full or near full length representing all vertebrate classes except cartilaginous fish. Phylogenetic analysis shows that most lysozyme g gene duplicates are recent or lineage specific events, however three amplification events are more ancient, those in an early amniote, an early mammal, and an early teleost. The older gene duplications are associated with changes in function, including changes in secretion potential and muramidase antibacterial enzymatic activity.

CONCLUSIONS

Lysozyme g is an essential muramidase enzyme that is widespread in vertebrates. Duplication of the lysozyme g gene, and the retention of non-secreted isozymes that have lost enzymatic activity indicate that lysozyme g has an activity other than the muramidase activity associated with being an antibacterial enzyme.