AA15 lytic polysaccharide monooxygenase is required for efficient chitinous cuticle turnover during insect molting

Functional variation among LPMOs revealed by the inhibitory effects of cyanide and buffer ions

Enzymes known as lytic polysaccharide monooxygenases (LPMOs) are mono-copper polysaccharide-degrading peroxygenases that engage in several on- and off-pathway redox reactions involving O2 and H2O2. Herein, we show that the known metalloenzyme inhibitor cyanide inhibits reductive activation of LPMOs by binding to the LPMO-Cu(II) state and that the degree of inhibition depends on the concentrations of the polysaccharide substrate, the reductant and H2O2. Importantly, this analysis revealed differences between fungal NcAA9C and bacterial SmAA10A, which have different secondary copper coordination spheres. These differences were also highlighted by the observation that phosphate, a commonly used buffer ion, strongly inhibits NcAA9C while not affecting reactions with SmAA10A. The results provide insight into LPMO inhibition and catalysis and highlight pitfalls in the analysis thereof.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

Molecular evolution of dietary shifts in ladybird beetles (Coleoptera: Coccinellidae): from fungivory to carnivory and herbivory

BACKGROUND

Dietary shifts are major evolutionary steps that shape ecological niches and biodiversity. The beetle family Coccinellidae, commonly known as ladybirds, first transitioned from a fungivorous to an insectivorous and subsequently a plant diet. However, the molecular basis of this dietary diversification remained unexplored.

RESULTS

We investigated the molecular evolution of dietary shifts in ladybirds, focusing on the transitions from fungivory to carnivory (Coccinellidae) and from carnivory to herbivory (Epilachnini), by comparing 25 genomes and 62 transcriptomes of beetles. Our analysis shows that chemosensory gene families have undergone significant expansions at both nodes of diet change and were differentially expressed in feeding experiments, suggesting that they may be related to foraging. We found expansions of digestive and detoxifying gene families and losses of chitin-related digestive genes in the herbivorous ladybirds, and absence of most plant cell wall-degrading enzymes in the ladybirds dating from the transition to carnivory, likely indicating the effect of different digestion requirements on the gene repertoire. Immunity effector genes tend to emerge or have specific amino acid sequence compositions in carnivorous ladybirds and are downregulated under suboptimal dietary treatments, suggesting a potential function of these genes related to microbial symbionts in the sternorrhynchan prey.

CONCLUSIONS

Our study provides a comprehensive comparative genomic analysis to address evolution of chemosensory, digestive, detoxifying, and immune genes associated with dietary shifts in ladybirds. Ladybirds can be considered a ubiquitous example of dietary shifts in insects, and thus a promising model system for evolutionary and applied biology.

Plasma-Activated Water Boosts the Activity of Lytic Polysaccharide Monooxygenase and the Conversion of Chitin by a Chitinolytic Enzyme Cocktail

The plasma-activated water (PAW) containing numerous reactive species can facilitate chitin degradation. Given the intricate interplay between PAW treatment and the diverse activities of chitinolytic enzymes, further investigation is imperative for enhancing the chitin bioconversion efficiency. This study revealed that PAW-treated chitin exhibited improved degradability toward BtLPMO10A, endochitinases OfChtI, OfChtII-B4C1, and exochitinase OfChi-h. Furthermore, H2O2 in PAW boosted BtLPMO10A, whereas the soluble constituents in PAW generated during chitin pretreatment inhibited OfChi-h. Notably, this inhibition effect toward OfChi-h can be mitigated by the addition of β-N-acetylhexosaminidase. In the end, the synergy among the chitinolytic enzyme was also promoted by PAW pretreatment. On this as a basis, a chitin degradation strategy using a combination of PAW treatment and an enzyme cocktail was applied to degrade chitin, achieving a chitin conversion yield of 97% within 2 h. This strategy could also be applied to the degradation of other polysaccharides, such as cellulose.

Effects of prolonged NaHCO3 exposure on the serum immune function, antioxidant capacity, intestinal tight junctions, microbiota, mitochondria, and autophagy in crucian carp (Carassius auratus)

This study investigated the effects of long-term NaHCO3 stress on serum immunity, antioxidant capacity, intestinal tight junction, intestinal microbiota, mitochondrial function and autophagy in crucian carp. A total of 240 fish (31.19 ± 1.03 g) were randomly allocated to two groups and treated with 0 mmol/L (CK) and 50 mmol/L NaHCO3 (CA) respectively, to simulate the carbonate alkaline water environment. All of the experimental fish were cultured for 8 weeks. The results showed that compared to the control group, NaHCO3 stress significantly decreased the levels of the serum immunity indices (AKP, ACP, C3, C4, IgM, LZM) and the antioxidant capacity indices (CAT, GSH-PX, SOD, T-AOC), while markedly increasing the content of MDA. Additionally, NaHCO3 influenced the mRNA expression of HSP90, Nrf2, Keap1, and HO-1. Compared to the control group, the levels of ZO-1, Claudin-2, Occludin-a, and Occludin-b mRNA significantly decreased in the NaHCO3 stress group. The levels of ATG5, ATG7, and Beclin1 mRNA and protein were significantly increased along with the levels of LC3b mRNA and the ratio of protein LC3 II /LC3 I. Compared to the control group, intestinal mitochondria in the NaHCO3 stress group were visibly swollen and largely broken, with reductions in ridges and a large proportion of the area dissolved in the matrix. The mitochondrial membrane potential and the activities of ATPase were significantly decreased, leading to mitochondria dysfunction. In addition, 3147 differentially expressed genes were identified from transcriptome sequencing, among which several genes related to mitochondria and autophagy were significantly enriched. Compared to the control group, the NaHCO3 stress decreased the ACE index and increased the abundance of Proteobacteria while decreased the abundance of Actinobacteria and Firmicutes. In conclusion, NaHCO3 induced oxidative damage, microbiota alterations, mitochondria dysfunction, and autophagy in the intestines of crucian carp. The results of this study have characterized the molecular mechanisms of intestinal injury in crucian carp caused by NaHCO3 stress, and thus provide empirical support for aquaculture in saline-alkali waters.

Comparative genomics reveals carbohydrate enzymatic fluctuations and herbivorous adaptations in arthropods

Background

Arthropods represent the largest and most diverse phylum on Earth, playing a pivotal role in the biosphere. One key to their evolutionary success is their ability to feed on plant material. However, their endogenous enzymatic repertoire, which contributes to plant digestion, remains largely unexplored and poorly understood.

Results

We analyzed 815 arthropod proteomes and identified a total of 268,171 carbohydrate-active modules. Our findings revealed a strong correlation between enzymatic content and feeding habits, with herbivorous species possessing significantly higher enzyme levels. We identified widespread carbohydrate-active families across the AA, CBM, GH, and GT classes, and observed a progressive increase in taxa-exclusive families in more recent arthropod lineages. Notably, we highlighted the impact of the transition from ametabolous to holometabolous development on carbohydrate metabolism, as well as the ecological adaptations of different species groups. By reconstructing the ancestral enzymatic profiles of arthropods, we identified significant fluctuations in 10 carbohydrate-active families over time.

Conclusions

Our analysis advances the understanding of the evolutionary mechanisms utilized by the megadiverse phylum Arthropoda. We emphasize the critical role of herbivory as a selective force shaping enzymatic strategies, particularly those involved in carbohydrate metabolism. The distribution and exclusivity of carbohydrate-active families across different arthropod groups provide insights into their evolutionary trajectories and offer a clearer picture of the metabolic pathways that led their ancestors to their present forms.

Tissue-specific alternative splicing and the functional differentiation of LmLPMO15-1 in Locusta migratoria

Insect lytic polysaccharide monooxygenases (LPMO15s) are newly discovered copper-dependent enzymes that promote chitin degradation in insect through oxidative cleavage of glycosidic bonds. They are potential pesticide targets due to their critical role for chitin turnover in the integument, trachea, and peritrophic matrix of the midgut during insect molting. However, the knowledge about whether and how LPMO15s participate in chitin turnover in other tissues is still insufficient. Here, using the orthopteran pest Locusta migratoria as a model, a novel alternative splicing site of LmLPMO15-1 was discovered and it produces 2 variants, LmLPMO15-1a and LmLPMO15-1b. The transcripts of LmLPMO15-1a and LmLPMO15-1b were specifically expressed in the trachea and foregut, respectively. RNA interference targeting LmLPMO15-1 (a common fragment shared by both LmLPMO15-1a and LmLPMO15-1b), a specific region of LmLPMO15-1a or LmLPMO15-1b all significantly reduced survival rate of nymphs and induced lethal phenotypes with developmental stasis or molt failure. Ultrastructure analysis demonstrated that LmLPMO15-1b was specifically involved in foregut old cuticle degradation, while LmLPMO15-1a was exclusively responsible for the degradation of the tracheal old cuticle. This study revealed LmLPMO15-1 achieved tissue-specific functional differentiation through alternative splicing, and proved the significance of the spliced variants during insect growth and development. It provides new strategies for pest control targeting LPMO15-1.

The beetle's structural protein CPCFC making elytra tough and rigid

The insect cuticle, which serves as both a protective barrier and an efficient lever system for locomotion, is an extracellular matrix primarily composed of chitin and protein. The cuticle protein CPCFC characterized by a "CFC" motif containing 2 Cys split by the insertion of 5 residues is distributed across most insect species and specifically localized in the hard part of the cuticle. However, their physiological function is not fully understood. Here, we report 2 CPCFC proteins, TcCPCFC1 and TcCPCFC2, derived from the Coleopteran insect Tribolium castaneum. We revealed that TcCPCFC1 and TcCPCFC2 were predominantly expressed during the larval and adult stages of T. castaneum, respectively. The transcription downregulation of TcCPCFC1 significantly decreased the modulus and toughness of the elytral cuticle. We found that TcCPCFC proteins have high binding affinity to chitin. We cloned and produced recombinant TcCPCFC proteins and demonstrated that the addition of TcCPCFC proteins to chitin hydrogel greatly enhanced the hydrogel's modulus and toughness by forming denser chitin fibrous networks. Our findings reveal the functional role of CPCFC proteins in enhancing mechanical properties of insect cuticle, and we validate this process in vitro, and offer a protein candidate for fabrication of advanced chitin-based materials.

Functional role of carbohydrate-binding modules in multi-modular chitinase OfChtII

The primary distinction between insect and bacterial chitin degradation systems lies in the presence of a multi-modular endo-acting chitinase ChtII, in contrast to a processive exo-acting chitinase. Although the essential role of ChtII during insect development and its synergistic action with processive chitinase during chitin degradation has been established, the mechanistic understanding of how it deconstructs chitin remains largely elusive. Here OfChtII from the insect Ostrinia furnacalis was investigated employing comprehensive approaches encompassing biochemical and microscopic analyses. The results demonstrated that OfChtII truncations with more carbohydrate-binding modules (CBMs) exhibited enhanced hydrolysis activity, effectively yielding a greater proportion of fibrillary fractions from the compacted chitin substrate. At the single-molecule level, the CBMs in these OfChtII truncations have been shown to primarily facilitate chitin substrate association rather than dissociation. Furthermore, a greater number of CBMs was demonstrated to be essential for the enzyme to effectively bind to chitin substrates with high crystallinity. Through real-time imaging by high-speed atomic force microscopy, the OfChtII-B4C1 truncation with three CBMs was observed to shear chitin fibers, thereby generating fibrillary fragments and deconstructing the compacted chitin structure. This work pioneers in revealing the nanoscale mechanism of endo-acting multi-modular chitinase involved in chitin degradation, which provides an important reference for the rational design of chitinases or other glycoside hydrolases.

Crucial roles of specialized chitinases in elytral and hindwing cuticles construction in Leptinotarsa decemlineata

BACKGROUND

The Colorado potato beetle (CPB), Leptinotarsa decemlineata, is a major potato (Solanum tuberosum) pest, infesting over 16 million km2 and causing substantial economic losses. The insect cuticle forms an apical extracellular matrix (ECM) envelope covering exposed organs to direct morphogenesis and confer structural protection. While select chitinase (Cht) genes have proven essential for larval development, their potential activities directing ECM remodeling underlying adult wing maturation remain undefined.

RESULTS

We investigated the expression patterns and performed an oral RNA interference (RNAi) screen targeting 19 LdChts in late-instar L. decemlineata larvae. Subsequently, we assessed their effects on adult eclosion and wing characteristics. Knockdown of LdCht5, LdCht7, LdCht10, LdIDGF2, and LdIDGF4, as well as others from Group IV (LdCht15, LdCht12, LdCht17, and LdCht13) and Groups VII-X (LdCht2, LdCht11, LdCht1, and LdCht3), resulting in shrunken, misshapen elytra with reduced areal density, as well as transverse wrinkling and impaired wing-tip folding in hindwings. Scanning electron micrographs revealed eroded elytral ridges alongside thinned, ruptured hindwing veins, indicative of mechanical fragility post-LdCht suppression. Spectroscopic analysis uncovered biomolecular alterations underlying the elytral anomalies, including decreases in peaks representing chitin, proteins, and lipids. This loss of essential ECM components provides evidence for the fragility, wrinkling, and shrinkage observed in the RNAi groups.

CONCLUSION

Our findings elucidate the crucial role of chitinases in the turnover of chitinous cuticles on beetle wings, offering insights into RNAi-based control strategies against this invasive pest. © 2024 Society of Chemical Industry.

Identification and Functional Insights of Knickkopf Genes in the Larval Cuticle of Leptinotarsa decemlineata

The Colorado potato beetle (Leptinotarsa decemlineata) is a major pest of potato crops. While Knickkopf (Knk) genes are essential for insect cuticle formation, their roles in pests like L. decemlineata remain unclear. This study aims to identify and characterize Knk genes in L. decemlineata and explore their functions in larval development and cuticle integrity. We used genomic and transcriptomic databases to identify LdKnk-family genes, validated through RT-PCR and RACE. Gene expression was analyzed at various developmental stages and tissues using qRT-PCR. RNA interference (RNAi) and Transmission electron microscopy (TEM) were applied to determine the functional roles of these genes. Four LdKnk-family genes were identified. Spatio-temporal expression analysis indicated significant gene expression during larval molting and pupal stages, especially in the epidermis. RNAi experiments showed that silencing LdKnk and LdKnk3-5' led to reduced larval weight, cuticle thinning, and increased mortality, while LdKnk3-FL knockdown caused abnormal cuticle thickening and molting disruptions. LdKnk2 knockdown increased epicuticle and endocuticle thickness without visible phenotypic changes. The study highlights the essential roles of LdKnk-family genes in maintaining cuticle structure and integrity, suggesting their potential as targets for RNAi-based pest control.

Microorganism Contribution to Mass-Reared Edible Insects: Opportunities and Challenges

The interest in edible insects' mass rearing has grown considerably in recent years, thereby highlighting the challenges of domesticating new animal species. Insects are being considered for use in the management of organic by-products from the agro-industry, synthetic by-products from the plastics industry including particular detoxification processes. The processes depend on the insect's digestive system which is based on two components: an enzymatic intrinsic cargo to the insect species and another extrinsic cargo provided by the microbial community colonizing-associated with the insect host. Advances have been made in the identification of the origin of the digestive functions observed in the midgut. It is now evident that the community of microorganisms can adapt, improve, and extend the insect's ability to digest and detoxify its food. Nevertheless, edible insect species such as Hermetia illucens and Tenebrio molitor are surprisingly autonomous, and no obligatory symbiosis with a microorganism has yet been uncovered for digestion. Conversely, the intestinal microbiota of a given species can take on different forms, which are largely influenced by the host's environment and diet. This flexibility offers the potential for the development of novel associations between insects and microorganisms, which could result in the creation of synergies that would optimize or expand value chains for agro-industrial by-products, as well as for contaminants.

Multicopper oxidase-2 mediated cuticle formation: Its contribution to evolution and success of insects as terrestrial organisms

The insect cuticle is a non-cellular matrix composed of polysaccharide chitins and proteins. The cuticle covers most of the body surface, including the trachea, foregut, and hindgut, and it is the body structure that separates the intraluminal environment from the external environment. The cuticle is essential to sustain their lives, both as a physical barrier to maintain homeostasis and as an exoskeleton that mechanically supports body shape and movement. Previously, we proposed a theory about the possibility that the cuticle-forming system contributes to the "evolution and success of insects." The main points of our theory are that 1) insects evolved an insect-specific system of cuticle formation and 2) the presence of this system may have provided insects with a competitive advantage in the early land ecosystems. The key to this theory is that insects utilize molecular oxygen abundant in the atmosphere, which differs from closely related crustaceans that form their cuticles with calcium ions. With newly obtained knowledge, this review revisits the significance of the insect-specific system for insects to adapt to terrestrial environments and also discusses the long-standing question in entomology as to why, despite their great success in terrestrial environments, they poorly adapt to marine environments.

The disordered C-terminal tail of fungal LPMOs from phytopathogens mediates protein dimerization and impacts plant penetration

Lytic polysaccharide monooxygenases (LPMOs) are monocopper enzymes that oxidatively degrade various polysaccharides, such as cellulose. Despite extensive research on this class of enzymes, the role played by their C-terminal regions predicted to be intrinsically disordered (dCTR) has been overlooked. Here, we investigated the function of the dCTR of an LPMO, called CoAA9A, up-regulated during plant infection by Colletotrichum orbiculare, the causative agent of anthracnose. After recombinant production of the full-length protein, we found that the dCTR mediates CoAA9A dimerization in vitro, via a disulfide bridge, a hitherto-never-reported property that positively affects both binding and activity on cellulose. Using SAXS experiments, we show that the homodimer is in an extended conformation. In vivo, we demonstrate that gene deletion impairs formation of the infection-specialized cell called appressorium and delays penetration of the plant. Using immunochemistry, we show that the protein is a dimer not only in vitro but also in vivo when secreted by the appressorium. As these peculiar LPMOs are also found in other plant pathogens, our findings open up broad avenues for crop protection.

Identification of chitinase genes and roles in the larval-pupal transition of Leptinotarsa decemlineata

BACKGROUND

Insect chitinases play crucial roles in degrading chitin in the extracellular matrix, affecting insect development and molting. However, our understanding of the specific functions of various chitinases in Leptinotarsa decemlineata is limited, hindering the deployment of novel gene-targeting technologies as pest management strategies.

RESULTS

We identified and characterized 19 full-length complementary DNA (cDNA) sequences of chitinase genes (LdChts) in Leptinotarsa decemlineata. Despite having varying domain architectures, all these chitinases contained at least one chitinase catalytic domain. Phylogenetic analysis classified the chitinase proteins into ten distinct clusters (groups I-X). Expression profiles showed the highest expression in chitin-rich tissues or during specific developmental stages from the larva-to-pupa transition. Gene-specific RNA interference (RNAi) experiments provided valuable insight into chitinase gene function. Silencing of group II LdCht10 prevented larval-larval molting, larval-prepupal, and prepupal-pupal processes. Moreover, our study revealed that LdCht5, LdCht2, LdCht11, LdCht1, and LdCht3 from groups I and VII-X were specifically essential for the transition from prepupal to pupal stage, whereas LdIDGF2 from group V was necessary for the larval-prepupal metamorphic process. The chitinase gene LdCht7 from group III and LdIDGF4 from group V were involved in both the larva-to-prepupa and the prepupa-to-pupa shift. Additionally, our findings also shed light on the exclusive expression of nine chitinase genes within group IV in the digestive system, suggesting their potential role in regulating larval body weight and larva-to-pupa transition.

CONCLUSION

Our results provide a comprehensive understanding of the functional specialization of chitinase genes during the molting process of various stages and identify potential targets for RNAi-based management of Leptinotarsa decemlineata. © 2023 Society of Chemical Industry.

Functional importance of groups I and II chitinases in cuticle chitin turnover during molting in a wood-boring beetle, Monochamus alternatus

Insects must periodically replace their old cuticle/exoskeleton with a new one in a process called molting or ecdysis to allow for continuous growth through sequential developmental stages. Many RNA interference (RNAi) studies have demonstrated that certain chitinases (CHTs) play roles in this vital physiological event because knockdown of these CHT genes resulted in developmental arrest during the ensuing molting period in several insect species. In this research we analyzed the functions of group I (MaCHT5) and group II (MaCHT10) CHT genes in molting of the Japanese pine sawyer, Monochamus alternatus, an important forest pest known as a major vector of the pinewood nematode. Real-time qPCR revealed that these two CHT genes differ in their expression patterns during late stages of development. Depletion of either MaCHT5 or MaCHT10 transcripts by RNAi resulted in lethal larval-pupal and pupal-adult molting defects depending on the double-stranded RNA (dsRNA) injection timing during development. The insects were unable to shed their old cuticle and died. Furthermore, transmission electron microscopic analysis revealed that, unlike dsEGFP-treated controls, dsMaCHT5- and dsMaCHT10-treated pharate adults exhibited a failure of degradation of the endocuticular layer of their old pupal cuticle, retaining nearly intact horizontal chitinous laminae and vertical pore canal fibers. Both enzymes were indispensable for complete turnover of the chitinous old endocuticle, which is critical for insect molting. The possible functions of two spliced variants of MaCHT10, namely, MaCHT10a and MaCHT10b, are also discussed. Our results add to the knowledge base for further functional studies of insect chitin catabolism by revealing the relative importance of both MaCHT5 and MaCHT10 in chitin turnover with subtle differences in their action. These essential genes and their encoded proteins are potential targets to manipulate for controlling populations of M. alternatus and other pest insects.

Biocatalytic potential of Pseudolycoriella CAZymes (Sciaroidea, Diptera) in degrading plant and fungal cell wall polysaccharides

Soil biota has a crucial impact on soil ecology, global climate changes, and effective crop management and studying the diverse ecological roles of dipteran larvae deepens the understanding of soil food webs. A multi-omics study of Pseudolycoriella hygida comb. nov. (Diptera: Sciaroidea: Sciaridae) aimed to characterize carbohydrate-active enzymes (CAZymes) for litter degradation in this species. Manual curation of 17,881 predicted proteins in the Psl. hygida genome identified 137 secreted CAZymes, of which 33 are present in the saliva proteome, and broadly confirmed by saliva CAZyme catalytic profiling against plant cell wall polysaccharides and pNP-glycosyl substrates. Comparisons with two other sciarid species and the outgroup Lucilia cuprina (Diptera: Calliphoridae) identified 42 CAZyme families defining a sciarid CAZyme profile. The litter-degrading potential of sciarids corroborates their significant role as decomposers, yields insights to the evolution of insect feeding habits, and highlights the importance of insects as a source of biotechnologically relevant enzymes.

Lytic polysaccharide monooxygenase - A new driving force for lignocellulosic biomass degradation

Lytic polysaccharide monooxygenases (LPMOs) can catalyze polysaccharides by oxidative cleavage of glycosidic bonds and have catalytic activity for cellulose, hemicellulose, chitin, starch and pectin, thus playing an important role in the biomass conversion of lignocellulose. The catalytic substrates of LPMOs are different and the specific catalytic mechanism has not been fully elucidated. Although there have been many studies related to LPMOs, few have actually been put into industrial biomass conversion, which poses a challenge for their expression, regulation and application. In this review, the origin, substrate specificity, structural features, and the relationship between structure and function of LPMOs are described. Additionally, the catalytic mechanism and electron donor of LPMOs and their heterologous expression and regulation are discussed. Finally, the synergistic degradation of biomass by LPMOs with other polysaccharide hydrolases is reviewed, and their current problems and future research directions are pointed out.