Cloning and expression of a novel gene encoding a new antibacterial peptide from silkworm, Bombyx mori

Diversity of Antimicrobial Peptides in Silkworm

Antimicrobial resistance is a phenomenon that the present-day world is witnessing that poses a serious threat to global health. The decline in the development of novel therapeutics over the last couple of decades has exacerbated the situation further. In this scenario, the pursuit of new alternative therapeutics to commonly used antibiotics has gained predominance amongst researchers across the world. Antimicrobial peptides (AMPs) from natural sources have drawn significant interest in the recent years as promising pharmacological substitutes over the conventional antibiotics. The most notable advantage of AMPs is that microorganisms cannot develop resistance to them. Insects represent one of the potential sources of AMPs, which are synthesized as part of an innate immune defence against invading pathogens. AMPs from different insects have been extensively studied, and silkworm is one of them. Diverse classes of AMPs (including attacins, cecropins, defensins, enbocins, gloverins, lebocins and moricins) were identified from silkworm that exhibit antimicrobial property against bacteria, fungi and viruses, indicating their potential therapeutic benefits. This review briefs about the immune responses of silkworm to invading pathogens, the isolation of AMPs from silkworms, AMPs reported in silkworms and their activity against various microorganisms.

Zinc supplementation modifies brain tissue transcriptome of Apis mellifera honeybees

BACKGROUND

Bees are the most important group of pollinators worldwide and their populations are declining. In natural conditions, Apis mellifera depends exclusively on food from the field to meet its physiological demands. In the period of scarcity, available resources are insufficient and artificial supplementation becomes essential for maintaining the levels of vitamins, proteins, carbohydrates, and minerals of colonies. Among these minerals, zinc is essential in all living systems, particularly for the regulation of cell division and protein synthesis, and is a component of more than 200 metalloenzymes.

RESULTS

The total RNA extracted from the brain tissue of nurse bees exposed to different sources and concentrations of zinc was sequenced. A total of 1,172 genes in the treatment that received an inorganic source of zinc and 502 genes that received an organic source of zinc were found to be differentially expressed among the control group. Gene ontology enrichment showed that zinc can modulate important biological processes such as nutrient metabolism and the molting process.

CONCLUSIONS

Our results indicate that zinc supplementation modulates the expression of many differentially expressed genes and plays an important role in the development of Apis mellifera bees. All the information obtained in this study can contribute to future research in the field of bee nutrigenomics.

Label-free LC-MS/MS proteomic analysis of the hemolymph of silkworm larvae infected with Beauveria bassiana

Beauveria bassiana, a pathogen of the economically important silkworm (Bombyx mori), causes serious losses in the sericulture industry; however, the mechanisms underlying B. bassiana infection and the silkworm response are not fully understood. To obtain new insights into the interaction between B. bassiana and its host, hemolymph samples from fifth instar silkworm larvae infected with B. bassiana were analyzed at 36-h post-inoculation using a label-free LC-MS/MS proteomic technique. In total, 671 proteins were identified in the hemolymph, including 87 differentially expressed proteins, 42 up-regulated and 45 down-regulated in infected larvae. Six were detected only in infected larvae, and five were detected only in uninfected larvae. Based on GO annotations, 48 of the differentially expressed proteins were involved in molecular functions, 42 were involved in biological processes, and 39 were involved in cell components. A KEGG pathway analysis indicated that these differentially expressed proteins participate in 85 signal transduction pathways, including the amoebiasis, MAPK signaling, Hippo signaling, Toll and Imd signaling, and lysosome pathways. The silkworm hemolymph is the main site for B. bassiana replication. We identified differentially expressed proteins involved in the regulation of the host response to B. bassiana infection, providing important experimental data for the identification of key factors contributing to the interaction between the pathogenic fungus and its host.

Comparative Analysis of the Integument Transcriptomes between Stick Mutant and Wild-Type Silkworms

In insects, the integument provides mechanical support for the whole body and protects them from infections, physical and chemical injuries, and dehydration. Diversity in integument properties is often related to body shape, behavior, and survival rate. The stick (sk) silkworm is a spontaneous mutant with a stick-like larval body that is firm to the touch and, thus, less flexible. Analysis of the mechanical properties of the cuticles at day 3 of the fifth instar (L5D3) of sk larvae revealed higher storage modulus and lower loss tangent. Transcriptome sequencing identified a total of 19,969 transcripts that were expressed between wild-type Dazao and the sk mutant at L5D2, of which 11,596 transcripts were novel and detected in the integument. Differential expression analyses identified 710 upregulated genes and 1009 downregulated genes in the sk mutant. Gene Ontology (GO) enrichment analysis indicated that four chitin-binding peritrophin A domain genes and a chitinase gene were upregulated, whereas another four chitin-binding peritrophin A domain genes, a trehalase, and nine antimicrobial peptides were downregulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that two functional pathways, namely, fructose and mannose metabolism and tyrosine metabolism, were significantly enriched with differentially-expressed transcripts. This study provides a foundation for understanding the molecular mechanisms underlying the development of the stiff exoskeleton in the sk mutant.

Molecular Cloning, Bioinformatic Analysis, and Expression of Bombyx mori Lebocin 5 Gene Related to Beauveria bassiana Infection

A full-length cDNA of lebocin 5 (BmLeb5) was first cloned from silkworm, Bombyx mori, by rapid amplification of cDNA ends. The BmLeb5 gene is 808 bp in length and the open reading frame encodes a 179-amino acid hydroxyproline-rich peptide. Bioinformatic analysis results showed that BmLeb5 owns an O-glycosylation site and four RXXR motifs as other lebocins. Sequence similarity and phylogenic analysis results indicated that lebocins form a multiple gene family in silkworm as cecropins. Quantitative real-time PCR analysis revealed that BmLeb5 was highest expressed in the fat body. In the silkworm larvae infected by Beauveria bassiana, the expression level of BmLeb5 was upregulated in the fat body and hemolymph which are the most important immune tissues in silkworm. The recombinant protein of BmLeb5 was for the first time successfully expressed with prokaryotic expression system and purified. There are no reports so far that the expression of lebocins could be induced by entomopathogenic fungus. Our study suggested that BmLeb5 might play an important role in the immune response of silkworm to defend B. bassiana infection. The results also provided helpful information for further studying the lebocin family functioned in antifungal immune response in the silkworm.

Nonfunctional ingestion of plant miRNAs in silkworm revealed by digital droplet PCR and transcriptome analysis

Since a plant miRNA (miR168) cross-regulating a mammalian transcript was reported, miRNA-mediated cross-kingdom communication has become one of the most compelling but controversial topics. In the present study, we used silkworm and mulberry, which is a model for studies on the interactions between the insect and its host plant, to address whether miRNA-mediated cross-kingdom communication is a common phenomenon. The results of TA clone, Sanger sequencing and droplet digital PCR demonstrated that several mulberry-derived miRNAs could enter to silkworm hemolymph and multiple tested tissues. Synthetic miR166b was also detected in hemolymph and fat body. However, the ingestion of synthetic miR166b did not play roles in silkworm physiological progress, which was revealed by RNA-seq analyses, RT-PCR, and phenotypic investigations. Mulberry miRNAs are convincingly transferred to the silkworm orally and no physiological process associated with the miRNAs was demonstrable. The results provided a new aspect of cross-kingdom miRNA transfer.

The InhA metalloproteases of Bacillus cereus contribute concomitantly to virulence

The virulence of Bacillus cereus requires that bacteria have the capacity to colonize their host, degrade specific tissues, and circumvent the host immune system. To study this aspect of pathogenesis, we focused on three metalloproteases, InhA1, InhA2, and InhA3, which share more than 66% identity. The expression of these metalloprotease genes was assessed by transcriptional fusions with a lacZ reporter gene. The expression profiles suggest a complementary time course of InhA production. Indeed, the genes are simultaneously expressed but are oppositely controlled during stationary phase. We constructed single and multiple inhA mutants and assessed the bacterial locations of the proteins as well as their individual or additive roles in macrophage escape and toxicity, antibacterial-peptide cleavage, and virulence. InhA1, a major component of the spore exosporium, is the only InhA metalloprotease involved in bacterial escape from macrophages. A mutant lacking inhA1, inhA2, and inhA3 shows a strong decrease in the level of virulence for insects. Taken together, these results show that the InhA metalloproteases of B. cereus are important virulence factors that may allow the bacteria to counteract the host immune system.

Expression of antimicrobial peptide genes encoding Enbocin and Gloverin isoforms in the silkworm, Bombyx mori

Antimicrobial peptides, Enbocin and Gloverin isoforms from the silkworm Bombyx mori, were analyzed for expression of these peptide genes. Tissue-specific expression of Enbocin and Bmgloverin isoform genes was observed mainly in the fat body upon injection of Escherichia coli. Peptidoglycan and lipopolysaccharide triggered expression of these genes in vivo. On the other hand, lipid A activated Bmgloverin isoform genes but not Enbocin isoform genes. These results illustrate the fact that expression of Enbocin and Bmgloverin isoform genes is inducible by bacteria and that the effects of bacterial cell wall components on the activation of these peptide genes are not necessarily the same. In addition, selective activation of the Enbocin2, Bmgloverin2, and Bmgloverin4 genes by BmRelB rather than BmRelA was observed, providing additional evidence for the occurrence of selective activation of antimicrobial peptide genes by a Rel protein. These results suggest complex regulatory mechanisms in insect antimicrobial peptide genes by bacterial cell wall components.

Structures, regulatory regions, and inductive expression patterns of antimicrobial peptide genes in the silkworm Bombyx mori

Antimicrobial peptides (AMPs) are a group of immune proteins that protect the host from infection. In Drosophila, seven groups of inducible AMPs have been identified, with activities against fungi and gram-positive and gram-negative bacteria. On the basis of the silkworm genome sequence and expressed sequence tags, we identified 35 AMP genes, mostly belonging to the cecropin, moricin, and gloverin gene families. We predicted the core promoters required for gene transcription and the cis-regulatory elements for NF-kappaB/Rel and GATA transcription factors. The expression profiles of these genes after an immune challenge with lipopolysaccharide were examined by reverse transcription PCR. Members of the cecropin B and gloverin A subfamilies were intensely expressed in the fat body after induction. In contrast, those of the moricin B subfamily were not expressed under the same conditions. Such results suggest that these regulatory elements and their positions in the upstream regions play an important role in regulating the transcription of these defense genes.

Purification and cDNA cloning of a cecropin from the longicorn beetle, Acalolepta luxuriosa

We have cloned and characterized a novel antibacterial peptide from the hemolymph of the coleopteran insect Acalolepta luxuriosa, of the superfamily Cerambyocidea. This peptide is active against Micrococcus luteus and Escherichia coli, and the amino acid sequence deduced by cloning of the cDNA identifies it as a coleopteran cecropin. Sequence comparisons and phylogenetic analyses performed using Clustal X suggest that this cecropin is evolutionarily intermediate between dipteran and lepidopteran cecropins. The results of MALDI-TOF mass spectrometry indicate that the mature form of this antibacterial peptide is 35 amino acid residues in length and has an amidated C-terminal isoleucine. This report is the first description of a cecropin from a coleopteran insect.

Trichuris suis: detection of antibacterial activity in excretory-secretory products from adults

Antibacterial activity was detected in excretory-secretory products (ESP) of adult Trichuris suis cultured in vitro in serum-free media. Gram-negative bacteria (Campylobacter jejuni, Campylobacter coli, and Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) were sensitive to ESP. Susceptibility was dependent on the concentration of ESP but not on the inoculum size. Preliminary assessment of the mode of action suggests a bacteriocidal mechanism. This antibacterial activity was heat stable and resistant to digestion with pronase E and trypsin. Based on ultrafiltration experiments, the activity is less than 10,000 MW. This excreted/secreted antibacterial activity from T. suis is likely a component of a humoral defense system for this helminth.

Purification and characterization of three antifungal proteins from cheeseweed (Malva parviflora)

Three potent antimicrobial proteins were purified from cheeseweed (Malva parviflora) seeds. These antimicrobial proteins, named CW-3, CW-4, and CW-5, showed different antimicrobial spectrum and potency compared to the two heterologous antimicrobial proteins (CW-1 and CW-2) purified previously. CW-3 and CW-4 possess antimicrobial activities against Phytophthora infestans (Pi), but not Fusarium graminearum (Fg). A database search indicated that CW-3 shares high homology to cotton vicilin, an abundant seed storage protein. CW-4 shares homology to 2S albumin, another seed storage protein from cotton. CW-5 has antimicrobial activity against Fg, but no activity against Pi was observed at protein concentration up to 50 ppm. Under low salt condition, CW-5 showed potent antimicrobial activity against Fg, but under high salt condition, the antimicrobial activity was drastically diminished. Database search indicated that CW-5 has high homology to a lipid transfer protein from grape. The IC(50) values of the three purified antimicrobial proteins under both low and high salt conditions were determined. The isolation of five antimicrobial proteins for the first time from a single plant source provides further understanding of the plant innate defense system and insight on how plants evolve their complex and complementary antimicrobial system that is important in the early stage of development.

Amphipathic, alpha-helical antimicrobial peptides

Gene-encoded antimicrobial peptides are an important component of host defense in animals ranging from insects to mammals. They do not target specific molecular receptors on the microbial surface, but rather assume amphipathic structures that allow them to interact directly with microbial membranes, which they can rapidly permeabilize. They are thus perceived to be one promising solution to the growing problem of microbial resistance to conventional antibiotics. A particularly abundant and widespread class of antimicrobial peptides are those with amphipathic, alpha-helical domains. Due to their relatively small size and synthetic accessibility, these peptides have been extensively studied and have generated a substantial amount of structure-activity relationship (SAR) data. In this review, alpha-helical antimicrobial peptides are considered from the point of view of six interrelated structural and physicochemical parameters that modulate their activity and specificity: sequence, size, structuring, charge, amphipathicity, and hydrophobicity. It begins by providing an overview of how these vary in peptides from different natural sources. It then analyzes how they relate to the currently accepted model for the mode of action of alpha-helical peptides, and discusses what the numerous SAR studies that have been carried out on these compounds and their analogues can tell us. A comparative analysis of the many alpha-helical, antimicrobial peptide sequences that are now available then provides further information on how these parameters are distributed and interrelated. Finally, the systematic variation of parameters in short model peptides is used to throw light on their role in antimicrobial potency and specificity. The review concludes with some considerations on the potentials and limitations for the development of alpha-helical, antimicrobial peptides as antiinfective agents.

Animal antimicrobial peptides: an overview

Antibiotic peptides are a key component of the innate immune systems of most multicellular organisms. Despite broad divergences in sequence and taxonomy, most antibiotic peptides share a common mechanism of action, i.e., membrane permeabilization of the pathogen. This review provides a general introduction to the subject, with emphasis on aspects such as structural types, post-translational modifications, mode of action or mechanisms of resistance. Some of these questions are treated in depth in other reviews in this issue. The review also discusses the role of antimicrobial peptides in nature, including several pathological conditions, as well as recent accounts of their application at the preclinical level.

Molecular cloning and characterization of a cDNA encoding a transferrin homolog from Bombyx mori

We isolated a cDNA representing a message that was strongly induced by injection with E. coli in Bombyx mori. The 2160 bp cDNA has an open reading frame of 644 amino acids and the deduced product a predicted molecular mass of 71 kDa. The cDNA sequence shared high homology with the transferrins known so far, and its deduced peptide had unique features of transferrins, that is, sites of cystein residues and iron binding. We suggest that the B. mori transferrin plays an important role in the self-defense system.