Serpin-1a and serpin-6 regulate the Toll pathway immune homeostasis by synergistically inhibiting the Spätzle-processing enzyme CLIP2 in silkworm, Bombyx mori.

The Toll receptor signaling pathway is an important innate immune response of insects to pathogen infection; its extracellular signal transduction involves serine protease cascade activation. However, excessive or constitutive activation of the Toll pathway can be detrimental. Hence, the balance between activation and inhibition of the extracellular protease cascade must be tightly regulated to achieve favorable outcomes. Previous studies have shown that serpins-serine protease inhibitors-negatively regulate insect innate immunity by inhibiting extracellular protease cascade signaling. Although the roles of serpins in insect innate immunity are well described, the physiological mechanisms underlying their synergistic effects remain poorly understand. Here, we characterize the molecular mechanism by which serpin-1a and serpin-6 synergistically maintain immune homeostasis of the silkworm Toll pathway under physiological and pathological conditions. Through in vitro biochemical assays and in vivo bioassays, we demonstrate that clip-domain serine protease 2 (CLIP2), as the Toll cascade-activating terminal protease, is responsible for processing proSpätzle1 to induce the expression of antimicrobial peptides. Further biochemical and genetic analyses indicate that constitutively expressed serpin-1a and inducible serpin-6 synergistically target CLIP2 to maintain homeostasis of the silkworm Toll pathway under physiological and pathological conditions. Taken together, this study provides new insights into the precise regulation of Toll cascade activation signals in insect innate immune responses and highlights the importance and complexity of insect immune homeostasis regulation.

Structural Characterization and Functional Analysis of Mevalonate Kinase from Tribolium castaneum (Red Flour Beetle).

Mevalonate kinase (MevK) is an important enzyme in the mevalonate pathway that catalyzes the phosphorylation of mevalonate into phosphomevalonate and is involved in juvenile hormone biosynthesis. Herein, we present a structure model of MevK from the red flour beetle Tribolium castaneum (TcMevK), which adopts a compact α/ß conformation that can be divided into two parts: an N-terminal domain and a C-terminal domain. A narrow, deep cavity accommodating the substrate and cofactor was observed at the junction between the two domains of TcMevK. Computational simulation combined with site-directed mutagenesis and biochemical analyses allowed us to define the binding mode of TcMevK to cofactors and substrates. Moreover, TcMevK showed optimal enzyme activity at pH 8.0 and an optimal temperature of 40 °C for mevalonate as the substrate. The expression profiles and RNA interference of TcMevK indicated its critical role in controlling juvenile hormone biosynthesis, as well as its participation in the production of other terpenoids in T. castaneum. These findings improve our understanding of the structural and biochemical features of insect Mevk and provide a structural basis for the design of MevK inhibitors.

Structural basis for juvenile hormone biosynthesis by the juvenile hormone acid methyltransferase.

Juvenile hormone (JH) acid methyltransferase (JHAMT) is a rate-limiting enzyme that converts JH acids or inactive precursors of JHs to active JHs at the final step of JH biosynthesis in insects and thus presents an excellent target for the development of insect growth regulators or insecticides. However, the three-dimensional properties and catalytic mechanism of this enzyme are not known. Herein, we report the crystal structure of the JHAMT apoenzyme, the three-dimensional holoprotein in binary complex with its cofactor S-adenosyl-l-homocysteine, and the ternary complex with S-adenosyl-l-homocysteine and its substrate methyl farnesoate. These structures reveal the ultrafine definition of the binding patterns for JHAMT with its substrate/cofactor. Comparative structural analyses led to novel findings concerning the structural specificity of the progressive conformational changes required for binding interactions that are induced in the presence of cofactor and substrate. Importantly, structural and biochemical analyses enabled identification of one strictly conserved catalytic Gln/His pair within JHAMTs required for catalysis and further provide a molecular basis for substrate recognition and the catalytic mechanism of JHAMTs. These findings lay the foundation for the mechanistic understanding of JH biosynthesis by JHAMTs and provide a rational framework for the discovery and development of specific JHAMT inhibitors as insect growth regulators or insecticides.

Antibacterial Mechanism of Gloverin2 from Silkworm, Bombyx mori.

Gloverin is one of the glycine-rich antimicrobial peptide exclusively found in Lepidoptera insects. It is generally activated through the innate immune system in insects. In this study, recombinant Gloverin2 from Bombyx mori (BmGlv2) was synthesized using a prokaryotic expression system. Circular dichroism spectroscopy showed that the recombinant BmGlv2 has random coil structure, which is relatively stable at the temperatures ranging from 15 to 82.5 °C. Antimicrobial activity analysis revealed that BmGlv2 significantly inhibited the growth of gram-negative bacteria, Escherichia coli JM109 and Pseudomonas putida, by disrupting cell integrity. Western blotting and immunofluorescence analyses suggested that BmGlv2 absorbed on the cell surface after incubation, which might be the first step in the antibacterial process. Our results also proved that the cell wall component lipopolysaccharides (LPS) induce a conformational change in BmGlv2 from a random coil to α-helix. Subsequently, α-helical BmGlv2 would recruit more BmGlv2 and form higher aggregation state. Collectively, these findings expand our understanding of antibacterial mechanism of BmGlv2.

Proteomics Provides Insight into the Interaction between Mulberry and Silkworm.

Mulberry leaves have been selected as a food source for the silkworm (Bombyx mori) for over 5000 years. However, the interaction mechanisms of mulberry-silkworm remain largely unknown. We explore the interaction between mulberry and silkworm at the protein level. Total proteins were extracted from mulberry leaves and silkworm feces on day 5 of the fifth larval instar and analyzed on shotgun liquid chromatography-tandem mass spectrometry, respectively. In total, 2076 and 210 foliar proteins were identified from mulberry leaves and silkworm feces, respectively. These proteins were classified into four categories according to their subcellular location: chloroplast proteins, mitochondrial proteins, secretory-pathway proteins, and proteins of other locations. Chloroplast proteins accounted for 68.3% in mulberry leaves but only 23.2% in the feces. In contrast, secretory-pathway proteins had low abundance in mulberry leaves (7.3%) but were greatly enriched to the largest component in the feces (60.1%). Most of the foliar secretory-pathway proteins in the feces were found to be resistant to silkworm feeding by becoming involved in primary metabolite, proteinase inhibition, cell-wall remodeling, redox regulation, and pathogen-resistant processes. On the contrary, only six defensive proteins were identified in the fecal chloroplast proteins including two key proteins responsible for synthesizing jasmonic acid, although chloroplast proteins were the second largest component in the feces. Collectively, the comparative proteomics analyses indicate that mulberry leaves not only provide amino acids to the silkworm but also display defense against silkworm feeding, although the silkworm grows very well by feeding on mulberry leaves, which provides new insights into the interactions between host-plant and insect herbivores.

Structural insights into the cofactor-assisted substrate recognition of yeast methylglyoxal/isovaleraldehyde reductase Gre2.

Saccharomyces cerevisiae Gre2 (EC1.1.1.283) serves as a versatile enzyme that catalyzes the stereoselective reduction of a broad range of substrates including aliphatic and aromatic ketones, diketones, as well as aldehydes, using NADPH as the cofactor. Here we present the crystal structures of Gre2 from S. cerevisiae in an apo-form at 2.00Å and NADPH-complexed form at 2.40Å resolution. Gre2 forms a homodimer, each subunit of which contains an N-terminal Rossmann-fold domain and a variable C-terminal domain, which participates in substrate recognition. The induced fit upon binding to the cofactor NADPH makes the two domains shift toward each other, producing an interdomain cleft that better fits the substrate. Computational simulation combined with site-directed mutagenesis and enzymatic activity analysis enabled us to define a potential substrate-binding pocket that determines the stringent substrate stereoselectivity for catalysis.

Silk gland-specific proteinase inhibitor serpin16 from the Bombyx mori shows cysteine proteinase inhibitory activity.

Serpins (serine proteinase inhibitors) are widely distributed in different species and are well known for their inhibitory activities towards serine proteinases. Here, we report the functional characterization of Bombyx mori serpin16. Expression analysis showed that serpin16 was specifically expressed at high levels in the silk gland at both the transcriptional and translational levels. Moreover, homology modeling and multi-sequence alignment suggested that serpin16 had a canonical serpin fold, but it contained a unique reactive center loop, which was obviously shorter than that of typical serpins. Inhibitory activity analyses revealed that the target proteinase of serpin18 is a cysteine proteinase, rather than a serine proteinase. Furthermore, a Michaelis complex model of serpin16 with its target proteinase was constructed to explain the structural basis of how serpin16 recognizes the cysteine proteinase and its target specificity.

Structural Insights into the Substrate Binding of Farnesyl Diphosphate Synthase FPPS1 from Silkworm, Bombyx mori.

Farnesyl diphosphate synthase (FPPS) is an important enzyme involved in the juvenile hormone (JH) biosynthesis pathway. Herein, we report the crystal structure of a type-I Lepidopteran FPPS from Bombyx mori (BmFPPS1) at 2.80 Å resolution. BmFPPS1 adopts an α-helix structure with a deep cavity at the center of the overall structure. Computational simulations combined with biochemical analysis allowed us to define the binding mode of BmFPPS1 to its substrates. Structural comparison revealed that BmFPPS1 adopts a structural pattern similar to that of type-II FPPS but exhibits a distinct substrate-binding site. These findings provide a structural basis for understanding substrate preferences and designing FPPS inhibitors. Furthermore, the expression profiles and RNA interference of BmFPPSs indicated that they play critical roles in the JH biosynthesis and larval-pupal metamorphosis. These findings enhance our understanding of the structural features of type-I Lepidopteran FPPS while providing direct evidence for the physiological role of BmFPPSs in silkworm development.

Structural Characterization and Physiological Role of Bombyx mori Fibroinase in the Silk Gland Development.

Silkworm is a highly valuable insect that produces silk through secretion by a silk gland. Within this gland, a type of cathepsin L protease called Fibroinase was identified as an enzyme for hydrolyzing the primary components of silk, including fibroin and sericin. Here, we determined the crystal structure of Fibroinase fromBombyx mori at a resolution of 1.56 Å. Comparative structural analysis revealed that Fibroinase adopted a similar structural pattern with papain-type cathepsin, consisting of an N-terminal domain and a C-terminal domain. The interface between the domains forms a substrate-binding cleft, where the E64 inhibitor noncovalently binds in a novel manner. Additionally, computational simulations combined with biochemical analysis allowed us to define the binding mode and inhibition mechanism of physiological inhibitor Bombyx cysteine protease inhibitor (BCPI) with Fibroinase. Moreover, the expression profiles and RNA interference of Fibroinase indicated its critical role in removing silk proteins in the silk gland lumen and the destruction of silk gland tissue during the larval-pupal metamorphosis. These findings enhance our understanding of the structural and biochemical features of Fibroinase and its inhibitors, while also providing evidence for the physiological role of Fibroinase in silk gland development.

Fibroinase plays a vital role in silk gland degeneration by regulating autophagy and apoptosis in the silkworm, Bombyx mori.

The silkworm is an incredibly valuable insect that produces silk through its silk gland. Within this organ, Fibroinase has been identified and named due to its ability to fibroin degradation. The expression of Fibroinase in the silk gland significantly increases during the larval-pupal stage, which might be associated with the degeneration of the silk gland. In this study, Fibroinase was overexpressed and knocked down specifically both in the middle and posterior silk glands, respectively, using transgenic technology. The investigation of silk gland development in these transgenic silkworms showed that Fibroinase plays a direct role in accelerating silk gland degeneration. The staining analyses performed in the silk glands of transgenic silkworms suggest that Fibroinase is involved in the processes of autophagy and apoptosis during silk gland degeneration. Further experiments demonstrated that Fibroinase, acting as a lysosomal regulator, negatively regulates autophagy via the mTOR (mechanistic target of rapamycin) pathway. Moreover, during apoptosis, Fibroinase could activate Caspase3 by increasing the activity of BmCaspase1, ultimately accelerating the apoptosis process. These findings enhance our understanding of the physiological role of Fibroinase in promoting silk gland degeneration, which plays a role in breaking down proteins in the silk gland and coordinating the regulation of autophagy and apoptosis.

Structure of yeast sulfhydryl oxidase erv1 reveals electron transfer of the disulfide relay system in the mitochondrial intermembrane space.

The disulfide relay system in the mitochondrial intermembrane space drives the import of proteins with twin CX(9)C or twin CX(3)C motifs by an oxidative folding mechanism. This process requires disulfide bond transfer from oxidized Mia40 to a substrate protein. Reduced Mia40 is reoxidized/regenerated by the FAD-linked sulfhydryl oxidase Erv1 (EC 1.8.3.2). Full-length Erv1 consists of a flexible N-terminal shuttle domain (NTD) and a conserved C-terminal core domain (CTD). Here, we present crystal structures at 2.0 Å resolution of the CTD and at 3.0 Å resolution of a C30S/C133S double mutant of full-length Erv1 (Erv1FL). Similar to previous homologous structures, the CTD exists as a homodimer, with each subunit consisting of a conserved four-helix bundle that accommodates the isoalloxazine ring of FAD and an additional single-turn helix. The structure of Erv1FL enabled us to identify, for the first time, the three-dimensional structure of the Erv1NTD, which is an amphipathic helix flanked by two flexible loops. This structure also represents an intermediate state of electron transfer from the NTD to the CTD of another subunit. Comparative structural analysis revealed that the four-helix bundle of the CTD forms a wide platform for the electron donor NTD. Moreover, computational simulation combined with multiple-sequence alignment suggested that the amphipathic helix close to the shuttle redox enter is critical for the recognition of Mia40, the upstream electron donor. These findings provide structural insights into electron transfer from Mia40 via the shuttle domain of one subunit of Erv1 to the CTD of another Erv1 subunit.

Structures of Saccharomyces cerevisiae D-arabinose dehydrogenase Ara1 and its complex with NADPH: implications for cofactor-assisted substrate recognition.

The primary role of yeast Ara1, previously mis-annotated as a D-arabinose dehydrogenase, is to catalyze the reduction of a variety of toxic α,ß-dicarbonyl compounds using NADPH as a cofactor at physiological pH levels. Here, crystal structures of Ara1 in apo and NADPH-complexed forms are presented at 2.10 and 2.00 Šresolution, respectively. Ara1 exists as a homodimer, each subunit of which adopts an (α/ß)8-barrel structure and has a highly conserved cofactor-binding pocket. Structural comparison revealed that induced fit upon NADPH binding yielded an intact active-site pocket that recognizes the substrate. Moreover, the crystal structures combined with computational simulation defined an open substrate-binding site to accommodate various substrates that possess a dicarbonyl group.

Structural plasticity of the thioredoxin recognition site of yeast methionine S-sulfoxide reductase Mxr1.

The methionine S-sulfoxide reductase MsrA catalyzes the reduction of methionine sulfoxide, a ubiquitous reaction depending on the thioredoxin system. To investigate interactions between MsrA and thioredoxin (Trx), we determined the crystal structures of yeast MsrA/Mxr1 in their reduced, oxidized, and Trx2-complexed forms, at 2.03, 1.90, and 2.70 Å, respectively. Comparative structure analysis revealed significant conformational changes of the three loops, which form a plastic "cushion" to harbor the electron donor Trx2. The flexible C-terminal loop enabled Mxr1 to access the methionine sulfoxide on various protein substrates. Moreover, the plasticity of the Trx binding site on Mxr1 provides structural insights into the recognition of diverse substrates by a universal catalytic motif of Trx.

Clinical effectiveness of a pneumatic compression device combined with low-molecular-weight heparin for the prevention of deep vein thrombosis in trauma patients: A single-center retrospective cohort study.

BACKGROUND: To investigate the clinical effectiveness of a pneumatic compression device (PCD) combined with low-molecular-weight heparin (LMWH) for the prevention and treatment of deep vein thrombosis (DVT) in trauma patients. METHODS: This study retrospectively analyzed 286 patients with mild craniocerebral injury and clavicular fractures admitted to our department from January 2016 to February 2020. Patients treated with only LMWH served as the control group, and patients treated with a PCD combined with LMWH as the observation group. The incidence of DVT, postoperative changes in the visual analogue scale (VAS) score, and coagulation function were observed and compared between the two groups. Excluding the influence of other single factors, binary logistic regression analysis was used to evaluate the use of a PCD in the patient's postoperative coagulation function. RESULTS: After excluding 34 patients who did not meet the inclusion criteria, 252 patients were were included. The incidence of DVT in the observation group was significantly lower than that in the control group (5.6% vs. 15.1%, χ2=4.605, P<0.05). The postoperative VAS scores of the two groups were lower than those before surgery (P<0.05). The coagulation function of the observation group was significantly higher than that of the control group, with a better combined anticoagulant effect (P<0.05). There were no significant differences between the two groups in preoperative or postoperative Glasgow Coma Scale scores, intraoperative blood loss, postoperative infection rate, or length of hospital stay (P>0.05). According to logistic regression analysis, the postoperative risk of DVT in patients who received LMWH alone was 1.764 times that of patients who received LMWH+PCD (P<0.05). The area under the receiver operating characteristic (AUROC) curve of partial thromboplastin time (APTT) and platelet (PLT) were greater than 0.5, indicating that they were the influence indicators of adding PCD to prevent DVT. Excluding the influence of other variables, LMWH+PCD effectively improved the coagulation function of patients. CONCLUSIONS: Compared with LMWH alone, LMWH+PCD could improve blood rheology and coagulation function in patients with traumatic brain injury and clavicular fracture, reduce the incidence of DVT, shorten the length of hospital stay, and improve the clinical effectiveness of treatment.

Structural characterization and functional analysis of juvenile hormone acid methyltransferase JHAMT3 from the silkworm, Bombyx mori.

Juvenile hormone acid methyltransferase (JHAMT) is a rate-limiting enzyme of juvenile hormone (JH) biosynthesis in insects. It transfers the methyl group of S-adenosyl methionine to either the carboxyl group of JH acids or farnesoic acid to produce JH. Six JHAMT paralogues have been identified in the silkworm (Bombyx mori); among them, JHAMT1 and JHAMT2 display a methyltransferase activity. Here, the three-dimensional crystal structure of inactive JHAMT3 and the binary complex of JHAMT3 with its cofactor S-adenosyl-l-homocysteine were determined through X-ray crystallization. Comparative structural analysis revealed that JHAMT3 adopted a similar structural pattern to that of functional JHAMT2, which comprised one core Rossmann fold domain and one substrate-binding domain. Similar to JHAMT2, JHAMT3 underwent a conformational change at the Rossmann fold domain because of cofactor binding, which promoted ligand accommodation. However, it exhibited a relatively rigid substrate-binding pocket compared with that of JHAMT2. JHAMT3 was also highly expressed in the silk gland of fourth- and fifth-instar B. mori larvae. The results of expression profiling combined with activity analysis suggested that JHAMT3 might function as a binding protein of JH acids for the regulation of JH acid titers. These findings provide a structural basis for enhancing the understanding of the physiological function of JHAMT3 and a rational framework for the development of potent and specific inhibitors of JHAMT family members.

Structural insights into the substrate binding of phosphomevalonate kinase from the silkworm, Bombyx mori.

Phosphomevalonate kinase (PMK) is an important enzyme involved in the juvenile hormone (JH) biosynthesis pathway that catalyzes the phosphorylation of mevalonate 5-phosphate into mevalonate 5-diphosphate in the mevalonate pathway. Herein, we report the crystal structure of insect PMK from Bombyx mori (BmPMK) at a resolution of 1.60 Å. The overall structure of BmPMK adopts a compact α/ß conformation with two parts: the core and lid regions. The interface between the core and lid regions forms a continuous and negatively charged groove to accommodate the substrates. Using computational simulation combined with site-directed mutagenesis and biochemical analysis, we define the binding mode of BmPMK with the cofactor and the substrate, which provides a structural basis for understanding the catalytic mechanism and the design of inhibitors of PMK. Moreover, BmPMK showed the optimal enzyme activity at pH 8.0, and the optimal temperature was 30 °C, using mevalonate 5-phosphate as the substrate. The expression profiles and kinetic analyses of BmPMK indicated that it plays critical role in the control of JH biosynthesis in silkworms. Collectively, these findings provide a better understanding of the structural and biochemical features of insect PMK.

Structural insights into the cofactor-assisted substrate recognition of yeast quinone oxidoreductase Zta1.

Quinone oxidoreductase (QOR EC1.6.5.5) catalyzes the reduction of quinone to hydroxyquinone using NADPH as a cofactor. Here we present the crystal structure of the ζ-crystallin-like QOR Zta1 from Saccharomycescerevisiae in apo-form at 2.00 Šand complexed with NADPH at 1.59 Šresolution. Zta1 forms a homodimer, with each subunit containing a catalytic and a cofactor-binding domain. Upon NADPH binding to the interdomain cleft, the two domains shift towards each other, producing a better fit for NADPH, and tightening substrate binding. Computational simulation combined with site-directed mutagenesis and enzymatic activity analysis defined a potential quinone-binding site that determines the stringent substrate specificity. Moreover, multiple-sequence alignment and kinetics assays implied that a single-residue change from Arg in lower organisms to Gly in vertebrates possibly resulted in elevation of enzymatic activity of ζ-crystallin-like QORs throughout evolution.

Crystal structures and putative interface of Saccharomyces cerevisiae mitochondrial matrix proteins Mmf1 and Mam33.

The yeast Saccharomyces cerevisiae mitochondrial matrix factor Mmf1, a member in the YER057c/Yigf/Uk114 family, participates in isoleucine biosynthesis and mitochondria maintenance. Mmf1 physically interacts with another mitochondrial matrix protein Mam33, which is involved in the sorting of cytochrome b2 to the intermembrane space as well as mitochondrial ribosomal protein synthesis. To elucidate the structural basis for their interaction, we determined the crystal structures of Mmf1 and Mam33 at 1.74 and 2.10 Å, respectively. Both Mmf1 and Mam33 adopt a trimeric structure: each subunit of Mmf1 displays a chorismate mutase fold with a six-stranded ß-sheet flanked by two α-helices on one side, whereas a subunit of Mam33 consists of a twisted six-stranded ß-sheet surrounded by five α-helices. Biochemical assays combined with structure-based computational simulation enable us to model a putative complex of Mmf1-Mam33, which consists of one Mam33 trimer and two tandem Mmf1 trimers in a head-to-tail manner. The two interfaces between the ring-like trimers are mainly composed of electrostatic interactions mediated by complementary negatively and positively charged patches. These results provided the structural insights into the putative function of Mmf1 during mitochondrial protein synthesis via Mam33, a protein binding to mitochondrial ribosomal proteins.

Structural characterization and functional analysis of juvenile hormone diol kinase from the silkworm, Bombyx mori.

Juvenile hormone diol kinase (JHDK) is an important enzyme involved in the juvenile hormone metabolism pathway, which catalyzes the phosphorylation of juvenile hormone diol to form the polar metabolite JH diol phosphate. Here, we reported the first crystal structure of insect JHDK from Bombyx mori, BmJHDK-L2, determined at a resolution of 1.22 Å. The structure of BmJHDK-L2 mainly comprises of eight α-helical segments linked with loops, forming four helix-loop-helix motifs. In these four helix-loop-helix motifs with only one calcium ion bound in the first motif. Circular dichroism spectra indicated that BmJHDK-L2 has strong thermal stability, which is independent of the divalent cation. The structure of BmJHDK-L2 further allowed us to define an ATP-binding site using computational simulation and binding assays, providing a structural basis for development of inhibitor of JHDK. Moreover, the expression profile of BmJHDK-L2 indicated a predominant role in juvenile hormone metabolism in the Malpighian tubules of silkworm. Collectively, these findings expand our knowledge regarding the structural and biochemical features of insect JHDK proteins.

Five Silkworm 30K Proteins Are Involved in the Cellular Immunity against Fungi.

BACKGROUND: 30K proteins are a major group of nutrient storage proteins in the silkworm hemolymph. Previous studies have shown that 30K proteins are involved in the anti-fungal immunity; however, the molecular mechanism involved in this immunity remains unclear. METHODS: We investigated the transcriptional expression of five 30K proteins, including BmLP1, BmLP2, BmLP3, BmLP4, and BmLP7. The five recombinant 30K proteins were expressed in an Escherichia coli expression system, and used for binding assays with fungal cells and hemocytes. RESULTS: The transcriptional expression showed that the five 30K proteins were significantly upregulated after injection of pathogen-associated molecular patterns to the fifth instar larvae, indicating the possibility of their involvement in immune response. The binding assay showed that only BmLP1 and BmLP4 can bind to both fungal cells and silkworm hemocytes. Furthermore, we found that BmLP1-coated and BmLP4-coated agarose beads promote encapsulation of hemocytes in vitro. The hemocyte encapsulation was blocked when the BmLP1-coated beads were preincubated with BmLP1 specific polyclonal antibodies. CONCLUSIONS: These results demonstrate that 30K proteins are involved in the cellular immunity of silkworms by acting as pattern recognition molecules to directly recruit hemocytes to the fungal surface.